Herbaceous Perennial Plants: A Treatise on their Identification, Culture, and Garden Attributes

By Allan M. Armitage

The third edition of the comprehensive—and entertaining—gardening reference by the master horticulturalist.

This is the long-awaited third edition of Allan Armitage’s masterpiece on garden perennials. Armitage’s extensive traveling, teaching, and trialing experiences provide a depth of understanding of the best ornamental perennials for North American gardens unparalleled by any other garden writer.

One of the most definitive and conclusive books written about perennials, the first edition was designated as one of the best seventy-five books written in the last seventy-five years by the American Horticulture Society. Now the third edition of “The Big Perennial Book” (as it is fondly referred to by many practitioners) describes 3,600 species in 1224 pages. More than three hundred color photos complement detailed text filled with the author’s pointed observations of plant performance, cultivar selection, and current taxonomy. In addition, his trademark wit and passion are both in abundance, making reading as pleasurable as it is informative.

• Language: English
• Publisher: Open Road Integrated Media
• Release date: May 1, 2008
• ISBN: 9781610583800

Book preview

Some Thoughts of the Author

On a Third Edition:

While awash in obscure cultivars of an obscure genus at 5:00 on an obscure morning, I asked myself why I was doing this. In fact, that question arose on many obscure mornings. The reasons are many, but the only one that counts is Because I want to. I love this book; I love seeing it in peoples’ hands, on bookshelves, in retail garden centers, on coffee tables, and worn out and tattered in the garden. As I’ve wandered around gardens and nurseries since the second edition was published, it was obvious that new cultivars, new genera and new names had to be brought up to date. Books on perennials come and go, but damned if I was going to watch this one end up on the clearance table in some Book Mart. Writing a new edition is not nearly as sexy as writing a new book, but almost as difficult. So, here it is, not because I had to, but because I wanted to.

On the Internet vs. Books:

When the first edition was written in 1989, the Internet was in its infancy, crashing around like a drunken sophomore. As I finished the second edition in 1997, far more information was available, and the future of this medium was pretty obvious. In 2008, there is no subject that cannot be searched, found, and occasionally believed on the Internet. Information about plants is everywhere, from catalogs and photos, to personal opinions about every plant (and author) known to man. How many times have I been told that people (especially young people) don’t read any more, so why bother with all those printed words when you can find an e-book online? I have been asked Why write a reference book that will be out of date when the next catalog appears, especially when anyone can find information for free at home? Perhaps I am an old fogey, but for me, books will never go away, and a good book becomes a friend. I have never felt the same contentment hunched over a laptop wired to God knows where, as I have when curled in a comfy chair with a good book. Never will. Perhaps books will go the way of the VCR, and perhaps Gens X, Y and Z may never read a word I write, but I’ll still keep penning away. See you in that comfy chair.

Having said that, the Internet has made buying plants, especially unusual plants, easier than ever before. Specialty nurseries can attract customers from all over the country more efficiently and with less expense than sending out thousands of paper catalogs. If the Internet has changed anything, it is not what we read but how we buy. Today, the successful nurseryman and the inquisitive gardener more frequently meet online in the ether, not in line at the store.

On the Decline of Gardening:

If I listened to the plant marketing gurus out there, I would believe that gardening is on its deathbed. According to them, nobody cares about plants, only plant function. Nobody cares about gardens, only lifestyles. Heck, so few people actually garden anymore that it is amazing any plants are sold at all. I have heard so many times that gardening is work, nobody wants to work, too much time, too much effort, yada, yada, yada, that I am nauseated. I might even believe such drivel if I was a marketing fellow, but those comments aren’t at all consistent with my experiences. Perhaps they need to join me for a few weeks when I speak to gardeners and industry people like you. The hundreds and hundreds of gardeners who find their way to my talks are not coming to see my pretty face. They are there because they love the subject, and can’t get enough. Good grief, look at the catalogs, look at the stores—people would not be spending money on breeding, promotion and distribution of plants if they believed nobody cared. I have no doubt the markets are changing, and no doubt that the data are real, but gardening and gardeners aren’t going anywhere for a long time.

That is not to say change has not occurred. One of the disturbing trends has been the closing of some fine nurseries since the last edition was published. Most times, such shut-downs are normal; competition, poor management, or tired owners who want to relax a little more. Online sites and newer ventures have more than made up for the number of nurseries that have been lost; however, when places like Heronswood Nursery in Oregon shutters its northwestern doors, we are all a little wounded.

On the Meaning of Gardening:

When gardeners are asked to describe reasons for gardening, three words emerge time and again: therapeutic, creative and exciting. Such words are more often associated with sporting events than gardening, however, therapy, creativity, and excitement are integral parts of gardening.

Therapeutic, because of the feeling that all is well with the world when our hands are in Mother Earth. Therapeutic because when a seed is sown, a cutting rooted, or seedling planted, we have accomplished something important.

Creative, because artistry is an inescapable part of gardening. A swath of Astilbe brightens the shade, a grouping of cool-leaved Artemisia brings calm to its neighbors, and a half dozen forget-me-nots sing of spring. Each grouping creates vistas of beauty. We do not require a degree in landscape architecture to create such beauty; all we need is the simple love of gardening.

Exciting is a word seldom attributed to gardening. But is it not exciting to watch a garden change with time? To watch Asarum, wild ginger, bull through the soil in early spring, anticipate the popping of the buds of balloon flower, and anticipate the magic of the re-emergence of resurrection flower, is truly exciting.

Voices about Gardening:

Perhaps a couple of quotes from the past are also appropriate. The first is attributed to the great plant hunter Ernest Henry Wilson, who wrote it just three years before his death in 1930. There are no happier folk than plant-lovers and none more generous than those who garden. There is a delightful freemasonry about them; they mingle on a common plane, share freely their knowledge and with advice help one over the stepping stones that lead to success. It is truthfully said that a congenial companion doubles the pleasures and halves the discomforts of travel and so it is with the brotherhood who love plants. E. H. Wilson, Plant Hunting, v.1, 1927.

A second quote comes from another one of my former students, who wrote an essay on the why people embrace perennials in their gardens. Those who believe our students aren’t among the finest in the world need to come and visit my classes.

Americans, as a rule, live with a certain sense of urgency. Perhaps this is the price we pay for living in such a young country. Why waste time with some fickle plant which will flower only for a few short moments each year when there are countless annuals just begging to bloom all summer long? The commitment perennials require represents the driving force behind gardening as a whole. When someone kills a window box of petunias, there is no love lost. Odds are that a quick trip to Kmart will have the window box blooming again in short order. Let there be no doubt about the glorious beauty of a well-planted annual garden. But, for all their show and eager-ness-to-please, annuals provoke no anticipation. To be among an established garden teaches one why we have gardens at all; gardens are our refuge from the irritations of everyday life, a place of peace, serenity and provide the hope and anticipation of good things to come. Ken James, student, 1995. By the way, today, Ken and his wife Leah are proud owners of James Greenhouses in beautiful Colbert, Georgia, and are exceptional growers of perennials.

On a Garden:

A garden is a melding of different plants, including trees, shrubs, and herbaceous species. A garden lacks grandeur and grace without the architecture and framework provided by stately trees. A single specimen, such as a cedar of Lebanon, can define an entire garden. Like a snow-capped mountain in the distance, it is never out of sight or out of mind. Shrubs are indispensable for screening, massing, form and texture. From abelia to Zenobia, they provide the glue that bonds the trees and herbaceous plants together. Broad sweeps of annuals such as geraniums, celosia and marigolds provide interest through the gardening season and, like magnets, draw the eye to their carpet of color. Herbaceous perennials add a unique charm and flavor to any garden.

There are few times when perennials do not add interest and change. From barren winter ground, through frenzied activity in the spring, until flower buds are visible, perennials are always changing. Finally, the flowers can wait no longer and islands of color blaze like flares in the night. Many have foliage more colorful than flowers, fruits that compete with holly, and fall colors as dramatic as sugar maples. To the connoisseur and amateur, there is nothing more colorful and interesting than a well-conceived perennial border. However, all great borders have backdrops of hedges or tree canopies, and annuals to fill in gaps. Perennials are an important part of the garden but are just that, a part of the garden. Perennials or a perennial border should be woven into a garden, rather than being the garden. Such a garden is much more beautiful than the sum of the beauty of the individual parts.

On a Gardener:

Gardening is hard work! Low maintenance does not mean no maintenance. No maintenance gardening does not exist, although lower maintenance is possible with proper plant selection. I travel and talk with gardeners of all ages all the time. I have met sore gardeners, tired gardeners and broke gardeners, but I’ve never met an old gardener. If anything defines a gardener, it is his belief in the future. It is impossible to get old when one is always thinking about the future. Planting bulbs in the fall turns one’s thoughts to spring, planting a small tree today transports us to its cool shade tomorrow. Gardening simply does not allow one to be mentally old, because there are too many plants and beauty yet to be realized.

The one absolute of gardeners is faith. Regardless of how bad past gardens have been, every gardener believes that next year’s will be better. We even still believe that the descriptions and photos in catalogs are true! Yes, we are a trusting bunch. It is easy to age when there is nothing to believe in, nothing to hope for; gardeners, however, simply refuse to grow up. As Thomas Jefferson so eloquently stated Though an old man, I am but a young gardener.

On North and South:

Many of the same species are cultivated in Montreal, Canada, and Athens, Georgia, areas characterized, as far north and deep south. I have gardened in both places as well as in East Lansing, Michigan and traveled with open eyes throughout the United States, Canada, Australia, New Zealand, the Mideast, South Africa and much of Europe. Certain species may thrive in one area but perform poorly in another. Obvious climatic differences exist among areas in North America, and even subtle differences within a garden influence plant performance. No absolute demarcation exists where North ends and South begins, but in this book the South incorporates zones 7-10 of the United States Department of Agriculture Hardiness Zone Map. Zone 7 (minimum 0-10°F) ranges as far north as Rhode Island, into Virginia, and cuts across Tennessee, Arkansas, central Oklahoma, central Texas, southern New Mexico and into Arizona and California. Many climatic factors interact with the plants’ ability to thrive or languish in a given zone, and hardiness ratings must be treated cautiously (see On Hardiness Ratings).

Several differences are obvious between plants of the same species grown in northern and southern locales. In the South, temperate zone plants flower earlier, are taller and may have weaker stems due to the accumulated heat. Tall forms tend to collapse without support and dwarf selections are usually more effective in the southern garden. Fertilizer need not be applied as generously in the South as in the North, particularly on tall cultivars, as additional growth is not the goal. Lanky, leggy growth occurs at the expense of flower production if too much nitrogen is applied. This happens regardless of latitude, but is more prominent in the South. The lack of snow is a major detriment to overwintering perennials anywhere. Snow provides insulation from the cold and plants tucked beneath the protective eiderdown survive cold winters well. That is why my friends in the Gaspe’ of Quebec (zone 3) claim that gardening is so easy there.

Where rain replaces snow (as in the South), the major survival problem is inadequate drainage. This is particularly true on heavy clay where cold winter rains result in soggy, water-logged soils and roots, crowns, and bulbs are immersed in free-standing water. Rot organisms proliferate and plants disappear, not because of lack of cold hardiness but because they rotted in the ground. Addition of bark, peat moss or other materials that aid drainage alleviate root rot problems. Summer temperatures and humidity in the South are also detriments to perenniality. Plants not adapted to the South often perform poorly because of high night temperatures. Plants use oxygen and release carbon dioxide (similar to humans) in the process of respiration. Heat significantly affects the rate of plant respiration. In general, for every 16°F rise in temperature, respiration doubles. When night temperatures remain above 70°F the process of respiration continues unabated and competes more aggressively for the carbohydrates produced during the day by photosynthesis. This results in lack of stored carbohydrates, inhibition of chlorophyll synthesis, and lack of secondary cell wall formation. The consequence is reduced vigor, weak stunted plants and small foliage. Species not capable of acclimatization cannot store the reserves necessary to survive the winter. In many cases, death is due not to lack of winter hardiness, but lack of summer tolerance. Many problems may be minimized with fall planting, allowing plants time to build starch reserves and develop an extensive root system prior to the onset of winter. Fall planting is more critical in the South than the North for most temperate species.

Reading all the problems associated with gardening in the South, one would believe that I think southern gardening is more difficult than northern gardening. I do. More difficult, but equally wonderful. I have gardened in Athens for over 25 years now, and I think I am finally getting the hang of it. I have a ball every day.

Regardless of where one gardens, two things become self-evident. The first is that soil preparation is half the battle. The second has to do with the plants one selects. Choosing plants that are adapted to the site and climate makes more sense than constantly trying to grow plants that are doomed to failure within a year or two. This is not to say that we shouldn’t experiment with plant selection—half the fun of gardening is to try plants that are not supposed to grow here. A quick read of good catalogs quickly shows that there is no end to species and cultivars to try, without trying to overwinter a plant native to the tropics.

On Hardiness Ratings:

United States Department of Agriculture (USDA) hardiness zones have been used by commercial growers and gardeners for many years. Zones provide guidelines to measure plants’ ability to survive cold temperatures. To be sure, they are imperfect but they are the best we have at present to objectively evaluate geographical limits of adaptability. The USDA hardiness map, published in 1990 (see page xxviii), is based on minimum winter temperatures and must be interpreted cautiously. In fact, with the obvious climate changes occurring today, minimum temperatures will rise and zone designations throughout North America are bound to inch up. Many factors affect plant growth other than average minimum temperatures. For example, zone 7 in Athens, Georgia is a different world from zone 7 in central California. Although minimum temperatures may be similar, summer temperatures during the night, humidity and rainfall are quite different. Valleys and mountains in the same hardiness zone are different climatically and plants that survive in higher elevations may perish when they descend 500 feet. Experienced gardeners will tell you they have multiple zones in their own gardens. Microclimates exist even in a small garden and plants that perform poorly in one location often perk up when moved to a more sheltered environment.

Heat tolerance is more difficult to evaluate than cold tolerance. Plants respond to cold by dying; to heat by languishing. However, heat tolerance or summer hardiness ratings are equally important in predicting plant performance. European garden literature is a rich source of information but descriptions must be taken with a grain of salt. Similarly, descriptions of plant habit in the North and West may not mirror performance in the South or East. This is primarily due to differences in summer hardiness. In this text, I have attempted to provide summer hardiness ratings for all species based on experimentation, observation, existing literature, and discussions with gardeners. The southern hardiness range listed is one in which the species performs well, if other factors such as shade, sun, or proper drainage are provided. Plants may survive south of that rating, but performance is significantly reduced. The ratings must not be considered gospel, but it is hoped they will add to the body of horticultural knowledge. Plants do not read, and testing species where they are not supposed to grow often provides pleasant surprises.

On Garden Design:

Design is an important aspect of gardening. Great garden designers are born, not made, and nurtured through observation and experience. Principles of design abound and even I try to adhere to the basics. Most importantly, the design should be pleasing to the owner and not planned with others in mind. Select one or two dominant colors that appeal and use colors that complement, rather than distract from each other. The aim of color is to tie plants together and then wed the planting to the site. One of the reasons for the popularity of gray and silver foliage, as well as white flowers, is their ability to unite the garden.

However, I am the first to admit that I am a poor designer. To me, the most important part of design is that the plants perform well in the site. I can usually be found with a trowel in one hand and a potted plant in the other, searching for any empty ground in which to place the sucker. Good performance is defined by persistent, fresh foliage, vigorous growth, and copious flower production. Selection on the basis of plant performance is more important than selection based on the color wheel. To totally ignore design, however, is to relegate a garden to a collection of plants.

Water features should be included in every garden. The presence of water, be it a birdbath, fountain, pond, or stream, does more to soften and define a garden than all other features combined. I am always learning about garden design and someday will discourse competently on hues, shapes, feelings, and combinations. Until then, however, I will enjoy the eclectic combination of plant material around my garden pond.

On Plant Nomenclature:

Plant names are no different than any other names; some are long and complicated, others are short and sweet. A scientific name defines a single species only, but a common name may describe a dozen or more. A valid scientific name is accepted throughout the world, regardless of language or politics. The science of nomenclature is practiced by taxonomists who attempt to bring order out of chaos. Because one of their goals is to validate current scientific names and replace incorrect ones, scientific names are constantly evolving. Two main problems occur when taxonomist meets gardener. The first occurs when a new scientific name replaces one of long standing. Chrysanthemum leucanthemum became Leucanthemum vulgare; Vinca rosea is Catharanthus roseus; Helleborus corsicus has become H. argutifolius; and the entire Aster and Cimicifuga genera have essentially disappeared. At times, it seems like a change in nomenclature is accomplished just to keep someone busy, however, if the new name is agreed on by taxonomic authorities, it should also be accepted by horticulturists and gardeners.

This brings up the second problem. Taxonomists don’t always agree. Names accepted by one authority aren’t necessarily accepted by other equally respected authorities due to valid differences of opinion and methodology. That leaves everyone in a muddle, so muddle we do.

Plants are listed by genus, species, variety and cultivar. A genus is a closely related group of plants consisting of one or more species. Species within a genus have more characteristics in common with each other than they do with species in other genera. Often genera are closely related and differences are difficult to discern. Silene and Delphinium are obviously different but telling the difference between Silene, Agrostemma and Lychnis is difficult. The genus name begins with an upper case letter and is underlined or written in italics. A species is difficult to define but may be thought of as a type of plant distinct from other types by identifiable features. The unique characteristics are reproducible from one generation to generation through seed. A species name begins with a lower case letter and is underlined or written in italics.

Often, individual plants may be slightly different from other members of the species and the definable characteristic is reproduced each generation. This group of plants is known as a variety and has enough similarities with others to be in the same species but is sufficiently different to be grouped as a separate variety. Often varieties are geographically distinct and have their own range. Varieties breed relatively true from seed, passing on their definable differences from parent to offspring. Varieties are preceded with var. and underlined or written in italics. For example, Muscari comosum var. monstrosum infers that a group of plants of Muscari comosum differs in some way to be placed in var. monstrosum, and reproduces this difference by seed.

A cultivar refers to a cultivated variety and may be the result of hybridization, random mutation, or plant selection. For our purposes, cultivar differs from variety in that the definable factors that make a cultivar unique are not passed on from generation to generation by seed. Cultivars are propagated vegetatively by tissue culture, cuttings, grafting or divisions (although commercial breeders maintain homozygous lines so seed-propagated cultivars may be offered). Cultivars begin with upper case letters and are enclosed by single quotation marks. For example, Lychnis coronaria ‘Abbotswood Rose’ has lighter pink flowers than the species. Seeds produced by plants of ‘Abbotswood Rose’ do not result in similar plants.

The distinction between variety and cultivar diminishes when varieties are given cultivar names. For example, var. alba is a common variety of many species and usually refers to the presence of white flowers. If those plants are marketed under a cultivar name such as ‘White Knight’ or ‘Snow White’, it is impossible to know if plants are reproducible sexually or asexually. Unfortunately, in horticultural and gardening circles, the terms cultivar and variety are used interchangeably.

Hybrids are common and characteristics from each parent may be found in the offspring. Interspecific hybrids are designated by an x and are usually reproducible only vegetatively. For example, Polygonatum x hybridum is a hybrid between P. multiflorum and P. odoratum and is reproduced by division of the rootstock. Intergeneric hybrids occasionally occur and are designated by an uppercase (X) before the name. X Heucherella alba is a hybrid between Heuchera brizoides and Tiarella wherryi. The X is not sounded.

I have attempted to sort out the nomenclature where possible. There is still a long way to go. Comments from readers are welcome.

On Common Names:

I like common names. Names like cardinal flower, resurrection lily, pussytoes, and blackberry lily are far more interesting than Lobelia cardinalis, Lycoris squamigera, Antennaria dioica, and Belamcanda chinensis. They also bring with them part of the history of discovery and use of the species. Lily-of-the-valley tells me more about the plant I am about to buy than Convallaria majalis, while lungwort describes a philosophy of naming plants much better than does Pulmonaria officinalis. Common names may describe the flower, such as pincushion flower (Scabiosa); leaves, spotted geranium, (Geranium maculatum); origin, Persian buttercup (Ranunculus asiaticus); medicinal properties, self-heal (Prunella vulgaris); or the discoverer, Stokes aster, (Stokesia). Unfortunately, the same common name may be used for more than one species or a single species may be known by several common names, depending on area of the country.

I have heard arguments from purists that common names are irrelevant and their use should not be encouraged. What nonsense! If one wants to see the demise of gardening, keep making it complicated. Gardening is way too complicated as it is, what with 30 cultivars of this, 10 of that and names that are unpronounceable even by Professor Higgins. Gardeners and professionals should encourage common names; they make what we do so much more user-friendly.

On Pronunciation:

Most people like to pronounce names with some degree of confidence. Scientific names can be intimidating and often we will not say them for fear of sounding ignorant. Like anything else, pronunciation is something that one feels confident with only with continued use. If scientific names are seldom part of one’s gardening vocabulary, we will always stumble and stutter. I have provided pronunciation guides for most genera and specific epithets principally based on books and articles but with a definite Armitage bias as well.

However, let’s get real. Does it really matter if paniculata is pronounced (pa-nik-ew-lah' ta) or (pa-nik-ew-lay' ta)? I prefer to pronounce Stokesia as (stokes' ee-a), in recognition of Dr. John Stokes, for whom the genus was named. However (stow-keys' ee-a) is commonly used and equally understood. So, here is the important part. Get the syllables in the right order, then fire away. Don’t worry about sounding silly, it is only the garden snob who continually tries to correct you. And who needs snobs in a garden?

On The Most Important Thing:

The most important thing about gardening is to have fun. There will be aches, frustration, money poorly spent and disappointment, but the pleasure should always outweigh the pain. Don’t get serious, ever, about gardening. The worst oxymoron in all of horticulture is serious gardener. Don’t be one; let it wash over you and enjoy the day.

An Explanation of Plant Headings

Generic entries are provided with a pronunciation guide, common name and family. Each specific epithet (the species term) has a pronunciation guide, common name, and average height and width of mature plants. The height and width are guides to help with placement in the garden. Climate, soils, rainfall, irrigation practices and fertility will influence these guidelines. The next line provides season of flowering (based on zone 5-7), flower color, origin and cold hardiness range, based on the USDA zone hardiness map.

A quick reference table is provided for genera with two or more cultivated species. Easily identifiable differences among species are listed. Descriptions for each species and known cultivars and varieties are also included. Not every cultivar or variety has found its way into the book, but ideally most of available selections are present. Related species and hybrids are then described briefly. In general, related species are not always as available to the gardening public but have worthy garden characteristics.

Descriptions such as flower color and height are based on my experience and travels and they will differ slightly from North to South and East to West. All the bad jokes and opinions are mine, made proudly and without shame. But, regardless of how opined I may be, they are still only opinions. I welcome yours.

Leaf and Flower Terminology

USDA Plant Hardiness Zone Map

A

Acaena (a-sane' a)

New Zealand Bur

Rosaceae

Of the 100 species in this genus, we are lucky to see a half a dozen in even the better public gardens in North America. As the common name suggests, many species are native to New Zealand, including its namesake, A. novae-zelandiae. Other common names for this plant are much more alliterative and any plant with names like pirripirri bur, bidgee-widgee and biddy biddy is probably worth the price of purchase alone. The excellent plantings one sees in New Zealand and throughout the British Isles have not made the transition to the North American garden particularly well. Being native to New Zealand generally equates to sure and rapid death for eastern and southern gardeners, but a reasonable chance of success for West Coasters. Nevertheless, where conditions are favorable, the dense, 2-3" tall mat-forming plants make attractive ground covers and are highly sought after.

Some gardeners find them a little too aggressive (some lucky gardeners call them thugs), as plants can take over significant areas of the rock garden or small border. They root at the nodes and are excellent for placing between stepping stones or trailing over walls. All species prefer full sun, although A. microphylla, rosy-spined New Zealand bur, A. inermis, spineless acaena, and its cultivar ‘Purpurea’ and A. myriophylla, fern-leaved New Zealand bur, are more shade tolerant than others. All species prefer low humidity and excellent drainage and are cold hardy to about 10°F (zones 7-8), although some sources have them hardy to zone 6.

In general, the flowers are not particularly noticeable, being small, greenish and lacking petals (apetalous). However, the pea-green to steel-blue leaves are pinnately compound and often finely serrated, and colorful bur-like fruit (achenes) keep gardeners wanting more. The burs are carried well above the foliage and are the most interesting part of the plants. Most leaves are about 2" long but A. myriophylla has 6-8 long green leaves with 15-17 leaflets with burs held at the end of the 6-9 flower stems. The spherical burs are often spiny and brightly colored relative to the foliage.

The more burs I see, the more I would like to see selection work done to enhance their tolerance to real weather. Hardiness is always a topic of discussion for those few people who know about these plants. Most books suggest zone 7 for cold hardiness, but Arrowhead Alpines in Fowlerville, Michigan (zone 5) says that A. inermis ‘Purpurea’ is hardy and nearly indestructible here. ‘Blue Haze’ seems to be fairly tolerant, but I have managed to kill it in my Athens garden. The vigor of A. fissistipula is well known and if crossed with blue foliage forms might provide some potentially tough, handsome offspring. Many other combinations await the bur breeder.

Propagation is usually by division, but cuttings and seed are also used. Seed should be sown in open containers in the fall, and placed in cold frames over winter.

-anserinifolia (an-sir-in-i-foe' lee-a)

Bronze Pirri-Pirri Bur

2-4/10

Spring

Rose

New Zealand

Zones 7b-9

This species bears dull green hairy leaves which are paler green beneath, and bronze or red fruit. Five to eight pairs of leaflets are tinged with pink and the combination is handsome indeed. The species is seldom offered but ‘Bronzette’, a cross with A. novae-zelandiae, is occasionally found. Plants have bronze fruit and green-bronze foliage and grow about 6" tall.

-microphylla (mike' ro-fil-ah)

Rosy-spined New Zealand Bur

2-4/12

Spring

Dull Rose

New Zealand

Zones 7-9

The short plant has small silver-blue to blue-green compound leaves with a strong hint of copper and makes an exceptionally good ground cover. The flowers are rather forgettable but the handsome pink to rosy red fruit, nearly an inch across, looks like a spiny wicked thing, but is in fact quite soft. Plants are a little more cold hardy and more tolerant of poorly-drained soils than other species. If conditions are right, it can be quite aggressive.

Cultivars:

‘Copper Carpet’ is about 2" tall with copper-bronze foliage and showy red burs.

‘Pewter Carpet’ is similar to the above but with a dull glaze to the foliage.

‘Pulchella’ is about 4" tall, with coppery foliage bearing hints of silver. The fruit is reddish-brown.

Related Species:

A. buchananii is sometimes offered by specialist nurseries and bears pea-green, 3" long leaves and amber burs. The leaflets, which occur in 3-6 pairs, are about an inch long and have soft silky margins on the underside.

A. inermis produces mats of low-growing foliage but has a smooth, rather than a spiny bur. Less fun, but more huggable.

A. saccaticupula ‘Blue Haze’ is still one of the most popular cultivars for the bur gardener. The leaves are a beautiful glaucous blue and the brownish red flowers and red fruit are handsome as well. Plants are 2-4" tall, spread well, and make attractive ground covers.

Confusion:

I often confuse plants of Acaena with Leptinella (which see), known as brass buttons, particularly when flowers or fruit are not present. They are both low, fernlike ground covers, both can have dark green foliage and both are made for rock gardens and even for walking upon. The flowers and fruit however are obviously different; Acaena is grown for the large ornamental fruit and not the rather inconspicuous flower, while Leptinella is grown for the opposite reasons, the fruit is unexciting. They are in very different families and are not really confusing if they are seen together in flower, but let’s get real here, do you really think anyone actually plants burs and buttons together?

Acantholimon (a-kanth-o-lee' mon)

Prickly Thrift

Plumbaginaceae

This large group of plants (about 120 species) occurs predominantly in rocky, high altitude habitats and thus you would not expect to see grand swaths in St. Louis or Atlanta. The genus, however, has a loyal, if small, following among gardeners. Plants are becoming better known in the North where rock gardens and alpine gardens are reasonably common. They are evergreen and grow in dense clumps of short, prickly 3-angled narrow leaves. They look like they belong more to the cactus family than the plumbago family, that is, until they flower, at which time the resemblance to the latter is obvious. To be brutally honest, when not in flower, plants resemble green hedgehogs stuck in the middle of a garden. They are slow growing, but when they produce those long-lasting sprays of small pink flowers, they can be quite irresistible.

Plants are well known by alpine enthusiasts but alpine people are by definition somewhat strange, so this should not be surprising. While these plants will always be thought of as weird, they should be looked upon by other gardeners as exceptionally good subjects for the xeric garden. They need to be used far more often in areas of low rainfall and poor soils.

It is still difficult to find Acantholimon in the trade and gardeners are often forced to raise plants from seeds or softwood cuttings. However, hope is on the way, as species such as A. glumaceum, with bright rosy pink flowers, A. olivieri, with whitish pink flowers held well above the mat, and A. ulicinum, with hot pink flowers, are becoming better known. One nursery provides 6 distinct taxa while another lists 20 taxa of Acantholimon, once again verifying that there is simply no accounting for taste in American gardening.

Cuttings can be gingerly obtained from other enthusiasts. They can be painful, so root with care. Rooting near the base of the plant is encouraged by spreading sand around the base.

All species need gritty soils but may be grown on dry stone wall, gravel beds or sunny slopes with stony soils. Areas of high rainfall may not be a problem as long as drainage is impeccable. Full sun and cool nights are necessary. An excellent collection is in the alpine garden at the Denver Botanic Garden, but private collections are also well worth searching out.

Acanthus (a-kanth' us)

Bear’s Breeches

Acanthaceae

The genus contains approximately 30 species of which three or four are particularly ornamental, providing foliage of great beauty and statuesque flowers. The basal leaves are simple, opposite, and often have soft, thorny margins. The flowers are held in long, erect spikes and each flower is subtended by a showy, spiny, leaflike bract. The spikes are lovely, albeit somewhat unnerving, but the true ornamental value of the genus resides in the handsome foliage. Once established, Acanthus is almost indestructible and will colonize an area with its invasive roots. If one tires of bear’s breeches and wishes to remove same, it is next to impossible not to leave some root pieces behind, which, like amoebae, will regenerate and recolonize their old homesite.

I have always wondered where the name bear’s breeches came from, for the combination of the two words makes no sense at all, and it is difficult to even imagine a pair of bear’s breeches. Nowhere could I find an explanation, therefore I felt much better when I learned that the eminent British horticulturist Graham Stuart Thomas was equally stumped. He contacted Professor William Stearn who shed some possible light on the subject. Professor Stearn believed that the term resulted from a confusion of the medieval Latin description "branca ursina, meaning bear’s claw. The upper part of the hooded flower, upon proper squinting, could be said to resemble a bear’s claw. But the breeches, where did they come from? Madame Audrey Serreau, a gardener from Pultiers, France, believes that additional confusion between two Latin words resulted in the breeches. The word branca which means claw, was confused with the old Gaul word braca which later became braies and finally breeches. Is this clear yet? Such explanations may be confusing in themselves, however, as Madame Serreau stated, Isn’t it fascinating to reflect upon such word changes, bringing, as they do across the centuries, echoes of long-silenced voices?"

Acanthus is popular throughout the country although most authors state that it is insufficiently hardy for much of the North. Those authors need to see the wonderful plantings in Gardenview, Henry Ross’s fine horticultural park in Strongsville, Ohio (zone 6). And if they need other proof of toughness, they should visit the wonderful garden of Dale and Lila Critz in Savannah, Georgia, where heat, humidity and acanthus are all doing well. Persistent, long-lived and certainly weather hardy.

The leaves are hardier than the flowers, and foliage may survive in particularly cold winters, but plants may not flower. Plants do well in full sun or partial shade and are relatively drought resistant although leaves will wilt often. Poor drainage is synonymous with poor performance and death. The foliage is occasionally evergreen in the South, but in severe winters becomes tattered and torn. In the North, plants are deciduous.

The most effective means of propagation is by 2-3" long root cuttings taken in the spring. Insert vertically in a well-drained medium and keep moist and warm. Shoots appear in 3-5 weeks. In the garden, I can attest to the wonders of my handy-dandy tiller, with which I inadvertently tilled up a dormant patch of A. spinosus. Next spring, every little mangled piece had sprouted. Plants may also be divided in early spring but adequate moisture is necessary to insure establishment. Fresh seed germinates in about 3 weeks if kept moist and warm (70-75°F).

Quick Reference to Acanthus Species

-hungaricus (hun-gar' i-cus)

Balkan Bear’s Breeches

36-60/36

Spring

Purple

Balkan Countries, Romania

Zones 5-9

Sold under the names of A. balcanicus and A. longifolius, plants are also similar in habit and flower to A. mollis. The dull green leaves are lobed with wide gaps between the lobes (the gap is referred to as a sinus). The sinuses are connected to each other with a flange of leaf parallel to the midrib. The sinuses are deep and the lobes are tapered at the base, characteristics which distinguish it from A. mollis. The flower stems rise an additional 3-4' and bear numerous white and purple flowers in mid to late summer. The bracts surrounding the flowers have 5-7 veins and are painfully sharp. Plants are taller than most species, and the leaves more deeply cut. The foliage is more winter hardy than the flowers. After particularly cold winters, the leaves may emerge in the spring but no flowers may occur.

Plants perform well in most gardens and since they are native to the Balkans, Romania and northern Yugoslavia, are probably the most cold hardy. They also perform better in southeastern gardens than A. mollis.

-mollis (mol' lis)

Common Bear’s Breeches

30-48/36

Late Spring

Purple

Southern Europe

Zones 7-9

In the fifth century B.C., one of the species of Acanthus was immortalized in the design of the sculptured leaves on Greek Corinthian columns. Some historians believe the design to be based on this species, others believe it is based on the foliage of A. spinosus. The lustrous green, 8-12" wide foliage is lobed but not as deeply as A. hungaricus. Although small, soft spines are borne at the end of the lobes, the foliage does not feel at all spiny. The flowers are similar to those of A. hungaricus. The plants, having a spread of up to 3', are best used as specimens or in groups of 3 to 5 plants. I have grown a number of species in the heat of north Georgia (zone 7b) and this one has flowered poorly. The magnificent plantings seen in southern California can not be duplicated in hot, humid weather.

Cultivars:

‘Albus’ has mostly white flowers.

‘Hollard’s Gold’ was originally sold in this country in 1994. The foliage is chartreuse; not bright enough to brag on its beauty but yellow enough to think about a need for fertility. Nevertheless I like this plant, even though it is not as vigorous as the species and tends to disappear in inclement conditions, like my garden. Plants are often sold as ‘Fielding Gold’, as it originally came from Fielding, New Zealand.

var. latifolius is most common although less free flowering than the species. Plants bear 3-5' tall stalks of mauve-pink flowers and glossy green arching leaves which are sometimes scarcely dissected. Plants appear to be more robust and more cold tolerant than the species. There are a number of similar forms, and plants are often classified as Laterifolius Group.

‘Rue Ledan’ was found in Matignon, France in the early 1990s. It is an excellent cultivar growing about 3' tall and producing shiny green leaves. The flowers are white rather than purple, and essentially sterile. It likely belongs to the Laterifolius Group.

‘Tasmanian Angel’ is the first variegated acanthus and should be a hit. Plants also produce really wonderful pink and cream colored flowers on 4' tall stems. The foliage is unique in that the leaves have creamy yellow irregular margins. During the summer, the leaves may revert to green.

-spinosus (spine-o' sus)

Spiny Bear’s Breeches

36-48/36

Late Spring

Mauve

Southern Europe

Zones 6-10

The main difference between this species and the previous is the presence of spiny leaf margins which look a good deal more lethal than they really are. The 10" diameter leaves are lanceolate, and more deeply divided than those of A. mollis. The flowers are similar except that three to four veins occur on the purplish bracts rather than five to seven found in common bear’s breeches. If late freezes occur, A. mollis is killed to the ground while this species is little affected. The flowers are produced consistently each year and the leaves remain fresh all season. Plants also tolerate warm, humid summers better than the previous species, a definite advantage for southern gardeners.

Cultivars:

‘Lady Moore’ is an interesting plant occasionally seen in the British Isles but seldom in the United States. The foliage is creamy white in the spring, greening up as the weather warms up. Named for the wife of Sir Frederick Moore, former keeper of the Botanic Gardens at Glasnevin, Dublin.

var. spinosissimus can be a man-eater but taxonomists have placed other plants in this group, diluting the pain. Originally plants bore leaves which were more sharply cut than those of the species, and enjoyed only by masochists or those who could command someone else to handle such vicious plants. I have enough trouble with belligerent people, why tolerate belligerent plants? Today, sufficient variation is thought to exist among plants and they are now referred to as the Spinosissimus Group.

Related Species and Hybrids:

A. caroli-alexandri has borne other names (A. syriacus), but if you want a shorter classy plant, look for this species. Plants grow only about 18" tall and bear typical white and purple flowers. However, the leaves are deeply cut and the tips can be spiny. The bracts beneath the flowers are also painful. Nevertheless, this is an excellent selection for a smaller garden.

A. dioscoridis is 1-2' tall and has rosy pink bracts. The lanceolate leaves are petioled, gray green, and in var. dioscoridis are usually entire, perhaps with a few shallow lobes. Good drainage is essential. Native to mountainous areas of Asia Minor, it is likely hardy in zones 6-9, although not enough plants have been evaluated to provide confident hardiness ratings. var. perringii is more common, bearing deeply cut, almost spiny leaves and with more pink in the bracts.

‘Summer Beauty’ is likely a hybrid between A. mollis and A. spinosus. The leaves are more deeply cut than A. mollis but are still shiny and handsome. The plants are vigorous, 4-5' tall and bear white flowers with purple bracts. This is far superior than either of the parents, and I rate it highly.

Achillea (a-kill' ee-a)

Yarrow

Asteraceae

Although there are approximately 100 species, fewer than a dozen are truly ornamental. They range in height from four inches (A. nana) to four feet (A. filipendulina) and provide flowers of almost every hue. Leaves of all species are alternate and, with the exception of A. ageratum, sweet yarrow, and A. ptarmica, sneezewort, the foliage is deeply divided into a fine fernlike appearance. In several species, the foliage has a heavy spicy odor and a gray-green tint. A member of the aster family, its heads are made up of two distinct types of flowers. The outer ray flowers are pistillate (female only), and may be yellow, white, or pink while the inner disc flowers are bisexual (male and female together), and usually yellow. The flower heads (inflorescences) look like small table tops called corymbs. Another advantage of growing yarrow is the gardener’s ability to cut the flowers and enjoy them indoors. The flowers of most species make excellent fresh or dried specimens but the pollen must be visible before the flowers are cut or vase life will essentially be nil.

Some yarrows are at times considered weeds, particularly those which multiply rapidly from invasive rhizomes. This characteristic, however, is true for only one or two species; most others behave themselves and stay at home. Unless otherwise noted, all species should be grown in full sun and well-drained soils. They tolerate poor, slightly acid soils (if well-drained), although A. clavennae performs well in limey soils. Do not fertilize yarrows heavily; many of the upright species will grow too tall and lanky if fertilized or grown in rich soil.

Quick Reference to Achillea Species

-‘Coronation Gold’

Coronation Gold Yarrow

2-4'/3'

Late Spring

Yellow

Hybrid origin

Zones 3-9

This hybrid was first offered in 1953 by Miss Pole of Lye End Nursery in southern England to commemorate the coronation of Elizabeth II. An amateur hybridizer, she crossed A. filipendulina with A. clypeolata, a small yellow-flowered species, to raise the best upright golden yellow yarrow available at that time, and arguably, still the best today. Plants were subsequently sold and distributed by Blooms of Bressingham of Diss, England and rapidly became popular throughout the world. It is sometimes incorrectly listed as a cultivar of fern-leaf yarrow, A. filipendulina, but that is unfair to this excellent hybrid.

The plant is shorter than A. filipendulina, better branched, and does not require staking. It requires less maintenance and should be the plant of choice for landscapers. The inflorescences are 3-4" across and look like shiny golden plates. Flowering begins in late May in north Georgia, June in the Northeast, late June in the Midwest, and continues for 8-12 weeks. The foliage is gray-green and has a strong aromatic smell. It tolerates a wide range of climates and soils and is grown in gardens from Manitoba to Florida.

‘Coronation Gold’ is also popular as a cut flower throughout the world. It is interesting to note the differences in stem and flower size between northern and southern climates. In north Georgia, over 50 flowering stems per plant were produced while the same plants growing in Holland yielded fewer than 15 stems but each one was 1 1/2-2 times longer with larger flowers. Propagate by terminal cuttings in spring or early summer, or by spring or fall division every 3-4 years. Stay away from seed labeled ‘Coronation Gold’; it will likely be A. filipendulina or one of its cultivars.

-filipendulina (fi-li-pen-dew' lye-na)

Fern-leaf Yarrow

3-5'/3'

Summer

Yellow

Caucasus

Zones 3-8

The foliage is deeply cut and feathery but bears little of the gray-green tint that is so appealing in ‘Coronation Gold’. In general, foliage is greener, flowers are larger and plants are taller than those of ‘Coronation Gold’. This is a wonderfully handsome plant but when grown in rich soils, warm temperatures or over-fertilized, it generally requires staking, a job most sane people view with disdain. The flat yellow flower heads are 3-4" across and make excellent cut flowers. Provide full sun. Yellow-flowered yarrows combine well with pink phlox, purple-foliaged plants, blue delphiniums and red hot pokers.

Achillea filipendulina

Plants may be propagated by spring division, terminal cuttings in early summer, or by seed. Seed sown in a mixture of 1:1 peat:vermiculite and placed at 70-72°F in a humid area germinates within 21 days. Most cultivars are available from seed.

Cultivars and Hybrids:

‘Altgold’ stands about 3' tall and bears deep yellow flowers in late spring and again in early fall. An interesting rebloomer.

‘Cloth of Gold’ bears large pure yellow flowers and grows 3-4' tall.

‘Flowers of Sulphur’ is a 2' tall, slow-spreading hybrid of A. filipendulina and A. ptarmica. One of the best sulphur-colored flowers in the genus.

‘Gold Coin’ is a dwarf form of ‘Parker’s Variety’, and grows only about 15" tall.

‘Gold Plate’ has deep yellow flowers on stems up to 5' tall.

‘Parker’s Variety’ bears golden yellow flowers on 3-4' tall stems. This one and ‘Gold Plate’ produce large numbers of flowers and have better stem strength than the species but may require support in areas with hot, humid summers.

‘Schwellenburg’ is likely a hybrid with A. filipendulina and a yet to be determined species. The golden flowers sit atop silvery, ferny foliage and stand 1 1/2-2' tall. Plants do not appear to be particularly vigorous or tolerant of adverse weather, however if old flowers are removed and plants are not over-fertilized, better results can be expected.

-millefolium (mil-lee-fo' lee-um)

Common Yarrow

1-2'/5'

Summer

White to Cerise Red

Europe

Zones 3-9

Common yarrow is common because of its ability to spread rapidly and take over any ground available. Often seeded as a wildflower on roadsides, the ferny foliage and off-white flowers fill in median strips and combine well with other roadside plants such as bachelor’s buttons and poppies. In Europe, it is often discarded as a troublesome weed not to be included on the grounds of any self-respecting gardener. Yet the same people will find fresh and dried flowers of common yarrow in florist shops where they are widely used in colorful bouquets. The species was cultivated in Europe before 1440, used as a remedy for toothache, and mixed in ale in place of hops to increase the inebriating quality of that drink. It was thought to have a magical quality similar to our apple a day keeps the doctor away; and was said to grow in churchyards as a reproach to the dead, who need never have come there if they had taken their yarrow broth faithfully every day while living. The main use, however, was that of an herb to heal wounds. The genus was named after Achilles, who is said to have used A. millefolium to staunch the wounds of his soldiers, thus acquiring the common name of soldier’s woundweed and woundwort. And everyone thought this was just a common old flower!

Achillea millefolium

The habit is matlike and the dark green foliage is deeply cut. In early summer, the flower stalks rise about two feet and are quite strong where night temperatures consistently stay below 70°F. Where night temperatures are too warm, the stems do not acquire enough carbohydrates to fatten up and topple. Plants fill in rapidly and those placed four feet apart produce an unbroken mat in 2 years. If planted two feet apart, they fill in by the end of the first year.

A number of cultivars are offered from seed but it is just as easy to divide good specimens to retain the desired colors.

Cultivars:

Some of the following are selections of A. millefolium, many are hybrids. Most of the hybrids are of questionable parentage but all have A. millefolium in them. The Galaxy hybrids (A. aegyptiaca var. taygetea (formerly A. ‘Taygetea’) x A. millefolium) have similar foliage to that of A. millefolium but the flower heads are larger and the stems much stronger. The only problem I have seen is the tendency of the flowers to fade, particularly when temperatures are above 80°F. In our trials in north Georgia, ‘Beacon’ and ‘Great Expectations’ faded less than others. In climates with cool night temperatures, little fading is seen.

‘Appleblossom’ is a vigorous 3' tall plant with peach to lilac-pink flowers. A Galaxy hybrid.

‘Apricot Beauty’ is likely a hybrid. It is difficult to find in this country but with its flat-topped soft yellow to apricot flower heads, it should be more common.

‘Apricot Delight’, ‘Strawberry Seduction’, and ‘Wonderful Wampee’ are part of the Tutti-Frutti series of seed-grown yarrows, designed primarily for rapid greenhouse production. And, no, I have no idea what they were smoking when these names were selected. Flower colors are light apricot, rose and light pink, respectively. All stand 12-20" tall, the former being the shortest and the seducer being the tallest.

‘Belle Epoque’ has dusky pink flowers and gray green leaves. Plants earned an Award of Garden Merit (1999) from the Royal Horticultural Society.

‘Borealis’ (var. borealis) bears dense clusters of rose-pink flowers.

‘Cassis’ is about 2' tall with flat heads of cherry-red flowers. Plants bloom first year from seed.

‘Cerise Queen’ is one of the oldest and still popular cultivars. Plants are grown for the cerise-red flowers. It grows about 18" tall and provides bright drifts of color.

Achillea Galaxy hybrid

‘Chamois’ has interesting tan-colored flowers (like a chamois?) which fade somewhat to a creamy yellow. Sounds awful, but not so bad.

‘Christel’ is a relatively new hybrid, with deeper green foliage than most millefolium forms. The flowers are deep rose-pink and if cut back may rebloom.

‘Christine’ has fernlike foliage, grows about 2' tall and is topped with light rose flowers.

‘Citronella’ bears butter yellow flowers on an erect habit.

Colorado mix is grown from seed and provides flowers in a wide range of colors, including apricot, pink, red, russet, yellow, apricot, pink, and cream.

‘Creamy’ bears large heads of creamy-yellow flowers. Plants fill in quickly.

‘Credo’ was bred in Germany, resulting from A. filipendula x A. millefolium. It is a tall (3-4') cultivar with light yellow flowers that tend to fade to creamy-white. Good for cut flowers.

‘Debutante’ is a mixture of plants, bearing rose to creamy white flowers. ‘Pink Debutante’ is also an excellent selection.

‘Fire King’ and ‘Fire Beauty’ have dark red flowers; there is little difference between them.

‘Fireland’ opens red then fades to pink and finally to a tawny gold. The plants grow about 3' tall but the stems are reasonably stout.

‘Great Expectations’ (‘Hope’) produces primrose yellow flowers on 2' high stems. A Galaxy hybrid.

‘Heidi’ has pastel pink flowers on 20" stems in the spring and reblooms a little later in the summer.

‘Hidden Pond Pink’ is a silly name for a pink-flowered, relatively short (15-24") yarrow.

‘Island Pink’ has deep pink flowers and a deep green foliar color.

‘Jambo’ bears medium yellow flowers on 15-18" tall stems.

‘Jungfrau’ has pastel yellow, almost white, flowers on 15" plants.

‘Kelwayi’ bears magenta-red flowers on 18" stems.

‘Lansdorferglut’ is an ugly name for a pretty 2-3' tall plant with soft pink flowers in flattened heads. Good for cutting.

‘Lilac Beauty’ produces lilac flowers on strong upright stems.

‘Lilac Queen’ has flat heads of pastel lilac flowers and is offered occasionally by mail order nurseries.

‘Lusaka’ has white flowers and is a vigorous grower. ‘Madelein’ bears apricot colored flowers on 2' tall plants.

‘Martina’ has large, flat yellow flower heads on 2-2 1/2' tall stems. The foliage is ferny and green.

‘Marmalade’ has flowers in autumn colors of dark yellow and orange.

‘Mary Ann’ bears lemon-yellow flowers over silvery-gray foliage and grows only about a foot tall.

‘Maskarade’ produces interesting pale yellow flower heads with red flecks along the edges as they mature. Quite a different look.

‘Moneymaker’ has salmon-pink flowers. I’m not sure where the money will be made, as there are many others with similar flower color as well.

‘Nakuru’ produces purple and white bicolor flowers.

‘Natalie’ is 2-3' tall with light pink flowers.

‘Orange Queen’ has unusual orange-gold flowers. About 30 tall and 18 wide.

‘Paprika’ produces red and yellow flowers on a flattened inflorescence. One of the most handsome cultivars available.

‘Petra’ resulted from a cross between ‘Credo’ and ‘Fanal’. Plants bear fiery red flowers and stand about 20" tall. Plants are unique because they are sterile and no wishy-washy seedlings will