10 Wonderful Weird Plants

Every garden needs a peculiar prennial–something out of the ordinary to catch the eye. Here, the senior curator of Denver Botanic Gardens shares his top 10. Maybe there's a spot for one in your garden.

When flowers come to mind, most of us think of their beauty, colors and charm. But we who work at Denver Botanic Gardens know that if you want to rivet the attention of a child, show them a Venus flytrap. Truly, the weird, wild and wonderful aspects of the plant kingdom enthrall us adults just as much. We don’t always admit—or perhaps even know—to what degree curiosity and awe of nature motivate our love of plants and gardens. There are a host of quirky plants I treasure, and would never want to be without; these do not have the fragrance of the rose, the poise of the lily, nor the majesty of a lotus on the pond. But they have ceaseless character, and never fail to enthrall me. Let me share 10 of my beloved “weirdie” plants with you:

Amethyst Sea Holly

(Eryngium amethystinum)

Eryngos are found throughout much of Eurasia and the New World, from the Caucasus Mountains in the east to Patagonia in the south. All eryngos are strangely alluring: Their foliage can be wildly incised and almost prickly; their flowers are mostly steely grays and blues. They act almost like everlastings if cut just before they’re in full bloom.

Over the years, I’ve grown dozens of species and cultivars, and have a fondness for all of them. But supreme in the genus, in my opinion, is the late-summer-blooming, amethyst-flowered sea holly. The foliage is extravagantly slashed and twisted, delightful in and of itself. But starting in August and lasting for much of the autumn, a well-established clump will sport dozens of sizeable flowers that blend violet purple, hot pink and cobalt blue in the most alluring combination. And it looks different in different lights. This irresistible plant is easily grown in a border or rock garden, and blooming as it does, at a relatively slow season for the garden, makes it a standout—albeit a rather peculiar one! 

Syrian Bear’s Breeches

(Acanthus syriaca)

The genus Acanthus possesses the stylized beauty of a Bette Davis, rather than the starlet charm of an ingénue. These plants are dowager divas of the Gardens, hoary with lore. The only common name they have in English is “Bear’s Breeches”—a rather amusing idea, if you think about it. The ancient Greeks loved Acanthus so much they used the lobed leaves’ shape as a model for molding on buildings and for the lavish Corinthian columns. Acanthus patterning persists in modern design, although few of us recognize it.

Several species are found in the leading local garden centers from time to time. Acanthus spinosus is very large and exotic, but has proved tough as well. Acanthus balcanicus (also known as A. longifolius and A. hungaricus) is especially hardy and suitably strange. But A. syriaca, which we’ve had at the Gardens for nearly 20 years now, is the most peculiar and beautiful of the genus to my eyes. It thrives in both dappled shade and full sun, forming compact clumps of prickly foliage. The flowers emerge in late May and look stunning through much of the summer, with deeply stained violet-purple bracts and creamy, face-like flowers poking out alluringly.

Funny how some plants look as though they may turn into animals and ambulate, and believe me, this is one such quasi-quadruped! A few mail-order nurseries offer this plant from time to time, and it merits the search.

Lizard Ice Plant

(Aloinopsis malherbei)

Hardy ice plants have become some of the most popular ground covers in our region over the last few decades. Most of them grow rather quickly, and spread a bit too fast for some spots. But there is a whole suite of clumping or slower-growing ice plants that are especially well suited to the rock garden or xeriscape. None are more fascinating than the genus Aloinopsis, which is practically restricted to the highest ridge tops of the interior of South Africa, where winter temperatures are very cold indeed.

The strangest and most alluring of these has to be Aloinopsis malherbei, which really does look more like a lizard than a plant. The wonderful, succulent leaves are covered with strange, warty tubercles that are rough to the touch. When the miraculous flowers come out in spring, the plant looks like Beauty and the Beast! This ice plant needs a well-drained spot in sun.

Since horned toads are a bit too exotic for our gardens, this vegetable lizard makes a great substitute. Best of all, it doesn’t bite or shoot blood out of its eyes!

Black Hollyhock

(Alcea rosea ‘Nigra’)

It’s worth doing a Google image search for this hollyhock—you’ll be amazed by how many hundreds of stunning photographs have been taken of it. Like all hollyhocks, this one thrives in almost any type of soil—from clay to sand to rich loam—provided it is not overwatered. I remember hollyhocks growing in all the alleyways of Boulder when I was a child, usually pink, white and purple ones. This unusual black selection deserves a prominent spot in the garden, and looks especially lovely combined with pale, straw-colored annual sunflowers. 

Like all hollyhocks, this plant produces a lush basal rosette of pale, gray-green seersucker leaves that persist through winter. The towering stem shoots up in spring and can reach 6 feet when happy. The flowers are sported in flushes through the summer. I have not found this hollyhock to be as susceptible to mildew as some kinds of mallows, but I would avoid too much watering in the afternoon or evening hours. Water it in the morning, so the leaves can dry out quickly. If your plants do get unsightly with mildew, just cut off and discard the affected parts—fresh new leaves will come out quickly.

In the meantime, you can marvel at the ebony sheen of the silky flowers for months on end in the summer. Nothing takes me back to childhood quicker than bees buzzing in hollyhock hoops. I wonder if children still make these into little doll dresses.

Birds of Paradise Bush 

(Caesalpinia gilliesii)

This name causes a bit of confusion; there is another bird of paradise plant (Strelitzia), commonly planted in Mediterranean climates, that comes from South Africa and is in the banana family. Our shrubby bird is in a flamboyant branch of the pea family. It has wide-open, face-like flowers that strain your credulity when you realize they are glorified beans. This bird can form a small tree in the Andean foothills of Argentina, whence it hails, and is the only shrubby South American plant to prove hardy in the Denver area thus far. The stems are not hardy in the coldest winters, however. They will often freeze to the ground and reemerge late in spring and still manage to grow 8 or 10 feet in a season.

The plant starts to produce huge panicles of strange and wonderful spidery blooms in June. The show continues right up to frost, when the flowers are augmented with big, bean-like pods decorative through the winter in their own right. Give this bush a protected microclimate in the garden—along the sunny side of a house or against a boulder, so it can endure. Although it’s planted in the open at Denver Botanic Gardens, it receives the full heat blast of the “urban island” effect.

Sugarbowls

(Clematis hirsutissima)

Most gardeners associate clematis with vines, but there are in fact several large groups of this genus that are essentially herbaceous perennials. None are more stately or magnificent than the sugarbowls found in our mountains. Clematis hirsutissima (meaning “very hairy” in Latin), has accrued no end of common names—Granny’s bonnets, bush clematis, Rocky Mountain clematis, as well as sugarbowls—indicating just how beloved this flower is amongst hikers and mountain folk. It usually comes into bloom in late April at Denver Botanic Gardens, and can still be found flowering in June throughout the foothills, where it can be a common plant among the ponderosa pines. At lower elevations Clematis hirsutissima is replaced by its close relative, C. scottii, which has a more spreading habit and greater heat tolerance.

Laporte Avenue Nursery in Fort Collins was the first wholesale and mail-order nursery to master the cultivation of C. hirsutissima, which it now distributes to garden centers throughout our region. Remember that the modest plant you receive in a 4-inch pot will produce a taproot, and can form a mound as big as a bushel basket in a few years. So be sure to provide it with the space it needs to shine.

I’m dazzled every spring when I watch the clumps of sugarbowls at Denver Botanic Gardens rise out of the ground in their woolly coats and poke their pipe-like flowers out of the hoary stems like a very slow-moving creature from the Arctic, or perhaps from a coral reef. The flowers are equaled, if not surpassed, by the show of their magnificent, glistening seed heads through the summer months. Sugarbowls are surely among our most aristocratic native plants, worth any effort to obtain and grow well. Plant it where it will stay—it gets massive with time and does not like to be disturbed.

 Haller's Pasqueflower

(Pulsatilla halleri)

I think I have taken more pictures of our native pasqueflower (Pulsatilla patens) than of almost any wildflower. Why? Because it blooms so early in spring, when we are all quite desperate for color. And, of course, it is hugely photogenic. One must always try to better one’s efforts each spring! Alas, our native species is recalcitrant in cultivation—I have only had it persist a year or two at best, and it flowers more feebly in the garden than in nature. The common European pasqueflower is wildly flamboyant and showy, but lacks the winsome charm of our native hairy beast.

But there is an easily grown pasqueflower from Eurasia—Pulsatilla halleri—that is superficially very similar to our native species in its opalescent lavender flower color. The extravagantly hairy seed heads in late spring are almost as gratifying as the flowers. Although the plant is not universally available, a local wholesale nursery is building up stock. And there are many commercial seed sources, including the North American Rock Garden Society’s famed seed list, where this is a mainstay. Each year I’m astonished by the silky, woolly flower buds emerging from the ground like some mysterious prehistoric creature—a spectacle well worth the effort to stage in your own garden.

 Woolly Mullein

(Verbascum bombyciferum)

Henry Mitchell suggested that the Latin epithet “bombyciferum” really should mean “carrying a bomb,” since this is a bombshell of a garden plant. Although technically biennial (the first year forming a huge, wonderfully woolly white rosette that is decorative in its own right), the plant will perish after the exorbitant display of flower stems the second year. I find that if you leave the seed to ripen, you are apt to have it popping up here and there in a less than perfectly tended garden. (My own verges on a wild garden, and I always have mulleins to spare!)

The flower stems on a happily growing mullein can grow 7 or even 8 feet tall, and occasionally they can bend and twist to make the most decorative of pictures in themselves. This plant is the darling of floral arrangers who practice extreme arrangements. The individual flowers are several times as big as our weedy native mullein, sometimes 2 inches across, and quite appealing up close. But it’s the overall strange display of giant rosettes and wild stems that makes this plant a showstopper in the garden. I, for one, would never dream of living without it. If you get one, you too will become a mulleinist!

 Duncecaps

(Orostachys iwarenge and Orostachys spinosa)

I’ve also heard these Oriental sedum relatives given the common name “Chinese pagoda flowers,” which is a tad more dignified, if less descriptive, than the terse and colorful “duncecaps.” The real dunce is anyone who would pass up the chance to grow these accommodating plants in their garden. I find all Orostachys compelling, and grow a dozen or more species and hybrids here and there—-every-where, in fact—in my garden. On a trip to Mongolia and Kazakhstan, I found O. spinosa growing at practically every stop we made in the Altai Mountains—in the desert, in mountain meadows and on alpine tundra. Each time we got out of the car someone would call out, “Here they are again!”

There were spots where these sedum relatives were everywhere underfoot, and we trod carefully to avoid crushing them. The photo above of O. spinosa shows a trough I planted with this species, which complements the color of the concrete rather well. The exact symmetry of the rosettes is very compelling to visitors, all of whom seem to be riveted by this container. In fact, I have been surprised to find  pictures of it in several publications.

I grow Orostachys all over my rock garden and in many containers, and once established they make a wonderful mat of ball-like foliage. The pagodas begin to form in late summer, eventually becoming a whole colony of adorable little duncecaps that persist well into winter. It is hard to imagine a more carefree and charming aggregation of plants.

Fernleaf Peony

(Paeonia tenufolia)

Few plants cause visitors greater amazement at Denver Botanic Gardens than our giant clumps of fernleaf peony next to the pavilion just inside Plantasia. For weeks on end, the misty, finely divided cloud of foliage rising in the spring is endlessly fascinating. When the pearly buds form like green marbles, visitors are curious. When the marbles turn deep red and explode into giant, satiny vermilion flowers almost 4 inches across, the gasps from visitors are clearly audible. No matter how many springs you’re blessed to see this plant’s performance art, it never prepares you for the encore!

The double form of this plant is rarely available, but when it is, the price is dear indeed (triple figures are not unheard of). But the wonderful single form, every bit as graceful, is sold by the best garden centers in the Denver/Boulder area for a very reasonable cost each spring. I have three sizeable clumps in my home garden, and I am not sure that is enough! Few plants embody the beauty of the steppes of Asia more dramatically than this floral centerfold of a peony.

Panayoti Kelaidis is senior curator and director of outreach at Denver Botanic Gardens.