West Coast gardens continually fill with new and exotic perennials from around the world. Some are big, bold, and beautiful, demanding our attention and admiration, while others are more demure, hiding in the shadows, quietly waiting for the spotlight to shine on them. The time has come for one of these new stars, the genus Impatiens, often called balsams and formerly regarded as filler for annual beds, to be illuminated on the perennial garden stage. At the San Francisco Botanical Gardens at Strybing Arboretum, we are introducing more of these exotic plants, which most gardeners have never seen and would likely not guess were Impatiens at all. The San Francisco Bay Area provides the most suitable climate for many species: the cool, foggy summers and relatively mild winters allow even the frost-tender species to flourish.
Of the nearly 1,000 species of Impatiens, the greatest concentration occurs in Asia, mainly China, the Himalayas, India, Southeast Asia, and on the neighboring islands. Africa and Madagascar boast a goodly number, with nearly 300 between them. Only one species is native to Europe, and about six to North America; there are none in Australia or South America. The generic name comes from the explosive (impatient) nature of the seedpods; when ripe, the slightest touch will cause the fruits to fling their seeds as far as twenty feet away. Most species are quiet foliage plants, blending into their surroundings. Their flowers, however, set them apart.
Like the flowers of orchids, with which they are often compared, Impatiens flowers also cater to a particular pollinator and are resupinate (what looks like the top banner petal is actually the bottom one, the pedicel having twisted as the flower opens). The flowers have five petals, but the two lateral petals are joined and can appear as one large petal. Most species have only three sepals, but a few have a full set of five. The lower sepal is often enlarged into a nectar-filled spur. The five stamens wrap around the pistil like a tiny five-armed octopus. As the female organ matures, it begins to expand, breaking the grip of the stamens and causing them to fall. The whole reproductive structure is shaped like a column, as in some orchids, held over the mouth of the spur. Whatever pollinator enters this opening, be it a bird’s beak or an insect’s body, must pass this structure to reach its reward of nectar, thereby picking up pollen or depositing some on the stigma.
Most balsams originate in the cool tropical highlands of the Old World. Such places are virtual islands surrounded by a sea of heat at the lower elevations. This has caused many closely related species to become isolated from one another, resulting in a good deal of speciation within the genus; some species are endemic to only one mountain and occur nowhere else. Many species are on the edge of extinction, as human populations impact on their habitat.
Although the familiar bedding species of Impatiens (I. balsamina and I. walleriana), are tender plants succumbing to the slightest frost, some of the species now being introduced are hardy perennials able to survive the winter temperatures experienced in USDA hardiness zone 6 (-10° to 0°F). Many hardier species come from Asia and Africa and have a rhizomatous or tuberous root system that can more easily survive such cold winters.
An Early Introduction
In 1983, Don Jacobs of Eco-Gardens (Decatur, GA) introduced Impatiens omeiana ‘Eco Hardy’, a selection from Emei Shan (Mt Omei) in Sichuan, China. Hardy to USDA zone 6, this species grows from a creeping rhizome and, when happy, spreads easily. Unlike the flat-faced flowers of the “old-fashioned” bedding species, the flowers of this attractive plant are rather long, fat, yellow tubes, flared at the mouth—resembling a strange fish. The lanceolate leaves add to this balsam’s appeal. In shade, striking yellow markings appear in the center of the leaves; the deeper the shade, the richer the color. The leaf edges may also develop a bluish cast. To the untrained eye, ‘Eco Hardy’ might look like one of the New Guinea hybrid impatiens (also known for their colorful foliage) until it reveals itself in bloom.
Impatiens omeiana ‘Ice Storm’ is a cultivar I introduced from England. In its basic form, this is similar to ‘Eco Hardy’ though somewhat larger, with pale yellow flowers. The leaves on ‘Ice Storm’ have a distinctive silver crackling effect on the upper surface, as if covered with a thin layer of ice. This feature is strongest in the spring when the first new leaves emerge and the crisp cool air brings out the brilliant colors. Christopher Grey-Wilson, one of the botanical gurus of the Impatiens world, recently confirmed this to be a selection of I. omeiana. I had initially called it I. omeiana affinis, under which name it can still be found.
Many of the hardy Asian species appear to form a close relationship with Impatiens omeiana. One is a Heronswood introduction (#DJHC 98415), a still undescribed species collected by Dan Hinkley on his trip to Emei Shan in 1998. When not in flower, I. ‘Heronswood’ looks rather like a plain green-leafed form of I. omeiana, but, as the summer cools, it clearly stands apart with its delicate shell-pink flowers and long tapering spur. The two upper lateral sepals curl ever so slightly giving it a fanciful charm. So far this species has been rather slow for me and a little shy to flower.
I passed up an early opportunity to acquire Impatiens ‘Milo’, thinking it was yet another I. omeiana, since that was how it was listed by the Chinese nursery that offered it. Bjornar Olsen, a fellow impatiens collector from Norway, inquired about its identification, which led to my researching the plant. I was astounded when I saw its picture. Other than having a rhizomatous habit like that of I. omeiana, the plant is totally different. Impatiens ‘Milo’ is more shrub-like, to about two feet tall, with large, pale green, ovate fuzzy leaves. The flowers have the look of delicate sea creatures swimming amongst the foliage. They are a soft pink to almost white, with the upper petal curiously mounted with two horns, like a rhinoceros. The large lower petals provide a perfect landing platform for incoming bees. The interior of the flower is spotted and lined with salmon blush tones. The inside of the elegantly curved spur is striped in red, which shows through as faint lines of rose on the outside.
Blue is a rare color in the plant kingdom and rarer still in Impatiens. With flowers falling more in the purple range, I. arguta comes close. A widespread species in nature, it was only brought into cultivation recently. Native to the southern parts of Asia, including Nepal, it is one the hardiest balsams around, said to tolerate winter temperatures down to the single digits (surviving by its tuberous roots) and summer temperatures into the 100s (when most other impatiens wither away). That is an impressive range for any balsam and helps make it one of my favorite species. In early spring, the plant is not much different from any other perennial with its dark green puckered leaves and deep red stems. As temperatures warm in late spring, the flowers begin to appear, slightly hidden under the leaves but peeking out enough to make you look closer.
With its widespread range, it’s not surprising that there are some interesting variations. One is Impatiens arguta ‘Alba’, offering a white flower with a pink horn on the upper petal. I am still trialing this one; it did not die down at all last winter, sheltered under an evergreen tree. Another selection with promise is a strongly upright form, I. arguta affinis, which may yet prove to be another species. It reaches nearly three feet tall, with pale green stems, pale bluish petals, and a white sepal and spur. This is the only hardy perennial impatiens that has set seed for me; it also has died completely to the ground, where the others have stayed somewhat evergreen in my Sacramento garden (USDA zone 9, Sunset zone 14).
Another Nepalese native, Impatiens puberula requires only a little imagination to resemble a fancy, long-necked bird. Mostly purple, it does have some blue shading near the center of the flower’s throat. The exact hardiness is unknown, but it has sailed through winters along the western coast of Wales (roughly USDA zone 8) and should survive lower temperatures because of its tuberous root. It has a low spreading habit.
For the major breeders, the ultimate goal is a true blue-flowered, bedding-type balsam. The introduction of Impatiens namchabarwensis, may soon fulfill this dream. With flowers described as ultramarine blue, this species is a great addition to the garden palette. Described as recently as December, 2005, it comes from Tibet’s Namchabarwa Canyon, said to be twice as deep as the Grand Canyon. Impatiens namchabarwensis is closely related to I. arguta but is easily distinguished from it by its heavily serrated leaves, similar to those of a currant (Ribes). It will take the garden world by storm, for it is of easy culture and sets seed readily. Like I. arguta, it seems to do better in warmer conditions.
Two closely related Himalayan species are Impatiens stenantha and I. longiloba. Both have yellow flowers that are slightly twisted, with a spur that curves up like a gnome’s cap. Of the two, I. stenantha shows the most garden potential. It has a compact habit, six inches in height, with deep bronzy green, ovate leaves; its cheery yellow and red flowers sit just above the foliage. This particular clone came to me via Ray Morgan, the Impatiens National Collection holder in Wales, from a Scottish gardener, who brought it back from Asia where he lived over thirty years ago. It should be hardy since it has been living in a Scottish garden for three decades. Impatiens longiloba, on the other hand, is still being trialed. It is a much taller plant, reaching nearly two feet; its pure yellow flowers are similar, but the spur has a less pronounced upward curve than on I. stenantha. Both species seem happier and more floriferous in my garden during the cooler spring and fall seasons.
Given the tremendous plant diversity on the island of Taiwan, one might expect more than just three native species of Impatiens. Of the three, the only one in cultivation is Impatiens uniflora. The island’s location within the tropics suggests that its balsams would not be particularly hardy, but the botanical world is full of surprises: I. uniflora is perfectly happy in USDA zone 7. Its thin stems and small, ovate, deep green leaves give I. uniflora a more delicate appearance than that of I. omeiana. Pink and white flowers are reminiscent of its Himalayan annual cousin, I. balfourii, which also makes a first rate garden plant, only too happy to seed itself around any garden.
A Few from Africa
When I first became interested in impatiens, the Holy Grail of my search was Impatiens tinctoria, a native of eastern Africa. The largest of the hardy perennial balsams, it reaches nearly eight feet in ideal conditions. Its only challenger is the prolific I. glandulifera, an annual. Impatiens tinctoria was impossible to find in the US, but I eventually located it in England. It arrived as such a small tuber that I held scant hope for its success. Happily, it grew quickly into a plant large enough to share with several mail-order nurseries on the West Coast. The three-inch, red-throated, white flowers possess a strong gardenia scent and appear during the cool summers of the San Francisco Bay Area. Unfortunately, the summer heat in the Sacramento Valley delays its flowering until fall. This species has an open habit with only a handful of stems rising from its dahlia-like tuber. In frost-free gardens, the stems do not die but lean over until a node touches the ground where it sends out roots to make a new clump—a walking perennial. It is best planted as a background specimen, perhaps among a group of smaller flowering plants or ferns whose foliage might afford it some winter protection in colder regions.
A number of African species form tubers like Impatiens tinctoria but only a few are in cultivation. Two now being trialed are the closely related I. flanaganae and I. fischeri. Their floral structures are rather similar, though I. flanaganae has large pink blooms whereas those of I. fischeri are much smaller and red. Both seem reluctant to flower when temperatures are high. Impatiens flanaganae, unlike its cousin, has a definite dormancy period; it reaches a height of four feet with eight-inch ovate leaves. Although it comes from low elevations, it is native to a cool forested coastal area along the St John’s River in Natal. Impatiens fischeri has no dormancy period and grows all year long. Originally described as tuberous, it actually has above ground runners, with which it spreads readily. This species comes from high elevations, like that of I. tinctoria, but is more frost tender, surviving only in sheltered areas of USDA zone 9. During the winter, it will put on a show of small red flowers that seem to hover above the glossy ovate leaves.
At Home in the Garden
All of these species of Impatiens are easy to cultivate and many make wonderful ground covers. In their native habitats, most grow in the loose leafy soil of the forest floor, making beautiful colonies. In the garden, it can be a different story: in heavier soils, the running balsams spread more slowly and do not compete well with other plants that might over- shadow them. I have seen an entire colony of I. omeiana die out from crowding by other plants. Heavy soil may also cause tuberous species to rot from lack of drainage. The soil can always be amended to provide a looser, humus-rich structure. High shade, cool and moist, will do them well. Be sure to keep openings in the planting for them. With these steps in mind, Impatiens will fill their spots and grow to their full potential.
While Impatiens may not be good candidates for a drought-tolerant landscape, the beauty of the genus cannot be denied. They fill the garden with a bounty of exotic blooms and vivid colors that few garden plants can match. With the destruction of the rain forests and the limited areas that Impatiens come from, it would be sad to see them disappear from the world stage— never to have graced our gardens or our hearts.
Only one other genus exists in the Impatiens family (Balsaminaceae): Hydrocera, a monotypic semiaquatic species from Southeast Asia that forms berries. At one time, Impatiens was considered a part of the order Geraniales, closely related to the garden nasturtiums (Tropaeolum). With the recent genetic work done on this family, the Balsaminaceae now belong to the order Ericales, forming a group of plants called the Balsaminoids, which includes the Marcgraviaceae and Tetrameri-staceae. The Marcgraviaceae is a small New World family consisting mostly of lianas, with small flowers that hang over nectar-filled containers reminiscent of the pitchers of Nepenthes. The Tetrameristaceae consists of three or four species of trees, two from Southeast Asia and the others from Central America. One of these was once considered to be in the monotypic family Pellicieraceae, with the single genus Pelliciera, a type of mangrove tree with large jasmine- like flowers.
The explosive nature of Impatiens seed pods means that seed can easily be spread from a single planting. Several of the annual species of Impatiens can become weedy in gardens and hold the potential for escaping into moist riparian situations. As with any new plant, be watchful of any inclination to spread rampantly within and beyond the garden.
An Impatiens Resource Guide
San Francisco Botanical Garden Society
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22711 NW Gillihan Road, Portland (Sauvie
Island), OR 97231
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