Lewisia: Alpines Gems of North America
(Editor's Note: This article was originally published on June 5, 2008.)
Lewisia are probably among the top 10 alpines plants grown (or wanting to be grown) by rock garden enthusiasts. While alpine gentians may be the ultimate symbol for alpine gardens in Europe, Lewisia may serve the same role in North America. The genus Lewisia (family Portulacaceae) was described by Frederick Pursh in his Flora Americae Septentrionalis (Western American Flora) in 1814, based on specimens collected by Captain Meriwether Lewis during the famous Lewis and Clarke expedition to western United States (the genus Clarkia was named in honour of Clarke). The first described species was L. rediviva.
There are 19 species of Lewisia, all native to western North America. The most popular species have large, very showy flowers and include the two most well-known species, L. cotyleon and L. tweedyi. Several have smaller flowers but are not without their charm. Depending on the species, plants may be evergreen or summer deciduous. White and shades of pink are the most common flower colours, except for L. cotyledon which exhibits lovely striped flowers in sunset shades. Some are relatively easy in cultivation while others are very difficult to grow in areas outside their natural range. Obviously, gardeners in western North America will probably have more success than those who live in the east. As a rule, they need exceptionably well-drained soil, especially around the neck of the crowns and shade from hot afternoon sun. Most success is found when growing then on north or northwest-facing slopes. Evergreen types prefer to have their crowns relatively dry in winter, hence planting on a slope is essential. In European botanical gardens, lewisia are primarily grown in alpine houses which provide the drier winter conditions and more careful attention to culture. In my own garden, I grow lewisia is clay pots and overwinter them plunged in a cold frame. Perhaps a lot of work, but well worth it as few alpines are as spectacular. I have purchased several from specialty alpine nurseries while others I have grown from seed. If going the seed route, stratify them for 8 weeks before sowing.
Lewisia adapt very well to pot culture
As mentioned, one of the most popular and among the easier species is L. cotyledon. This is an evergreen species with rosettes of elongate, wavy-edged, succulent leaves. The colour range is the greatest of any lewisia and is no doubt, the reason for its popularity. Many selections have been made over the years, some in solid colours but the most popular being striped. Colours range from pure white through yellow, orange, pink and red. They have a main flush of bloom in late spring but often produce scattered flowers all season. In the wild, they are found in northern California and southern Oregon, especially the Siskiyou Mountains.
Some of the rainbow colours exhibited by L. cotyledon
If growing in the open garden, nestle them between rocks facing north or northwest
Another relatively easy evergreen species is L. columbiana. This one has multiple rosettes of narrow, almost terete leaves. The flower stems are relatively tall and wiry, topped with a cloud of small, delicate white to pink flowers in late spring. It is native to Washington, Oregon, Idaho and southern British Columbia.
Lewisia columbiana and the rare white form
Perhaps the most spectacular of the evergreen types is L. tweedyi. This one has the largest flowers, in shades of soft peach or apicot. Flowers sit just above the relatively large, fleshy leaves. This species is more challenging than the previous two. It hails primarily from the Wenatchee Mountain range of Washington but extends into extreme southern British Columbia.
Pictured above are the two common colour forms of L. tweedyi
Lewisia longipetala is rarely seen in the garden, but hybrids between it and L. cotyledon are among the easiest lewisia to grow in the open garden. Plants produce rosettes of narrow succulent leaves and, for me, bloom all summer long. The most popular hybrids are ‘Pinkie' and ‘Little Plum'.
Popular hybrids are 'Little Plum' and 'Pinkie'
The other more common lewisia seen in gardens are herbaceous. The most spectacular, and unfortunately, the more challenging of these, is L. rediviva. This species sends up a small rosette of leaves in the fall or early winter which then remain dormant until the spring. At this time, several nearly stemless large pink or white flowers are produced. After flowering, the plants go dormant and disappear until next fall. While dormant, they need to be kept completely dry, then resume watering in late September. This is not easy to accomplish in the open garden, but pot culture makes this relatively simple. In nature, this species has the widest distributional range of any lewisia, being found in all the western States and southern British Columbia.
The other two lewisia I grow are L. pygmaea and L. nevadensis. Both species are found in a wide range of western United States. They will go dormant in the heat of the summer but do not require the bone-dry conditions of L. rediviva. This makes them among the easiest lewisia to grow in the open garden. In my cool summer area, they never go summer dormant and bloom all season, even self-seeding. The former species has prostrate stems ending in loose clusters of bright magenta-pink flowers. The latter has solitary, nearly stemless flowers which are typically white or mauve-pink in the form ‘Rosea'.
Pictured above are L. rediviva 'Alba', L. nevadensis, L. nevadensis 'Rosea' and L. pygmaea
The other species are all quite challenging in cultivation and not readily available. Certainly, I have never tried any of them, but all the above species I have grown with relative success as pot-grown plants (except for L. pygmaea and L. nevadensis which are in the open garden). If you like to grow plants in pot culture or are an alpine enthusiast looking for that slightly challenging plant, then Lewisia should be high on your list!