Lewisia, named after explorer and botanist Meriwether Lewis, form a group of Western alpine perennials containing about 19 species. These species readily hybridize in the wild, forming stronger plants. They are usually sold in 4-inch to gallon pots with gorgeous flowers that can vary from striped pastels to gem-like tones of magenta, red and orange.
These are typically sold in late spring to early summer and are grown from color mixes. The caveat is that the plants do not rebloom as they go to seed, and it’s hard to sell a plant out of bloom. The breeders at Terra Nova Nurseries, however, have begun a new series – named “Constant” – that bloom and then reflush with flowers three to four times.
By careful crossing, the staff has created sterile forms that expend energy on more flowers and less on producing seed. Some of the species are sensitive to too much sun and need minerally, “rock garden soil.” These plants are stronger and tolerate a wider range of soils and climactic conditions. They’re graceful, rosetted-plants that are tolerant of full sun to shade and are ideally placed in a Northern location with a cool root run.
As there are a good number of species to choose from, the Terra Nova team was able to cross the most vigorous species including Lewisia cotyledon, L. rediviva, L. columbiana, and L. tweedyi.
Producing sterile hybrids, however, is the rub. Typically hundreds of crosses are grown and evaluated for fertility and length of bloom-time. Once the “winners” are selected over the course of years, they are put into tissue culture to produce any number of plants that are needed. This multi-year evaluation covers the vagaries of different winters and summers and plant survival. Samples are commonly sent to nurseries that are Terra Nova licensees around the world for testing.
While it would be possible to divide these plants, their propagation is not possible by making URCs – unrooted cuttings. No seed is produced, so it’s one of those plants that must be made by tissue culture techniques, which will also ensure stability in the end product. Tissue cultured plants are usually offered in stage III, which are rooted plants in agar (usually 25 plants per container). These will need to be weaned in high-humidity tents after transplanting to soil. Plugs are available as well, being plants in soil, typically 72 plants per flat. These are grown out in the greenhouse until they can be shipped and transplanted to a larger pot by the grower.
Producing and growing Lewisia
Lewisia are alpine plants with succulent leaves. Just the word “alpine” implies that they are cooler growing plants like Hellebore and Pulmonaria, so they would prefer to be grown on the ground where root growing temperatures are typically 15 degrees cooler than those grown on benches.
Being an alpine also implies the need for sharp drainage. Although the Constant™ Series can tolerate a heavier mix, heavy clay soils or wet-peaty soils are generally avoided. Typically a well-draining mix with bark with a pH range of 5.5 to 6 does quite well. Alpine plants need low rates of fertility. EC (electrical conductivity) rates of a balanced feed at .6 to 1 are a good level at which to grow the plants. This is not a plant where one fertilizer fits all. Most annual liquid-feed levels are too hot and will burn emerging roots.
Drying out between waterings is also helpful to grow better roots. Mind you, these are very hardy, tough plants, and paying attention to this growing framework produces great impulse items. As far as light is concerned, start with moderate levels after transplanting and bring it up (remove shading) as the root system develops in a few weeks.
Plants can be moved outdoors once acclimatized to the light. Finish times are usually six to eight weeks from 72-plug to a 4-inch container. Of course, time must be added for those who bring in the Stage III plantlets in agar. If you are looking to grow in gallon pots, allow 12 weeks of grow time. As the plants are rosette-growing, they will produce huge amounts of flowers from many rosettes on a second-year plant. Growers should aim for having budded plants on the retail nursery floor in April, as they will bloom and rebloom all the way into June.
Mature plants of Lewisia have multiple crowns of rosettes that form a low mound in two years’ time. Plants that come to the nursery from Terra Nova will have a single crown that will bloom in the first season. In our test plots in our fields, the Lewisia Constant™ Coral plants had as many as 40 rosettes in a low, 8-inch mound.
Terra Nova’s Lewisia collection
Lewisia CONSTANT™ ‘Coral’ has a profusion of coral flowers edged lightly in white. Soft, succulent leaves are arranged in a rosette fashion, which multiply from the base as the plant ages. Selected from hundreds of other seedlings, this sterile hybrid continues to flush (in Oregon) into early fall. Four-inch-tall foliage will spread to about 10 inches the first year. The spikes of flowers grow to only 8 inches tall. Hardy to USDA Zone 4. This plant does well in containers with good drainage and in the landscape in the front of the border or under ornamental shrubs, helping to extend their blooming season.
Lewisia CONSTANT™ ‘Fuchsia’ has the densest inflorescences of the entire Constant ™ series. Selected as the best fuchsia- flowered form from hundreds of other seedlings, this sterile hybrid continues to flush (in Oregon) into early fall. Four-inchtall foliage will spread to about 10 inches the first year. The spikes of flowers grow to only 8 inches tall. Hardy to USDA Zone 4. This plant does well in containers with good drainage and in the landscape in the front of the border or under ornamental shrubs, helping to extend their blooming season. It is also a delight planted en masse along gravel pathways to make the transition to flower beds.
Lewisia CONSTANT™ ‘Comment’ was Terra Nova Nurseries’ first introduction in the CONSTANT™ series. Visitors were struck by the brilliant, magenta-tinted bloom, especially summer visitors who were not used to seeing Lewisia in bloom at that time of year. The 4-inch-tall foliage will spread to about 10 inches the first year. Ensuing years show a plant that does not fall apart and simply gets better! The spikes of flowers grow to only 8 inches tall. Hardy to USDA Zone 4. This plant does well in containers with good drainage and in the landscape in the front of the border or under ornamental shrubs, helping to extend their blooming season.
Ornamental traits and landscape applications
Lewisia are plants that look fantastic when placed near a stone, or as a mass along gravel pathways in the garden. They can tolerate shade and drought, which would qualify them as an understory plant in the garden. Planted under a Rhododendron, they will tolerate the competition for moisture and extend the “flash in the pan” color from the rhodies into late summer. They are effective in clustered sets of pots, providing enough color and attractive form to draw the eye away from plants in the larger pots.
These long-lasting flowers are also attractive when planted in terra cotta pots as a gift plant. The tight rosettes are small enough to qualify their use in a miniature garden. Most gardens have problematic parts with poor soils or gravelly areas. Lewisia can take to these spots with aplomb.
Maintenance is minimal, with expired flower heads that can be sheared off by the fastidious gardener, or just left alone as the new growth and rebloom comes through the old flower stems. Pest problems outdoors are minimal. In the greenhouse, mealy bugs should be monitored and Botrytis can attack if the foliage is kept too wet. As these plants are not bullies, one must use care in selecting their pot-mates. They can be combined with dwarf Heuchera for striking effect.
An upright plant, like a dwarf Juncus, can make a cool combo. While rock gardens are just emerging on the American scene, these plants make an excellent addition, providing much more show than the seed-grown forms. Troughs are becoming more popular and are often filled with a low-fertility, high mineral soil that lewisias relish. Thinking outside the box, these lewisias could be used, mixed in a rooftop garden, where color is often needed.
Green walls may be too moist, but could certainly be tried with these more-moisture-tolerant plants. Their compact nature, range of colors and low maintenance might make them perfect! Lewisia have been seen planted in multiple smaller and lower pots ascending a stairway, the thick taproot allows waterings to be missed. These plants are extremely hardy; in fact, one variety is Montana’s state flower, commonly called bitterroot. It was used medicinally and as a food source for the Flathead Indians.
While the USDA Hardiness Zone is listed as 3 to 8, it is felt that a range of 4 to 8 might be a safer guideline as different species of lewisia. Very high heat and humidity are problematic in some areas of the United States where planting in a north exposure with the coolest root run possible might give this plant a chance.
Lewisia are known by the industry as a hot impulse item. Terra Nova Nurseries has improved this plant to put on additional flushes of flowers, extending the sales window greatly, and making it a better plant for consumers and growers alike.