My inspiration for this column comes from beautiful clematis vines trailing over the walls of the Secret Garden at Thanksgiving Gardens. These beautiful flowers almost begged to be translated into words. This genus is a member of the buttercup family and has more than 250 species and numerous garden hybrids. The word clematis is from a Greek word meaning "vine."
This genus includes many different plants that are mostly woody, deciduous climbing vines. Most varieties are cold hardy to USDA zone 3, so they survive throughout Utah. Clematis show great variety in flower form, color, bloom season, foliage and plant height. The leaf stalks twine like tendrils and support the plants.
The flowers have three forms: small white flowers in loose, irregular spreading clusters; bell or urn-shaped flowers; and flat or open flowers. Some produce showy, ball-shaped or feathered fruits. Many species of clematis have fragrant blooms, but most hybrids do not.
The large-flowered hybrid blooms range from 4 to 10 inches in diameter and can produce as many as 100 blooms per plant each season. The blooms of other species types range from 1 1/2 to 3 inches in diameter and have many diverse shapes.
Clematis were insignificant nursery plants until breeders developed hybrids in the 1850s. Breeders crossed Oriental and European species in Europe until the 1890s. This was the "Golden Age of Clematis," and they introduced more new varieties than any other time in history.
Many popular varieties grown today originated then. Britain's leading hybridizer in the 1860s was the Jackman Nursery, and in 1862, the folks there introduced Clematis x jackmanii, which is still the most popular variety of clematis grown today. Although interest waned in hybrids, there is renewed interest in hardy and disease-resistant small-flowered clematis.
Some complain clematis are difficult, but they'll thrive if you select the right site and give them good care. Clematis prefer six hours of full sun but need some protection during the heat of the day. The plant's stems and foliage need sun, but keep the roots in a cool, moist environment. Some red and blue large-flowered hybrids and bicolor flowers fade badly if they get too much sun. Plant these on eastern exposures or in partial shade.
Perhaps the most serious problem for Utah gardeners is our soil. Clematis prefer rich, well-drained soil and a soil pH near neutral (7.0). If you have heavy clay, alkaline soil, amend it with organic matter to improve the drainage, and add iron chelates if your plants turn yellow.
The real mystery of growing clematis is learning how to prune the vines. Prune each year to maximize flowering. The plants will flower without pruning, but the flowers are usually not where you want them. The mystery comes because not all clematis are pruned the same.
There are three major groups, depending on the time of year the plants flower. The earliest flowering clematis need no new growth for plants to bloom, but the later flowering types must have new growth for flower buds to form. Some types may cross lines.
In addition, clematis vines can become entangled, so make cuts carefully, then spread and train the vines to cover the maximum possible area. This displays the blooms for their maximum effect.
The early-flowering clematis (usually called Group A) bloom in April and May from buds produced the previous year. Prune these after they bloom before the end of July. This allows new flower buds to grow for the next season. Remove shoots that bloomed previously and prune vines to reduce the size or make a good branch framework. Do not cut into the woody trunks. Plants in this group include C. alpina, C. macropetala, C. armandii, C. montana and C. chrysocoma.
Large-flowered hybrids (Group B) bloom in mid-June on short stems from the previous season's growth and often rebloom with smaller flowers in late summer on new growth. Remove dead and weak stems in February or March, and then cut back remaining stems to the topmost pair of large, plump green buds. This cut could be a few inches to a foot or two from the stem tips.
These plants often become bare at the base as they mature. Under plant them to help conceal the stems. You can often force a flush of new growth from the base by cutting the vine back to 18 inches immediately after the flush of bloom in June. Plants in this group include Nelly Moser, Miss Bateman, Lasurstern, Duchess of Edinburgh, Mrs. Cholmondeley and others.
Late-flowering clematis (Group C) flower on the last two to three feet of this season's growth. Some types begin blooming in mid-June and continue into fall. This group is easiest to prune since you do not need to maintain old growth. Cut each stem two to three feet long in February or March. This removes some good stems and buds, but the plant still blooms well.
Eventually the length of the bare stem at the base will increase as the vine matures. Plants in this group include C. viticella, C. flammula, C. tangutica, C. x jackmanii, C. maximowicziana, Perle d'Azur, Royal Velours, Duchess of Albany and others.
Look for many favorite clematis at local nurseries right now. Some native species thrive in our area and even flourish as low water-use plants. Make this season the one to add some of these beautiful plants to your garden.
Larry A. Sagers is the regional horticulturist, Utah State University Extension, at Thanksgiving Point.