Sweet autumn clematis, Clematis terniflora is a vigorous woody vine in the buttercup family (Ranunculaceae) native to Japan sometimes sold as C. maximowicziana, C. paniculata and C. dioscoreifolia (however, C. paniculata is really a different fall-blooming species native to New Zealand). This deciduous perennial that is hardy in zones 4-9 was introduced in 1877 as seeds sent to the Arnold Arboretum in Boston. Blooming in the fall, it often goes unnoticed until it blooms. Because C. terniflora aggressively self-seeds and has escaped cultivation in many parts of the U.S. is to invade forest edges, right-of-ways and areas along streams and roads, it is often considered an invasive species – particularly in the East and Midwest – and is no longer recommended as a landscape plant in many states. In Wisconsin it is not a regulated invasive plant on the DNR NR-40 list, but still should be used with caution. Before planting check to be sure that sweet autumn clematis is not invasive where you live.
The similar-looking, but not very fragrant, Virgin’s-bower, C. virginiana, native to eastern North America blooms about the same time, and could be used instead, but is not as readily available in the horticulture trade. It is normally dioecious (separate male and female plants) so a single plant will not produce seed, but it, too, will produce plenty of seed where there are multiple plants and reseeds readily. Both the exotic and native vines can be sold under the same common name, sweet autumn clematis, so examine the leaves to determine which plant you are really purchasing. The leaf edges of C. virginiana are serrated or toothed while those of C. terniflora are mostly entire (smooth).
The foliage of C. virginiana tends to be lighter and its flowers are hairy on the underside and bloom later, but those characteristics may not be useful when purchasing a plant in a container. Climbing hydrangea, Hydrangea anomala subsp. petiolaris,is another possible substitute, with faintly fragrant flowers (some suggest the scent is unpleasant) blooming earlier in the season.
C. terniflora can grow up to 30 feet long, overwhelming everything in its path. The shallowly-grooved stems grow from a tap root, starting out green and developing light brown, longitudinally shredded bark on mature stems. The opposite leaves are a shiny green, with each leathery, pinnately compound leaf having 3-5 oval to elliptic leaflets. The apically round and basally cordate leaflets can be toothed on young plants but are entire when mature. The tendrilous leaf petioles on this twining vine twist around, helping it climb on structures or woody plants.
As the common name suggests, this plant blooms in late summer or fall. By mid-summer tiny buds begin to show and in the upper Midwest start to open typically in August and September. Although the individual star-shaped flowers are only about an inch across, the plant is very florific, with the flowers nearly completely covering the foliage so it is very showy. The numerous fragrant flowers are produced in terminal branching panicles of 3-12 flowers. Each monoecious flower has four pure white, narrow, petal-like sepals, approximately 50 stamens, and 5-10 pistils with long, plumose styles. The flowers are attractive to insects, especially bees and flies.
The flowers are followed by silvery plume-like seed heads typical of the genus (the dry fruits are a flattened achene each with a silky-plumose tail) which are dispersed by wind. The mass of fluffy seed heads can be quite ornamental. This plant can self-seed prolifically and the wind can blow the seeds great distances to potentially invade natural areas, so is considered invasive in many places. In colder climates (zones 4 and 5) it does not produce as many volunteers as in warmer locations. To prevent any seeding, cut the entire plant back to about three feet as soon as the flowers fade.
Plant sweet autumn clematis where it can climb up a structure – such as a fence or pergola – or ramble over an open area as a ground cover. It is far too rambunctious for a normal trellis. With its dense foliage and rampant growth habit it can quickly cover a chain link fence, arbor, or other structure to create a seasonal screen or cover eyesores such as old stumps or obscure an unsightly building or wall. Without support it forms a dense tangle of vines that will choke out other vegetation. Although it could be allowed to grow through large shrubs care would have to be taken to make sure it’s abundant growth doesn’t completely cover the other plant. Because of its pleasant vanilla-like sweet fragrance, try to situate it where the scented flowers can be appreciated.
Grow sweet autumn clematis in full sun to part shade in well-drained soil. Although it tolerates shade, it will bloom better in full sun. This species blooms on new growth, so it can be pruned hard in fall after flowering or in early spring to keep its rampant growth somewhat in check. Each stem can be cut back to a few strong buds a foot or two off the ground in late winter or early spring. Like all clematis, it likes “cool feet,” so the soil at its base should be mulched or shaded other plants. Fertilize in spring with a low-nitrogen fertilizer and keep evenly moist throughout the growing season. This plant has few insect or disease problems and is not favored by deer. This vine is not affected by juglone, so can be grown near black walnut trees. It is readily propagated from seed sown outdoors in the fall, softwood cuttings taken in spring, or semi-ripe cuttings taken in early summer. It may-grown take up to five years before seed-grown plants bloom.
– Susan Mahr, University of Wisconsin – Madison
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