Home » Plants » Clematis terniflora

Sweet Autumn Clematis (Clematis terniflora DC.)

Also known as sweet autumn virginsbower, sweet autumn virgin's bower; also classified as Clematis paniculata Thunb.

The name Clematis paniculata Thunb. refers to Clematis terniflora var. terniflora, the only variety of this species found in North America. This is unrelated to Clematis paniculata J.F.Gmel, which refers to a species native to New Zealand and not found in North America. Unfortunately, most gardening websites are sloppy and do not note binomial naming authorities, and worse, the horticultural community often continues using incorrect names decades or even centuries after corrections have propagated through the scientific community. It is thus common for gardening sources to refer incorrectly to this taxon as Clematis paniculata, which has led to some confusion and misinformation, such as sources that refer to the New Zealand species being invasive in North America, which is not the case.

Page contents

Range
Habitat
Life Cycle
Control
Uses
Links
Photos

Photo © Nathan Aaron, CC BY 4.0.

↑Range - Expand

Legend	Color
Introduced
Introduced or Not Present

This tentative map is based on our own research. It may have limited data on Canada and/or Mexico, and there is some subjectivity in our assignment of plants as introduced vs. expanded. Read more in this blog post.

Although this plant occurs somewhere in each of these regions, it may only occur in a small part of some or all of them.

↑Habitat

Clematis terniflora is primarily found in disturbed edge habitats where it mostly occupies a zone of about 20 feet in height or lower. Although it can occur in natural forest edges and early-successional habitats following disturbance, it is more common in anthropogenic habitats, such as edges between forests and mowed fields, minimally-maintained thickets, fence rows (particularly along chain link or other open fences), partly-wooded waste ground, and areas where roads or railroads cut through wooded areas. It relies on soil disturbance to establish and does best on sites where there is little competition from ground-level flora, and some structure (whether from trees or shrubs or human-made structures) to climb.

Plants will grow in full sun to light shade. Plants are most aggressive in loamy to clay-loam soil textures, but can also tolerate gravely or sandy soils. This species has an advantage where soil fertility, moisture availability, and drainage is patchy, as it can root in an ideal spot and then climb to cover plants in areas with less-ideal soil conditions.

We could not find a source on this plant's pH preferences in the wild, but it likely is absent from the most acidic soils and prefers soils closer to neutral. Gardening sources describe its pH range as 5.5 to 7.5 with some saying it needs a minimum of 6.0.

It is not known how much the occurrence of this species primarily in anthropogenic habitats is a function of its innate preferences, vs. its history of introduction from garden escapes, combined with the fact that humans often still encourage or at least tolerate this species in managed landscapes. There may be a combination of both factors. It definitely benefits from management practices that disturb the ground and allow it to seed into an area along an edge, where it can then climb branches of existing vegetation, and it also benefits from fences and other structures it can readily climb.

↑Life Cycle

Seedlings germinate in exposed ground and quickly grow a deep taproot, which develops into a fibrous root system from a node usually quite deep beneath the ground's surface, usually at least several inches and in loose soil sometimes as deep as a foot. The primary growth form of this plant is to send out long, thin shoots which have compound leaves with long petioles; the leaflets and petioles wrap around objects and function like tendrils, even though this vine lacks true tendrils. The leaves, twig, or other long and narrow objects, in order to support the plant. Unused leaves are rapidly shed, leaving long, bare stems in places. With time these stems acquire a

The root system is highly aggressive and competitive within a small area, excluding other plants from rooting nearby, but often does not spread much horizontally. This rooting habit is likely why this plant thrives in areas of patchy soil fertility.

Established plants send up multiple shoots, which can at least temporarily support their own weight reaching to a few feet in height while searching for structure to climb. Stems can sometimes lean against a flatter vertical surface such as a tree trunk or fence long enough to climb it to a height of 6 feet or more, until they reach a material that they can more easily attach to.

Because this plant grows rapidly, once it is established near the growing tips of a tree or shrub, it can usually grow faster than the supporting plant and smother it. It is particularly likely to out-compete supporting vegetation when it is rooted in an area of higher soil fertility, drainage, or moisture availability, which can occur both when the vine grows onto a drier upper slope, or grows out over an open wetland.

Although technically classified as a woody vine because it has perennial aboveground growth, this species invests much less energy in the structure of its aboveground stems than is typical for woody vines. This scenario results in a tradeoff: it grows faster than most woody vines, but its stems are weak, it is less likely to remain upright if its supports are removed or damaged, and it cannot reach the canopy of tall trees. It also stores relatively more energy in its root system, which makes it more resilient to top-kill. The lifespan of individual stems is often much shorter than the lifespan of the plant as a whole. Individual stems can be killed by being cut or physically separated, by herbivory, or can die slowly if they get shaded out. In response to top-kill, a vigorous plant will resprout and send up new shoots in search of light and structure.

Plants are capable of vegetative reproduction, through shoots that come into contact with soil growing new root systems at nodes, but this species reproduces vegetatively much less than a number of other woody vines. Most reproduction is by seed.

Established plants flower in late summer into early fall, with seed maturing shortly thereafter. Seed is wind-dispersed, and germinates in the next spring, following a period of cold dormancy. We have not seen any evidence or records of this species forming a persistent seed bank, but it is also hard to establish that it does not form a seed bank as this species is so abundant where it occurs, and its seeds can travel long distances in the wind, so when a seedling arises, it is hard to verify that it did not occur from a wind-blown seed from the most recent year's crop.

Foliage is opportunistically semi-evergreen, being more likely to retain its foliage through the winter in warm winters, in the south of its range, and on more sheltered sites.

We could not find much information on the lifespan of this plant in the wild, but it is common for garden plants to have a root system that persists for 10 years or longer. Individual shoots often only live 2-5 years. Plants on well-drained, undisturbed sites are most likely to be killed slowly by shade as a forest canopy closes above them, as this plant cannot climb high enough to reach the canopy of a mature forest. On wet sites, plants can be killed by prolonged flooding. Herbivory, drought, or sporadic mowing usually only top-kills plants.

↑Control

This plant is difficult to control because it is so common in gardens and often recolonizes a site following removal. It is also highly resilient to top-kill, to the point that only trimming above-ground parts of the plant will only slightly slow its growth in the short-term, and do nothing in the long-run.

Individual plants can be killed relatively by digging up the node with a shovel. Small pieces of root will not resprout; if the made node is dug out, the plant will die. Because this plant roots deeper than most vines, care must be taken to dig deep enough to dig out the fibrous root system around and below the node; breaking off the stem above the node will result only in top-kill and resprouting. Often, even small-looking plants require a shovel, not just a hand-trowel, because of the depth of the root system.

This plant has some susceptibility to herbicide; it has been found susceptible to fluroxypyr, glyphosate, imazapic, metsulfuron, and triclopyr, in the sense that it will be greatly reduced in extent after herbicide application. However, unlike digging, herbicide often does not fully kill the plant on the first application. Furthermore, herbicide can often cause damage to non-target vegetation, and this species is usually found smothering other vegetation that will be harmed by the herbicide. A more targeted approach can be carried out by cutting stems to the ground, and then spraying only the resprouts, thus targeting a weakened plant and minimizing damage to non-target vegetation. However, because of this plant's resilience in resprouting, and the ease and effectiveness of digging out the root system, we have seen scant evidence that herbicide is a labor-intensive and cost-effective method to control this plant.

The most difficult aspect of controlling this plant is preventing recolonization. To this end, removing source populations and coordinating efforts so that all land owners and/or managers remove this plant together, is often necessary to fully remove it from an area. Where removing all source populations is not possible, recolonization can be reduced by establishing dense ground-level herbaceous vegetation and/or by allowing tall trees to grow up in an area and develop a closed canopy.

Examining and changing management practices is often necessary to prevent reestablishment. Fencerow management can favor this plant by weedwhacking or applying herbicide at the base of a fence, thus giving this plant space to establish where it will have an immediate structure to climb. Allowing dense herbaceous growth to cover the ground at the base of fences can prevent this scenario. Similarly, the pruning of low branches from trees on a forest edge can increase light penetration into an area near the edge but far enough back for this plant to root, which can facilitate its colonizing the edge. Similarly, periodic weedwhacking or bushwhacking of edge vegetation (especially at intervals of 2-5 years, close to the lifespan of this species' individual stems) can favor its establishment along edges. A combination of refraining from pruning low branches along edges, and seeding dense herbaceous vegetation along the edge and allowing it grow without mowing, taking care to mow or trim the edge at a consistent location each year, can prevent this plant from establishing.

↑Uses

Clematis terniflora has been widely planted in North America as a garden plant, where it is valued for being easy to grow, and its pleasantly-fragrant blooms. However, it can be aggressive both in a garden setting in the wild, and it is now widely-agreed-on to be an invasive species, and is illegal to sell in many states.

We recommend against planting this species for any reason anywhere in North America because of its invasive status. Furthermore we recommend removing it anywhere it occurs in gardens as it tends to seed out into wild areas.