When we first think about invasive plants, we often conjure images of plants that are not pretty. I often think of the brambles that Maleficent casts around the castle in Sleeping Beauty. Sharp thorns, jagged edges, overall, a barren landscape. Invasive plants are not new. We know that some thistles, leafy spurge, and palmer amaranth can render fields useless and unproductive. We have seen the damage that can be done to entire regions by kudzu. What was once an invited tree into the landscape, Bradford pear, has escaped cultivation and has started to become troublesome. What is considered invasive is not always defined as noxious. There is clear language that separates the two. A plant that is noxious is said to be harmful to the environment or animals. A plant that that is injurious to agricultural or horticultural crops[1]. An invasive plant is non-native to the ecosystem and who’s introduction will likely cause harm[2]. All Federally noxious weeds are invasive but not all invasive plants are declared noxious. After all, white clover, and dandelion, which are invasive, are openly welcomed plants into a growing number of lawns. However, what about the invisible invasive plants? The plants that go unnoticed and often welcomed into the landscape.
With flowers white as snow masked in a vanilla sweet cotton-candy fragrance; surely sweet autumn clematis can’t be an unwelcome visitor to our garden. However, state after state from Florida to New Jersey and Minnesota to Vermont is marking this late summer blooming vine is being as invasive. Sweet autumn will thrive in a wide range of growing conditions. Much like their showier cousins it performs well in full sun. However, unlike most other clematis, sweet autumn will perform well in partial shade making this a much sought after perennial vine. Just like the brambles around the castle, plants sold as sweet autumn do have a darker – sinister side.
Currently, there are two clematis species that are both sold as sweet autumn: Clematis terniflora and C. paniculata (syn. C. maximowicziana, & C. dioscoreifolia). Both species are winter hardy in Nebraska. C. terniflora is native to Japan and South China[3]. C. paniculata is native to New Zealand[4]. Both species of clematis can aggressively self-seed and pop up in undesired locations. Between the two species C. terniflora tends to be the more aggressive of the two and is known to smother saplings and kill mature trees. However, due to both plants often being used interchangeably in the landscape and marketplace makes it difficult and confusing to identify for those who are not familiar with the plants. Ideally it would be best to consider alternatives to either vine if you encounter them at your favorite garden center.
It is difficult to accept that plants that we often welcome into the landscape are not good neighbors. If you have sweet autumn in your landscape, make sure that you are cultivating out any volunteers to help reduce unwanted spreading into our natural areas. An alternative to the sweet autumn would be the woodbine (C. virginiana). This native perennial vine blooms in the fall.
[1] https://en.wikipedia.org/wiki/Noxious_weed
[2] https://www.invasivespeciesinfo.gov/what-are-invasive-species
[3] https://plants.ces.ncsu.edu/plants/clematis-terniflora/
[4] https://plants.ces.ncsu.edu/plants/clematis-paniculata/
