September Anti-Perennial of the Month-Sweet Autumn Clematis

My heart skipped a beat the first time I saw sweet autumn clematis, Clematis terniflora, scrambling up a trellis in full bloom. I promptly purchased the vine and planted it on my gate arbor, where it made my heart sing come late summer through fall with its billowy blooms. My other horticulture friends warned me about it reseeding everywhere, but I hadn’t noticed any stray volunteer seedlings anywhere for years.

 Until I did.

I saw it in my backyard, in the front yard. In the neighbor’s yard. Down the street, along the highways, covering fences, other shrubs, and even buildings. The trick it uses is to remain green and basically camouflaged throughout the growing season while it slithers and snakes up unsuspecting shrubs and structures, then BAM, out of the blue, it seems like it’s in full bloom overnight, and is suddenly EVERYWHERE.

I know, I know, oh, so pretty as it covers its invasive co-hort, Japanese honeysuckle, and abandoned or derelict landscapes. But there is hope. In fact, not all masses of white blooms every autumn is the invasive C. terniflora. The native, Clematis virginiana, sometimes called virgin’s bower, can also be vigorous, but not invasive. The two plants look very similar in bloom, with bright white, dainty flowers that show from late summer through October. The native is smaller overall with thinner leaves that have three leaflets with jagged edges, similar to a poison ivy leaf. Invasive C. terniflora’s three leaflets are thicker and entire with smooth edges.

Nurseries have mixed up these two species for years, so don’t always believe the tags. Check the leaves!

The two have similar cultural requirements, preferring full sun to part shade. Both suffer from the dreaded fatal fungus disease, Clematis wilt, along with issues from powdery mildew and other assorted pests like aphids and spider mites.

Getting rid of a patch of invasive sweet autumn clematis is best done in the fall by the “cut and paint” method of cutting the main stem down to ground level and carefully painting the stump with an herbicide. Attempts to broadcast-spray a large mass is wasteful, harmful to the environment, and gives poor results. A safer method is to dig out the plant, roots and all, then dispose of it in the trash, not the compost.

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Words and photos by Jo Batzer

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