by Marilyn Loser
2020 August 12
Late last fall friends requested I do a column on Chinese clematis (Clematis orientalis) as they had a tree in their yard killed by this pest. It took years, but the nasty vine did kill the tree. I was amazed as I had never heard of this particular species of clematis. The genus clematis includes more than 200 species with many hybrids. So, many clematis are just wonderful.
One place you can see Chinese clematis growing in Alamosa is along the south side of the Rio Grande east of State Avenue between the path and the river near the river bend. It’s not hard to identify at that spot, especially when its yellow blooms adorn the plants from August to September or the feathery seed heads hang on over the winter.
According to the Colorado State University agriculture weed website (www.colorado.gov/ag/weeds), it is an “herbaceous to woody vined perennial that is native to Eurasia. It is an escaped ornamental species that is a deciduous climber growing up to 12 feet.” However, some of the plants along the river are much taller than this. Also, some sites say it can only go as low as cold hardiness zone 4. We often have zone 3 winter lows (between -30 –to -40 degrees F) and it seems to be doing fine here.
Its solitary flowers have four yellow sepals (petal-like structures) that are often nodding. Each flower produces numerous feathery, long-tailed fruits which are conspicuous all winter.
According to the website, “Chinese clematis can cause death to young trees and brush. It out competes native shrubs and herbaceous species. Plants will completely cover rock walls, trees, bushes and fences. The juice of freshly crushed leaves and stems have blister causing agents.” Be careful when handling it.
Native to Asia and central Europe, it was originally planted in the United States as an ornamental but escaped cultivation and naturalized especially in the western states of Colorado, Nevada, Idaho, Utah, New Mexico, and Oregon.
I have some Colorado native clematis (Clematis ligusticifolia) that I’ve always called virgin’s bower. Fortunately, it has white flowers. The feathery, long-tailed seed heads which I love to see in the winter have seed clusters of 3 ping-pong ball sized heads as opposed to the Chinese variety with golf-ball sized heads with just one cluster.
There are other varieties of yellow clematis that are safe – they tend to have larger flowers and darker blooms. I’ve decided I will avoid any yellow clematis! At one point I had a yellow species, “Clematis tangutica” that I bought at a nursery. It has since died out and I won’t replace it. I’ll stick with my showy pink and white clematis (Clematis hybrid "Dr. Ruppel") and purple ones (Clematis x jackmanii).
The best way to control Chinese clematis is to prevent the plants from going to seed. Pull the woody stem prior to flowering, if you can identify it, and certainly before they go to seed. You can also dig when soil is moist. Make certain to remove all the roots. If flowering, bag specimens carefully so as to not scatter seeds. Even if they are flowering, if you toss them in the yard recycling in Alamosa, they could develop seed heads and spread later in distributed recycled mulch.
Chinese clematis is on the Colorado B weed list which means it is required to “be either eradicated, contained, or suppressed depending on the local infestations,” according to the CSU weed website. I haven’t seen anything locally about having to eradicate it.
Happy gardening and I hope we don’t have a frost too early!
From a sign on a tree photo at Alamosa’s North River Greenhouse Facebook page. “Advice from a tree. Stand tall and proud, go out on a limb, remember your roots, drink plenty of water, be content with your natural beauty, enjoy the view.”