Gardening Columns

Beautiful Plants or Troublesome Invasives?

First published on garden.org on September 11, 2008, by Suzanne DeJohn

OK, I'll admit it. I've knowingly planted invasive species. Well, sort of. Our fence is draped with white sweet autumn clematis, 'Heavenly Blue' morning glories, and red cardinal climber, all of which could be considered invasive in our region. (Does the patriotic color scheme offset the offense?) But I must say that the combination is beautiful.

Sweet autumn clematis (Clematis terniflora) is native to Japan and China and is on invasive plants lists for Alabama, Georgia, South Carolina, and Tennessee. With North Carolina bordering three of those states, it's a fair bet that the plant can pose problems here, too. Had I known about the similar but native C. virginiana, I would have opted for that. But my plant was an impulse buy. I plead ignorance.

Morning glory (Ipomoea tricolor) is listed as a noxious weed in Arkansas and has the reputation for being an abundant self-seeder. Cardinal climber (Ipomoea x multifida) isn't on any invasive plant lists yet, but one of its parents, cypress vine, is on the invasive species list for the North Carolina Native Plant Society, albeit listed as a "lesser threat." I can't help myself, I plant morning glories every year -- I just love the color of 'Heavenly Blue'. Our farm field is filled with bindweed, which I mistakenly thought was a related plant, but it's in a different genus, Convolvulus. The flowers are so similar it's hard to believe they're not related.

I'm not too worried; these plants probably aren't going to take over anytime soon. But they're a good reminder that we should be vigilant in our plant purchases. Many invasive species are still readily available at garden centers. After all, an invasive species is usually hardy, adaptable, and easy to grow, all qualities we look for in landscape plants.

Plant Prohibition
Just this summer, the North Carolina Department of Agriculture prohibited the propagation, sale, and distribution of cogongrass (lmperata cylindrica), including the popular 'Red Baron', also called Japanese blood grass. Georgia banned it in May. Considered more of a problem in the south because it seeds more readily in warm climates, the plant is nonethless banned as far north as Minnesota. An international group of botanists has dubbed cogongrass "the seventh worst weed in the world," yet it's still being sold. A cursory Web search yields several suppliers. The online companies must be aware of the plant's invasive nature since they list the states to which they can't ship it, but they sell it anyway.

I don't have cogongrass, but I planted an attractive striped ornamental grass that's slowly taking over a garden. It has finally reached the bee balm; I'll be curious to see which one wins out. It's like watching a prize fight in slo-mo. (Although bee balm is native, this mint relative is a vigorous spreader and could certainly be described as invasive.)

Unfortunately, many gardeners buy on impulse. We walk by a plant and if we like it, we just have to buy it. Then we get it home, plant it, and some time down the road find out its bad habits. I suppose when we all have Internet access on our cell phones we'll be able to search invasive plant lists as we shop, but for now we just have to acquaint ourselves with the worst offenders -- especially those most likely to be available in stores and online. To that end, here's a short list of plants on invasive plants lists for our region that are still readily available for purchase:

Bugleweed (Ajuga reptans)
Five-leaf akebia, also known as chocolate vine (Akebia quinata)
Silk tree, also known as mimosa (Albizia julibrissin)
Porcelainberry (Ampelopsis brevipedunculata)
Mugwort, also known as common wormwood (Artemisia vulgaris)
Japanese Barberry (Berberis thunbergii)
Butterfly bush (Buddleja davidii)
Russian olive (Elaeagnus angustifolia)
Burning bush (Euonymus alatus)
Wintercreeper (Euonymus fortuneia)
English ivy (Hedera helix)
Lantana (Lantana camara)
Privet (Ligustrum spp.)
Chinese silver grass (Miscanthus sinensis)
Japanese spurge, pachysandra (Pachysandra terminalis)
Princess tree, also known as royal empress, royal paulownia, or empress tree (Paulownia tomentosa)
Japanese spirea (Spiraea japonica)
Periwinkle (Vinca minor)
Chinese and Japanese wisterias (Wisteria floribunda and W. sinensis)

For more information visit: http://www.invasive.org/weeds.cfm.

It's easy to dismiss the potential for trouble with plants like these. But much of our property is overrun with privet, Japanese honeysuckle, English ivy, mugwort, periwinkle, and multiflora rose, to the exclusion of most other plants. Nearby, infestations of kudzu and bittersweet have taken their toll. All of these plants were introduced to this country as ornamentals, and they're thriving despite this summer's prolonged drought. Hardy, adaptable, easy to grow ... and invasive.