Invasive Species

Wintertime, the down time for a vegetable farmer without a greenhouse, finds me in the forest repairing barbed-wire fences. While there, I meander off with my trusty loppers and cut poison ivy vines at the base of the trees they are snaking up. The revelation that this obnoxious plant did not thrive as a woodland plant unless its leaves have access to sunshine surprised me. I happily relieve our forests of this rash-producing pest by simply snipping it off at ground level while taking a walk in the woods. After a few years, the small resprouting vines climbing back up need clipping, but gradually the persistent human will prevail. 

Most of the plant pests I eradicate are non-native invasive species. Without the natural checks and balances found in native habitat, these plants crowd out the local ones. Most of them were introduced as exotic specimens that escaped cultivation a long time ago. Although they can be pretty, there are pretty good reasons to get rid of them. We have plenty of beautiful natives that are compromised by aggressive foreign intervention. 

Nashville has many examples of forests so dense with privet and bush honeysuckle you can’t walk through them. I pull these shallow-rooted plants up when small and dig them up if they break off at the root. The creeping euonymus that threatens to smother the biggest of trees can also just be snipped off at the base, and the sprouts re-cut.

I dig the fragrance of wild roses, for a few weeks, but spend way more time digging them out of fence rows and pastures. The lovely, long arching branches love my ears, and frequently steal my hat.  A few whacks with the with the grubbing hoe helps loosen and remove them. Since the roots of plants die back proportionately to the amount cut, they are easier to pull or dig a few years later.

Kudzu concerns many who travel through the south and see it totally engulfing tall trees. It concerned me until a neighbor fenced off an acre of it and ran cattle on it. They relished this deep-rooted, soil-building legume for its protein-rich leaves, and its ability to bring up subsoil minerals that normal pasture plants can’t reach. There is not a trace of kudzu anywhere.

Three oriental, ornamental trees, although interesting, can become problematic. Tree of Heaven grows and spreads rapidly from both the winged seeds and the creeping yellow roots. Their tall, sparsely branched and worthless trunks tend to take over wherever they get started. Paulownia’s heart-shaped leaves are humungous on the saplings, and purples fragrant flowers adorn it in spring. The light-weight wood became very expensive for a short period 40 years ago. It was being shipped to Japan for carving trinkets and for shoe soles. A non-spreading clone of it is now available for growing wood to use for making guitars. Mimosa reminds me of a Dr. Seuss drawing, with its feathery foliage and cute, pink blossoms. These three water-loving trees grow fast, spread quickly, and once established are much harder to remove because of the deep roots.

The next five, non-native invasive species were brought to our farm from someone who should have known better, namely me. As a teenager I helped my dad plant Autumn Olive, a nitrogen-fixing, erosion-controlling bush, along the drainage ditches on his farm. So, I planted a beautiful hedge; the flowers smelled like jasmine and the berries were fun to eat. Ten years later I noticed it popping up elsewhere, from birds, I suppose. The Tennessee Army Corps of Engineers planted it along the Cumberland River so I’m not the only culprit. I’m oaky with Autumn Olive bushes improving soil and feeding wildlife on otherwise unused land, a bush hog can take care of them when need be. 

My friend, Adam, had a bamboo nursery and offered me a few starts. I transplanted five different species and they spread rapidly when unchecked. Its handy for building projects and erosion control but can become a real nuisance. The stalks of the biggest get four inches in diameter, but they die back to the ground if the temperature dips into single digits. 

In late winter you’ll notice wild pears blooming in abandoned fields and fence rows. Callery pears are the offspring of the popular Bradford pears crossed with another pear variety. This thorny invasive is very difficult to remove once they become established. Cut down every tree that you see, well, maybe not the ones along your neighbor’s driveway. I brought them here for grafting pear trees, but if the graft fails this rootstock can become trouble. 

A gardening neighbor planted the orange-berried Bittersweet, a vine her friend wanted her to grow to make wreaths. Bad idea. Another bad idea was getting some to make wreaths ourselves. The edge of my neighbor’s forests now have bittersweet scrambling up the trees, and a persistent vine in my yard needs an annual pruning because an errant seed went astray. 

It was Adam again who first gave me the trifoliate orange. That one is long gone because I could not appreciate tiny, sour lemons full of seeds and little juice. But it is a genuine citrus that produces lemons in Tennessee. We’ve made key-lime pie with them, used them to flavor jam, and whenever we need a very sour lemon. They are a mass of green, thorny branches and a novelty that could become a problem. A hedge would keep cattle in. Its another rootstock (for oranges) gone wild and is also knows as Flying Dragon, Tennessee Lemon, or Yuzu.

As I am from a farm near Chicago, and my likes have spread, I could be considered a non-native invasive. But I love plants and will continue to experiment with horticultural oddities. I suppose I’ll also continue spending the off-season, winter months managing our farm’s edges from unwanted plants, at least until it warms up enough to plant the ones we love. 

Bradford pear with invasive Callery pear in the background

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