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Spotting Invasives

11/16/07 5:55PM By Henry Homeyer
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Henry Homeyer, commentator
(HOST) Commentator Henry Homeyer says that this time of year it's easy to tell where native trees and bushes are being crowded out by invasives - and it's a good time to do something about it.

(HOMEYER) When I tell people that invasive shrubs are taking over the understory of our forests, most just think I'm being an alarmist. But I'm not. This is a time of year when you can see for yourself.

Here's what to look for: As you drive down the road look for shrubs that are still showing green leaves. By now most of our native trees and shrubs have dropped their leaves. Young beeches and oaks hold onto their leaves throughout the winter, but those leaves are mostly brown by this time. The invasives, on the other hand, are still green and busy using the sun to build up their strength - and store up energy.

Two of the most common invasives in my area are bush honeysuckle and common buckthorn. Both still have green leaves, which gives them an advantage over our native species, which are dormant.

The honeysuckles are big, sprawling bushes that can grow to be 10 feet tall and wide. They produce yummy red berries - yummy to birds, that is. The birds eat the berries, fly somewhere, and deposit seeds that will grow into new plants. The bush honeysuckle was introduced from Asia, where it has natural enemies - but here there aren't enough enemies to keep it in control.

Common buckthorn, like the honeysuckles, will grow in sun or shade, under wet or dry conditions. It's a small tree, only getting to be about 25 feet tall. But it's hard to kill a buckthorn because if you cut one down, it sends up several new shoots from its extensive root system.

Pulling them out when they're still young is the best control. Girdling their trunks with a saw can slowly kill them, but you need to slice through the bark twice, about a foot apart, cutting two rings around the tree. And, I've been told, you shouldn't cut deeply into the trunk or you may trigger the roots to send up new shoots. Just slice through the bark and the cambium, that green layer beneath it. I tried double-girdling a buckthorn last fall, and this year it had just a few leaves. Next year it should be dead.

So, as comic book character Alfred E. Neuman often said, "why worry?" You should worry because invasives will shade out our native wild flowers and understory plants. If you enjoy seeing trillium or Jack-in the pulpit in the spring woods, you need to get rid of honeysuckles and other invasives. Some invasive species produce food for our wildlife that is less nourishing than that produced by our native species. Invasives are, in a sense, popsicles for our birds - tasty but not very nutritious.

Now that my work in the garden is about done, I'm working on eradicating the invasives that continue to spread throughout our woods. Sometimes I just cut down the honeysuckles, knowing that they will re-sprout in the spring. But I feel like I'm making progress because those little shoots won't be producing seeds for at least a few years.

Henry Homeyer is a garden writer and columnist. His new book is "The Vermont Gardener's Companion: An Insider's Guide to Gardening in the Green Mountain State".

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See Henry Homeyer's invasive photos
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