If it were easy to get rid of invasive plants on a property, they wouldn’t be considered invasive, would they?
Lois Berg Stack, a Cooperative Extension specialist and ornamental horticulture professor at the University of Maine, described several non-chemical methods of combating invasive species during a lecture last month at the New England Grows trade show in Boston.
Some people might wonder why invasive plants should be removed at all. Many are attractive and were sold by nurseries for years. They grow easily on their own, so you don’t spend time tending them.
The problem is that invasive plants outcompete native plants, and native plants not only give a place its basic character but they support and feed native bees, birds and animals.
I once heard a lecturer equating invasive plants with junk food: they feed animals but they aren’t as nutritious as native plants.
The most common method of removing invasive plants is with the chemical glyphosate, sold under the trade name Roundup. Avoid it! First, Stack said, the World Health Organization has classified glyphosate as a potential carcinogen. (The European Consortium believes it probably isn’t a carcinogen, while the U.S. Environmental Protection Agency has yet to rule on it.)
Disagreement aside, it is always best to avoid chemicals when you can, and in some cases – near playgrounds and bodies of water – they are banned by law.
Realize going in that you can’t get rid of invasive plants in every case.
“You have to pick your battles,” Stack said, “You don’t take on a project that you know you are going to lose.”
An example is Japanese knotweed, which Mainers often call bamboo, though it isn’t. If it is growing on your next-door neighbor’s land, forget about clearing it from your property, Stack said. It is a plant that grows sideways – right into your yard.
In some cases it makes sense to leave the invasive plants in place. For example, if a steep hillside is covered with only invasive plants, mechanical removal could cause severe erosion, causing more damage than the plants themselves.
Fighting invasive plants is a two-stage battle. First, you have to get them out. Next, you have to keep them from coming back.
Invasive shrubs and trees like autumn olive, Norway maple, Japanese barberry, burning bush and glossy buckthorn resprout from their roots if you simply cut them at ground level.
Cutting back will keep them from spreading if you cut before the leaves form, but you won’t get rid of them.
To do that, you have to remove the roots.
Digging out the plants works sometimes, but that disturbs a lot of soil – which opens the way for more invasives to seed. In addition, you can’t always dig out the roots in rocky places.
A weed wrench or other root-pulling tools work on many smaller trees and shrubs, and Stack emphasized that all these tools will work better if you soak the soil the day before to loosen things up. Japanese barberry and multiflora roses are especially hard to remove because they have thorns.
Even if you manage to remove the big invasives, you’re still not done, as you must watch for the ones that get seeded.
Stack used to have autumn olives on her property, but she got rid of them. A patch of all autumn olives flourished across the street from her home. Every year, she has pulled the seedlings in her yard when they are just sprouting and are easy to recognize, pulling as many as 50 a minute.
It’s especially important to monitor areas under desirable fruiting plants like amelanchiers and crabapples, she said, because birds come to eat the fruit and expel seeds from undesirable fruit they have been eating elsewhere.
Norway maples are a big problem in our yard, because two of our abutting neighbors have them. My wife, Nancy, and I spend much of our weeding time pulling out the maple seedlings. In the wooded area where we don’t weed, we pull or cut small Norway maples in late fall, when they are easy to spot because they are the maples that still have leaves. To control our invasive tree seedlings, I mow or cut down those in the woods.
Weed wrenches usually don’t work on bittersweet, but they make it fairly easy to pull out the roots of small trees and bushes, especially if the soil is moist. Once the main plant is gone, the seedlings are easy to spot and weed.
For smaller weeds, like garlic mustard and coltsfoot, the answer is weeding for several years. The problem lessens over time, especially if you can get native ground-covers such as Canadian mayflower to replace the invasives.
Less labor-intensive tools are in the offing, Stack said.
Several universities are researching biocontrols – insects that eat invasive plants, and only the invasives. So far, one insect is doing a good job on purple loosestrife; another is keeping mile-a-minute vine in check.
Biocontrols that might be approved in the future would deal with swallowwort, which is a big problem in many Maine coastal towns; as well as phragmites, which are sweeping through Maine marshes; and Japanese knotweed. There is hope that we can push back the invaders.
One ecologically excellent, not to mention very cute, control is goats. They will eat almost anything and can reach steep areas where people and machines can’t go.
In many other New England states (but not yet Maine), companies rent out goats that can be penned into an area with the targeted invasive plants. When goats are used for several consecutive years, even if the plants resprout, the goats will eventually kill them. The city of Portland has toyed with the idea of employing goats for just such a task.
Stack, who showed photos of working goats during her lecture, said they are easy to tend and simple to move from area to area.
Would-be entrepreneurs: want to start a goat-rental business in Maine?
Tom Atwell is a freelance writer gardening in Cape Elizabeth and can be contacted at 767-2297 or at tomatwell@me.com.
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