What to do about invasive species in your garden



Since ancient times, explorers have brought back seeds and plants from exotic lands. Some, like the apple, have been a boon to the citizens of their adopted home. Others, like the famous Japanese knotweed (aka “bamboo”) have been more of a headache than a godsend.

New England, with its cold climate, has a natural defense against certain invasive species: our winters. But many more have settled in and are taking over – or trying to do so. It is up to us, the gardeners, to be responsible: we must learn what the problematic plants are and we must get rid of those that grow on our property.

Invasive plants reproduce quickly and invade wild habitats, supplanting plants that Mother Nature provided by stealing light, water, and nutrients from less aggressive plants. By definition, they are exotic species – plants from other countries. These plants are often very beautiful, but they are botanical crude.

Most invasive species produce large numbers of seeds which are distributed by birds, wind or water. In most cases, invasive species are also difficult to remove or eradicate once established and have extensive root systems that make it difficult to simply pull them out.

Japanese knotweed is an invasive species that is almost impossible to dig up.

Back home, in their country of origin, most invasive species have predators – insects or diseases – controlling their numbers. They may have come inadvertently or may have been brought in by well-meaning people who thought they were pretty or needed them. Some, like the burning bush, barberry, and Norway maple, were introduced and sold because they are essentially indestructible and pretty.

For starters, you can learn how to identify species that are prohibited in your state and eliminate them on your own land. Check with your local university extension service for a listing for your state.

Getting rid of invasive species, however, may not be easy for two reasons: You may like the invasive species and you may have planted it before you know better. Second, it may not be easy to remove, even with the use of herbicides (which you probably don’t want to use anyway).

Norway maple, for example, is a beautiful tree that grows quickly and survives well even in urban areas. It will grow in the sun or partial shade and is not bothered by road salt. If you have one shading your house, I can understand why you might not want to cut it.

If you are a city dweller, you can assume that since there are no forests nearby, it shouldn’t matter if you keep your Norway maple (or other invasive species). But it is not just the wind or the birds that distribute the seeds. Runoff can carry seeds to an outlet in a natural environment. The seeds of your tree can end up in streams, rivers, ponds. So even city dwellers can make a difference in helping to control the spread of this invasive tree by cutting down their own.

To see if the maples growing in the wild near you are Norway maples, take this simple test: break a leaf at its attachment point and look at the stem. If it oozes a milky sap, it’s a Norway maple. The leaves also tend to be wider and taller than sugar maple or red maple leaves.

For organic gardeners, getting rid of invasive plants isn’t easy. For herbaceous weeds, consider the lawn mower. Once you’ve removed the stems (and as much of the root mass as possible), plant some grass seeds. Mow it weekly and the roots will not be recharged. The stems will continue to grow for years to come, but if you mow them you can win.

Invasive barberries produce berries eaten by birds in winter, but they drop seeds everywhere.

Digging the stump of an invasive shrub like barberry, honeysuckle, or burning bush is a pain in the neck, but you can probably do it. Digging the stump of a large Norway maple is impractical. But there are people with backhoes and stump trimmers who have the expertise to do it.

Several brands of weed wrenches are available to help you pull out small trees and shrubs.

If your woods are full of small, invasive tree or shrub seedlings, you may want to get a sapling pulling tool called a weed wrench. This tool has a mouth-shaped gripping part and a long handle to provide leverage. The right size weed wrench allows a 150 pound office worker to pull up shrubs and small trees that would not be possible to pull out otherwise.

Why bother digging up invasive species? You can decide to do it for the good of your grandchildren or for the environment. Even in states with good laws prohibiting the sale of invasive plants, no one can force you to cut or pull up your invasive plants. But being a little selfish is also good. Think about all the great plants you can buy and plant if you get rid of these invasive species. And think how wonderful it would be if wildflowers and native plants started to bloom in your woods.

Henri homeyer

Henry Homeyer’s blog appears twice a week on gardening-guy.com. Write to him at PO Box 364, Cornish Flat, NH 03746. Please include a stamped envelope with your address if you would like a reply by mail. Or send an email to henry.homeyer@comcast.net.


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