What You Need to Know About Invasive Plants

Many are handsome, and all are hard to eradicate

Since ancient times, explorers have brought back seeds and seedlings from exotic lands. Some, like the apple, have been a boon to the citizens of their adoptive home. Others, like the notorious kudzu vine that has taken over parts of the south, have been more headache than boon. New England, with its cold climate, is blessed with a natural defense against kudzu and some other invasives: our winters. Unfortunately, there are plenty of invasives that like it here.

Barberries come in green and purple leaved cultivars. All are found wild in the woods now.

 Invasive plants are those that reproduce rapidly and take over wild habitats, out-competing the native plants that Mother Nature provided, stealing light, water and nutrients from less aggressive plants. By definition, they are alien species, plants that have come here from other countries. These plants are often very good-looking plants, but thugs.

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Most invasives produce large numbers of seeds that are distributed by birds, by the wind, or by water. In most cases, invasives are also difficult to remove or eradicate once established, and have extensive root systems that preclude simply pulling them up. 

Garlic mustard is a biennial that releases a toxin into the soil that inhibits tree growth by killing beneficial fungi.

Back home, in their country of origin, most invasives have predators – insects or diseases - that keep their numbers in check. They may have come inadvertently in the ballast of sailing ships, or been brought by well-intentioned people who thought they were pretty or had some use for them. Some, like burning bush, barberry and Norway maple, have been introduced and sold because they are essentially indestructible – and pretty.

 What can you do? For starters, you can learn to identify the prohibited species in your state, and eliminate them on your own land. Go online to obtain a list for your state, or go to the website of the New England Wild Flower Society, http://www.newfs.org. This is a fine organization that is doing much to promote native species and educating the public about invasives. At their web site you can be connected to each state’s list of invasive, prohibited plants.

 Getting rid of invasives, however, may not be easy for two reasons: you may like the invasive species, and may have planted it before you knew better. I have friends with a big Norway maple that was given to them by a loved one. They don’t want to cut it down, and I understand that. Still, I do hope they will cut it down.

Norway maple planted on the Lebanon, NH green.

Secondly, it may not be easy to eliminate your invasives– even with the use of herbicides (which you probably don’t want to use anyhow). Many invaders have very extensive root systems and will re-sprout if simply cut down.

Japanese knotweed can send roots down 8 feet iinto the soil.

The Norway maple, for example, is a lovely-looking tree that grows fast and survives well even in urban areas. It will grow in sun or partial shade and is not bothered by road salt. Each year a mature Norway maple produces thousands of seed pods.

 Runoff can also carry seeds through subsurface drainage systems to an outlet in a natural environment, even if your tree is in a city. Seed from your tree can end up in streams, rivers, ponds. Thus even city dwellers can make a difference, helping to control the propagation of this invasive tree by cutting down theirs.

 Some people don’t believe that “Crimson King”, one of the most commonly sold cultivars of Norway maple, is a problem. It has rich red-purple leaves – but these leaves are never seen in the wild. Apparently all Crimson Kings are clones of one plant that had a genetic mutation. But usually when they produce seed, the seeds produce green-leaved progeny.

You should also know that if you do cut it down your Norway maple, your lawn and gardens will do better. All maples, but Norway maples in particular, send roots far and wide, and suck the water and nutrients out of the soil – making life tough for other plants.

Norway maples show white sap oozing from petiole when you snap off a leaf.

To see if maple trees growing wild near you are Norway maples, do this simple test: snap off 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 broader and larger than sugar or red maple leaves.

 What are some other popular and common invasives you can work to eliminate? Bush honeysuckle, barberries of all kinds, burning bush (that fall favorite with bright red leaves), autumn olive, buckthorn, privet, oriental bittersweet and multiflora rose.

Buckthorn are showing berries right now, in Septmeber

Digging out invasives is the best approach, getting them when they are young. Cutting them down prevents them from producing seeds, but often stimulates them to send up many new shoots, compounding the problem in the long run.

Wheeled shrub puller uses simple mechanical advantage to pull large shrubs

Learn about the shrub puller invented in Woodstock, VT and pictured above  by clicking here. 

 You may decide to eliminate invasives for the sake 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 down or pull out your invasive plants. But think of all the great plants you can buy and plant if you get rid of those invasives!

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Want help in your garden? I make house calls - consultations - to help you plan and improve your gardens. Call me at 603-543-1307 or e-mail me at henry.homeyer@comcast.net 

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