Invasive Plants

Gary Westlake


When I first heard of Dog strangling vine, I had a premonition that our little dog was in deep trouble. It sounds like a nasty way to go, and I am fairly sure he would not be able to outsmart such a plant. Dog strangling vine has invaded large areas in the US at the eastern end of Lake Ontario and has been found in Canada. This vine is related to milkweed so much so that monarch butterflies will lay eggs on it, but the young do not survive. You can recognize it by its slender green pods and it has no natural predators.

It's poisonous to deer, goats and other grazing animals. It grows in stands as big as 500 acres, crowding out all native plants and it has been found not far from here!

Many of you have a bush or tree on your property known as European Buckthorn and you may not even know it is there. It looks harmless, but it is not. If left unchecked, it will take over. In stands of one or two young trees or shrubs, they look harmless and almost handsome with their strong, clean foliage and dark berries. Unfortunately, the unsuspecting homeowner who leaves these visitors from the underworld to their own devices is in for a major battle. We have spent the last five years fighting this beast on our property.

Iíll bet most of you know that purple loosestrife is a serious threat to our wetlands and probably many of you have seen the sea of pink that marks an infestation. It is not certain how purple loosestrife was first introduced but one possibility is the import of seeds or rootstock for early 19th century gardens. No gardener intentionally introduces an invasive plant into nature, but it is hard to decide how to avoid it.

Invasive plants are species that are not native to a region. Invasive plants have the ability to compete with, and replace, native species in natural habitats. They have no natural controls. Not all invasives are foreigners. Manitoba Maples have become invasive because they seed readily in disturbed urban areas. Milkweed has spread because of the deforestation that preceded development and farming.

There are plants that are not so much invasive as they are garden thugs. Here is the dilemma - you want a vigorous plant so that it doesnít die on you and it doesnít take forever to look the way it does in the magazines, on the other hand, you donít want one that will take over your garden and start working on the world. Because letís face it no one wants to be the cause of the next purple loosestrife.

I am convinced that any plant that encounters just the right conditions for optimal growth and reproduction, can become a garden thug. There are parts of the world where major hacking back is required to keep wisteria from tearing down garden structures with the shear strength of its trunks, whereas here, there is a civic holiday declared when one of our pathetic little wisteria vines gives birth to a flower or two.

Plants align on a continuum from garden thugs and invasives to garden wimps (which usually means you are trying to grow them where they donít belong). I am still learning, but the art of it seems to be to locate plants where they are happy but not too happy. Just for fun we planted Iris pseudoacorus which at the waters edge goes crazy and takes over. In our garden it was in a drier spot, so it struggles but it still is twice as tall as other irises and makes a grand statement.

The annual spring rite of plant sales is fraught with dangers for the uninformed. You can bring home something that is not necessarily invasive like purple loosestrife or European buckthorn whose mission is to destroy the world. The plants you sometimes find at the sales could be better labeled as assertive. You may spend more effort than you bargained for keeping them off the path, out of your grass and where you want them to stay. If you are buying from the plant sale, choose carefully and if you are donating, consider composting your excess goutweed, ribbon grass, lily of the valley and periwinkle. They are the gifts that keep on giving.

Periwinkle is a popular choice for ground cover. It is handsome and even grows under Norway maple, which by the way is also a foreigner Ė and belongs in Norway. One way to deal with the issue effectively is to plant native plants. For example, there is nothing more beautiful than the native pagoda or alternate-leaf dogwood or the native maple.

The smell and beauty of lily of the valley is seductive. They are the sirens of the plant world. But no matter how much you pull them, they keep popping up around the walk, in the grass, under the walk, and through the walk. Even if I spend my last breath digging them out, long after Iím gone they will be still here reminding the world that plants rule!