In the Garden This Week: Let's Talk about Invasive Plants

First a funny/weird experience this week: I was harvesting potatoes and at about 3" deep in fairly fine soil, I came across one that looked rotten, all brown and black and with a little green in it. I was ready to dig it out and dispose of it, when I noticed on closer examination, that it was BREATHING! I carefully stuck my trowel underneath it and lifted it out and a toad hopped happily off. I guess he was cooling off down in the soil! It is unlikely adventures like this that make gardening interesting.

Invasive plants, especially perennials and trees, are plants that spread where we do not want them to be. They also can be plants that are difficult to control and to keep where we want them. One of the things that makes this discussion difficult is to understand that the word "invasive" means different things to different people. There are few nationally accepted standard definitions and the variety of state classifications are not at all consistent. I found, in researching this topic, that several states, like New Hampshire, have a specific list of plants that cannot be sold or purchased in that state. In addition, what is sometimes considered an invasive in one state is labelled as an "alernative to an invasive" in another state.

Every homeowner deals with invasives and some of them we really like to have in our landscape. That is all well and good as long as we recognize the potential for them to spread unless we can control them.

Invasives plants are often purchased in nurseries and, of course, there is nothing on the tag that suggests that this plant or that is an invasive. We really need to educate ourselves better before purchasing plants. Another aspect to think about when we purchase a plant or tree is to consider the ULTIMATE height and width of the plant. We have a tendency to plant our purchases too close together and then a few years later we wonder how we can move them to spread them out a little.

There are several ways that an invasive can be spread around your yard or garden. Some plants like strawberries or bamboo can spread a considerable distance by roots or rhizomes that move underground and reappear where they are not wanted. Another way invasives spread is by seeds flying off base plants and landing in fertile soil. A neighbor recently had about 100 small plants growing in his yard and fouling up his well-groomed yard. We did some research and determined that they were black locust tree seedlings. And where did they come from? An analysis of the trees bordering his yard showed that there were exactly NINE black locust trees on the border in a park and in a vacant lot next door. So he was going to have a forest if he didn't do something about these seedlings. The natural tendency among many of us is to ask what can be sprayed selectively (not to kill the grass) on the seedlings to eradicate them. In this case the best advice was simply to mow the seedlings a little closer than the grass is normally mowed and that seems to be a viable solution, although this problem can easily return.

A final way that invasives can be introduced into the landscape is by birds. While is a very useful task to plant bushes that have berries, (a great environmentally-friendly idea), and many of those berries have seeds and when the birds excrete these seeds they usually fall into the ground and before you know it you have a new plant struggling to survive in the landscape. Some of these are very aggressive and if not removed, will sprout rather quickly. In my yard the Japanese walnut trees are sort of invasive because the squirrels can't seem to remember where they planted those walnuts last fall. I started with four Japanese walnut trees and I now have 14, some of which are 25-30 feet tall.......and I LOVE them!

A few examples of invasives that can be spread by the birds include one of the feature invasives that many of us (including the author) have in our yard. It is Burning Bush, which gives us such beautiful fiery red foliage in the fall. If you have Burning Bush, you probably have more than one. Another well-known similar plant is Oriental Bittersweet. This one is very damaging. It grows very fast and because it winds itself around trees and bushes it strangles them and they die. Bittersweet very much needs to be eradicated when found in the landscape and it can be cut near the soil and then carefully spray the stump with an herbicide containing glyphosate (like Round-Up). Just remember that Round-Up is a systemic herbicide and it will kill anything its spray touches, so use it carefully and in small amounts, if you have to. Do not pull the bittersweet out of the tree or bush. Leave it alone for a while until it dies off. It will be much easier to remove then.

There are a large number of invasives and some of these may surprise you because you have had them in your landscape for years. Here is a partial list of a few of those considered to be invasive:                                                              Multiflora Rose/Butterfly bush/ Autumn Olive tree

Privet/ Black locust tree/ Bamboo            

Hollyhocks/ Mountain bluet/ Rose Campion

Purple Loosestrife/ all the Brooms/ Cotoneaster

Japanese Wisteria./ Japanese Honeysuckle/ Bayberry

Norway Maple tree/ Canadian thistle/   Rose of Sharon

And then there are the weeds that we often deal with:

Aegopodium (goutweed)/ Moneywort/ Wild Garlic

Sheep sorrel/ Garlic Mustard/ Black Knapweed

Nutsedge/ Knotweed/ English Ivy

Crown Vetch Baby's Breath

These lists are merely samples of what are considered invasives in various locations. As I said many of us are very happy with them and that is good. Just be careful that they do not spread all over your landscape. For some of us it is a difficult task to dig out and dispose of any plant. But we have to get over that if we want to have the best landscape possible.

In a future blog I will discuss what are considered some viable alternatives to many of these invasives. Stay tuned for that column coming up.                           

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A reminder about our Gardening Information and Soil Testing Kiosk at Paradise Valley Park in Middletown (Prospect and Paradise Avenues) every Sunday until the end of September (rain or shine) from noon to 2 pm. Bring plant or insect problems for analysis or just come to talk to us about our mutual favorite subject: the home garden. Our kiosk is a volunteer project of the URI Master Gardener program.

You can also contact us by e-mail at  gardeninginformationri@gmail.com with any gardening questions.