In an earlier post here, I talked about the fun of finding volunteer plants, ones that you didn’t plant but are interesting and welcome in the landscape. In this post I’m on the other end of the spectrum – volunteers that are either invasive plants or noxious weeds, the ones that are at the very top of the priority list for removal and control.
The worst of these offenders are the true invasives. Did you know there is an official definition of “invasive plant”? To rank as an invasive, a plant has to be introduced to this country from elsewhere, it has to do significant ecological or agricultural damage, and the appropriate state authority must put the plant on its “Invasive Plant” list. Here in Massachusetts, that group is the Massachusetts Invasive Plant Advisory Group, which collaborates with the Commonwealth of Massachusetts Office of Environmental Affairs, and they have identified 35 species of definitely invasive plants and 31 species of likely invasive plants here. Another good resource for learning about invasive plants is through the Mass Audubon society, here.
In my yard, 5 of these invasives have settled in:
I dream of eradicating these plants from my landscape. It would be great to be able to spray them with an herbicide and have them just disappear. But they are tougher plants than that; when I have used herbicides in the past the plants slowed down a bit, but didn’t die. Because it is not that effective and because I try to avoid herbicides wherever possible, for me foliar spray is not a good option and I need a different approach.
In theory, by disrupting their growth and reproductive cycles enough, I can deprive the plants with food to support them and they will wither away. This starts with understanding each plant’s basic growth strategy. My 5 invasives form two groups – Garlic mustard and Dame’s rocket primarily spread via seed while Porcelain berry, Oriental bittersweet and Japanese honeysuckle primarily expand through root spread.
For the Garlic mustard and Dame’s rocket, the main strategy is to either manually remove them or cut the flowers early in the season before they go to seed. Each of these plants produces hundreds of seeds, and the goal is to get them out of the seed bank in your yard by letting them germinate, then not allowing them to reproduce themselves. This requires good timing and persistence, pulling plants or cutting flowers every year until the stand gradually diminishes; the seeds will persist in the soil for years. Fortunately, these two plants are relatively shallow rooted, so pulling them is not difficult, just tedious. Note that Garlic mustard is a biennial, so you have two chances to pull it out before it flowers.
The other three plants are tougher, and simply pulling them up doesn’t work because they will re-grow from small root segments left behind. So I use a combination strategy. Over the fall or winter, I scour the yard for the woody stems of these plants, use loppers or pruners to cut the stem down to the ground level, and immediately swipe an herbicide such as glyphosate right over the cut stem. The plant will absorb the herbicide which will at least partially kill the roots. The roots are tough, though, and will try to re-grow, so during the next growing season I will go around the yard during the early summer and cut back to the ground any new growth I see. After July I let the growth continue, so I can find the woody stems for my next winter’s cut-and-swipe. Using this approach over several years, I have greatly reduced the amount of these plants in the larger part of the landscape. Of course, these plants also have seeds, so there is always the possibility of new infestations. I remain aggressive in controlling these plants but now it is more like regular weed pulling.
These are plants that act like invasive plants but are either natives or not on the official list. But they spread rapidly over the landscape or have characteristics that I won’t tolerate in the yard, so I am aggressive about managing these plants too.
In the past I have tried herbicides to control or eradicate these plants, without much success. My primary strategy is manual removal, either pulling the plant with roots where I can or cutting them off at ground level. Mug wort, red sorrel, and bindweed have extensive underground root networks, so the best I can do is cut them back hard (and pull as much root as possible) during the growing season to reduce the plant’s ability to photosynthesize. Thistle and poison ivy can’t be touched, so I use loppers or pruners to cut them to the ground. Orchard grass is easy to remove in the late winter or early spring; the roots of the grass clumps have died back so they come up readily. If I have also remembered to cut back the grass seed heads in June, then the next year’s grass crop will be much reduced.
Blackberry is an interesting problem. On one had, it is a native and actually produces edible food, so it can be a valuable plant. But in my landscape, it crops up everywhere, is full of nasty thorns, and I never get the fruit because the birds get there first. So in the tended part of the garden, I consider blackberry a noxious weed and remove it regularly by cutting it to the ground. In the wilder places of the landscape I let it go, and I’m reconciled that birds will probably spread some of the seed around for next year.
Disposing of the cut or pulled plants is a bit of a challenge. It’s not cool to dump them in either the town’s compost system or your own, as these systems may not completely kill the plants or seeds so you are just spreading those problem plants around. Some experts recommend bagging them and disposing them with the regular trash. I have done that despite the regulations that say “no garden waste” in with the trash.
This year I am trying something new. The section around my compost pile is covered with black plastic this year in an attempt to kill vegetation that was overwhelming that area (I don’t get excited about weeding my compost pile!). So the invasives and noxious weeds that are cut are dumped on top of the plastic to bake in the sun until they are dead and brown. The Garlic mustard and Dame’s rocket, with their seedheads, are put in black plastic bags and left to bake for weeks. At the end of the season, I will gather all of the remnants up and put them on the compost pile. At this point they shouldn’t be able to contaminate the garden beds where they will end up.