Henry Homeyer: getting rid of invasives

By Henry Homeyer
©2019 Telegraph Publishing LLC

My mother used to say, “The road to hades is paved with good intentions.” That is particularly true for gardeners and plant collectors. Most of those nasty invasive plants we struggle to eliminate from our landscape were brought here from abroad by people who didn’t know better. They thought the plants would be a useful addition to their landscape. Plants such as barberry, Japanese knotweed and burning bush looked great to them. What they didn’t bring, of course, were the insects that eat them and keep their numbers under control in their native environments.

January is down time in the garden, generally. We can’t plant anything, and often the snow is deep. But if the January thaw has melted away the snow and ice where you are, this is a time when you could work on getting rid of some invasive trees and shrubs.

Actually, what I have I mind is helping to reduce the vigor and number of mature plants by cutting them down. That won’t kill them, but will keep them from producing seeds next year or even longer. Most invasives have roots that will send up new sprouts, come spring. And winter is not a time when you can dig up or pull out roots. But cutting them down and burning them is a chore you can do now.

The first task you have in this effort is to learn to identify the plants. For me, the most common invasive plants in the woods around my home are bush honeysuckle and barberry.

Invasive bush honeysuckle can get to be 10 to 15 feet tall and wide. It has fragrant white blossoms in June and oval-shaped leaves that are opposite each other on small twigs. In winter the bark is distinctive – slightly shaggy with distinctive ridges. If you cut a stem, there is a hollow spot in the center of the stem, though it might only be the diameter of a pencil lead. The shrub produces red or orange berries.

Japanese barberry is a tough plant that I have seen in deep woods, far from homes or roads. In full sun it produces massive quantities of red berries that birds eat and then drop the seeds all over. The bush has small green or purple leaves and is dense with thorns. I visited a barberry hedge recently, and it was still loaded with berries. The best solution is to cut it down now, and dig out the roots in the spring.

Burning bush (Euonymus a) is on invasive species lists throughout New England, even though I rarely see seedlings in the woods, and have none on my property. It is best identified in the fall, when its scarlet leaves are noticeable. It is more of a problem in Rhode Island, Connecticut and Massachusetts. I once saw a bumper sticker that said, “30 Below Keeps Out the Riff-Raff. I assume it was talking about plants like burning bush which survives here, but doesn’t spread as fast as it does in warmer climes.

Buckthorns are small trees or large shrubs that are very difficult to eliminate. If you cut one down, the root system will send up many, many new shoots, come spring.

There are two different species of buckthorn common in New England: common buckthorn (Rhamnus cathartica) and glossy buckthorn (Rhamnus frangula), a smaller version with pretty shiny leaves. Both produce berries that turn a deep purple and are the size of blueberries, put with a pit in the middle like a cherry.

You can kill these two by double girdling the trunks with a hand saw, cutting through the bark and green cambium layer while avoiding the dense heartwood. By double girdling, I mean cutting two lines all the way around the stem a foot apart or so. If you do it now, the plants will leaf out and grow normally this year, and perhaps even next year, but then they will die – without sending up new shoots. I have done this.

By cutting through the cambium layer, no nutrients will be sent to the roots, and the roots eventually starve. Common buckthorn is often multi-stemmed with stems close together, so getting a saw in around each stem can be difficult.

There are several reasons we both with all of this. First, although birds may eat the berries of invasive plants and distribute their seeds, they did not evolve with the plants and often do not benefit much from what they eat. The invasives also out-compete many of our own native plants. They leaf out earlier in the spring and drop leaves later in the fall than our natives. They often shade out or disrupt the growth of wild flowers, too.

Invasive trees and shrubs may be less attractive to the caterpillars that feed on our native trees and shrubs, and which are such an important food source for baby birds. Butterflies and moths lay their eggs on the leaves of native woody plants so that their caterpillar babies will eat well. Those caterpillars make up the vast majority of food for nestlings, even those species that develop into seed eaters. So avoid growing invasives.

Take advantage of the January thaw – or a thaw anytime this winter – and remove some invasive plants. Get a burn permit, some marshmallows and do your woods some good, and have fun!

Henry is the author of 4 gardening books. He is away this week, and not answering gardening questions.