Have you been wondering why your invasive plants keep coming back? Or whether your trees will die when bittersweet vines climb all over them? The Harpswell Invasive Plant Partnership wants to help you get to the bottom of these questions and more.
First, about those invasives that keep coming back: The key is in the details when deciding when and how to eradicate them. For example, spring is the best time to get rid of Canada thistle because it’s easy to identify in the garden, and the roots come out most successfully when they’re small and the soil is wet. Pulling straight up with two hands gripping the plant’s base will remove enough of the root to discourage regrowth. Using the same method later in the season often breaks off the stem without removing enough root, allowing the plant to keep growing.
Garlic mustard is also easier to conquer in the spring. Its white blooms are easy to find in May, when most plants are not yet in flower. It is easily pulled out of the ground at this time. Waiting longer into the season invites seed production, as each plant can produce several hundred seeds that remain viable for up to six years. This method will need to be repeated annually for a few years.
Summer is a good time to dig out bull thistle because it’s not easy to find in spring. By summer, the large thistle heads at the top of its spiny stalks are obvious. They should be cut 2-4 inches below ground to discourage regrowth. When these thistles open and disperse up to 300 seeds per plant, it’s too late to address them. Monitoring the area and cutting annually is necessary because there are already seeds in the ground.
Yellow iris is another plant to control in the summer. The stiff leaves, up to 1.5 inches wide, and yellow flowers from May until July indicate that it’s time to dig out the entire plant, ensuring every root is removed to prevent new plants from growing. Digging when you first identify this plant will prevent it from developing its 2-inch-long seed capsules, which contain about 120 seeds each.
Notice that the invasives mentioned so far are soft and fleshy compared to hardwood shrubs and vines, and they can be controlled by pulling and digging. This seasonal approach to invasive controls will help you avoid becoming overwhelmed. Save your energy for fall, when it’s time to cut and dig out burning bush, barberry, multiflora rose, and honeysuckles. Although you could dig out these hardwoods as they emerge during the growing season, spreading out the work will make your task less burdensome.
Bittersweet deserves special mention because it quickly overwhelms and can kill neighboring trees. Cutting this vine early in the growing season promotes root sprouting at every root node. Where you start with one vine, you’ll end up with a whole circle of new plants the following year. For this reason, in the fall, you will need to immediately dab the cut of this vine with a dot of herbicide.
For more information, visit the website of the Harpswell Invasive Plant Partnership at hippmaine.org.
