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The answer to the question about the best time to remove invasive plants is: It depends! Timing is important when working with invasive plants. Some are easily removed in early spring, when the ground is moist and the plants are small. Others are more easily identified later in spring or in summer, when their flowers are in bloom. Still others will spread if treated too early in the growing season.
Planning your work with invasives will reduce the effort needed in the future. Invasive plants are survivors, and they will return if they aren’t monitored for regrowth. Proper timing of removal is the best way to combat regrowth. Here are some pointers.
First, tag those early leafing woody plants. Barberry, honeysuckle and others will leaf out earlier than most native plants. Woody plants spend their stored energy on growth in the spring. Trying to remove them at this time will encourage more growth. However, a small sprout may be removed if the soil is moist and the entire root is removed with the sprouts. Typically, invasive plants will regrow from bits of root left in the ground. These new shoots are often more numerous than the original invasive plants, so just digging or pulling a woody invasive plant in the spring may create an even denser area of unwanted plants later in the year.
Some herbaceous plants may be safely pulled when they begin to sprout and the soil is moist. Again, strive for complete removal of the roots or regrowth may occur. Canada thistle is a good example. Its roots are shallow in the spring and more easily pulled at that time. But root fragments will resprout. Mature thistle plants can be controlled by removing the flowers before seeds form. This will not eliminate the invasive plant, but it will reduce the seed bank from which the next generation will emerge.
Garlic mustard is easily identified in May and early June by its tall stems with small white flowers and its garlicky scent. Pulling the plants when they bloom will reduce the formation of seeds and prevent new plants from germinating next year. Bag the pulled plants and dispose of them in the trash. Continue this process for up to five years, until the seed bank is exhausted.
Plants such as purple loosestrife, black swallow-wort and ornamental jewelweed (a taller, pink-purple flowering weed than our native orange-flowered jewelweed) bloom in the summer and are easily identified at this time of the year. Control methods vary for these plants, so care is needed when attacking them.
Those woody invasive plants that were tagged in the spring are best tackled in the later part of the growing season. After they stop growing for the season, they begin to pull nutrients into their roots. Wait for the late summer and autumn to work on bittersweet, honeysuckle and multiflora rose. Details for controlling these woody-stemmed invasive plants vary from one type to another, but all need your patience for the best timing of control measures.
Japanese barberry responds well when you cut the branches down to the root crown, then use a weed torch to sear the remaining crown ends. Multiflora rose also responds well to the weed torch method. The weed torch is not as effective on bittersweet and honeysuckle. These woody plants may require the “cut and dab” treatment with a strong herbicide.
Regardless of the type of plant or the control method, no method is guaranteed to be 100% effective. Monitor the area for regrowth and repeat control measures as needed. Many invasive plants require several years of monitoring to ensure eradication. Don’t give up! Recognize, remove, replace with native plants, and repeat as needed.
For more information about invasive plants, go to the Harpswell Invasive Plant Partnership’s website at hippmaine.org or the Maine Natural Areas Program invasives page at tinyurl.com/me-invasives.
