Over the last century and more, we humans imported plants that do great harm to the natural balance of plants and animals—and to ourselves. Invasive species, plants and animals, are considered one of the prime causes for species extinction because of their ability to out-compete and displace native species.
Repairing the damage caused by unrestrained growth and spread of invasive plants sometimes appears impossible. Invasive action teams in Granby tackled tough areas at Holcomb Farm over the last 18 months and have completely transformed them to sites of beauty and natural health that will require far less attention to maintain into the future. In the process, plenty was learned about how to have a big impact with limited resources. These lessons are useful for anyone working to bring an invaded area under control. For more detail and photos, visit GranbyInvasivePlants.weebly.com
Free the Trees
It’s exciting to liberate, with hatchets, hand saws, loppers and chain saw, majestic trees that are relentlessly engulfed by vigorous Japanese bittersweet vines. Cutting the vines as high as possible and leaving the trunk clear makes it possible to follow up if vines start up again. There’s no way to completely pull vines that are already 20 or 40 feet up—they have to rot in place gradually over several years before they are completely gone.
Trees completely blanketed with vines won’t recover and need to be cut down along with the vines. Those that are partially covered may be worth saving by cutting off the dead sections and freeing the healthy parts—it’s a judgement call often guided by the shape of the surviving portions and how realistic it is to protect it from inevitable invasive attacks into the future.
Nearby bushes, shrubs and smaller trees are often vine launching pads. Sturdy multiflora rose, autumn olive or honeysuckles are invasives that should be cut to the ground and pulled by the roots, or cut repeatedly until their roots can no longer support new growth. But some vine enablers are desirable natives such as dogwoods, cherries, willows, crabapples and others that can flourish when invasives are removed. It’s more work to preserve these than to cut them down—repeated attention is needed over time so that vines don’t get reestablished—so planning and accurately identifying them is crucial.
Yank the Plants
All invasive plants start small, and it’s way easier to pull them out by the roots before they build stronger connections to the earth. It’s completely doable to pull young bittersweet, MF rose, Asiatic barberry, winged euonymous, garlic mustard, mugwort, purple loosestrife and wineberry, for example, and much harder to eliminate them when they get larger. Learn to identify these plants when they are young—a couple inches to a foot high—and the best ways to pull them, roots and all. Some require gloves; others break easily above the root and are best pulled when the soil is moist and the grip is firm and gradual. Once pulled, letting the hot sun dry them out in shallow piles is usually enough; but if they have flowered and seeds are present, burning them or bagging and disposing of them reduces next year’s labors.
Cover the Earth
Invasive plants succeed because they are terrific at procreation: seeds tend to last several years and all they need is light, water and a bit of soil to launch new generations. Leaving bare soil is throwing out a welcome mat to invasives and native weeds. Commercial mulch is a great way to cover the soil and deprive seeds of light, but more may be needed. Rather than pulling every last bittersweet or garlic mustard seedling, for example, smother them with layers of cardboard, heavy craft paper or newspapers, covered with mulch or woodchips. In a few months, the layers will break down and native alternatives can be planted in holes, leaving the layers in place. Plastic sheeting, landscape fabric and mulches that shed water also smother seedlings, but they don’t enrich the soil and often make it harder for desirable plantings to access the water they need.
Follow-up — Again — and Again
They are good at what they do, those invasive plants, and while our attention shifts to other things, they are recovering and rejuvenating. Cutting mature bittersweet vines, for example, often stimulates ultra-vigorous new growth that rapidly shinnies back up tree trunks—10 feet or more per year. Pulling every single garlic mustard or dame’s rocket one year can seem pointless when the same infestation appears the next. The good news is that it’s not hopeless; the bad news is what it takes.
The new sprouts from mature invasive trees, shrubs and vines with extensive root systems can be cut every year, even several times a year, for several years, to diminish them in strength over time—slowly. Quicker methods include pulling out by the roots (often requiring heavy hand or power tools); solarizing with clear or black plastic (see the June Not Wanted column); and careful cut-and-paint strategies, especially in late summer and early fall, with liquid herbicides.
Smaller invasive plants, like garlic mustard, purple loosestrife, and dame’s rocket (that spread mainly by distributing seeds) can be defeated by faithfully pulling and destroying every one for several years. For plants that spread mainly by rhizomes (horizontal roots that burst through the soil as new plants a few inches from their parents) like mugwort and Japanese knotweed, prevention is the best strategy. Carefully pull every single invader to prevent them from becoming established. Once established, solarize or use chemicals on these really tough customers.
For information about Granby’s invasive action successes, specific invasive plants, control strategies, pictures and resources, visit GranbyInvasivePlants.weebly.com