Although the ability to spread rapidly sounds good when you're looking for new ground covering plants, the invasive species just don't know when to stop. This is bad news for native plants, because the invasives create such thick mats that they smother, outcompete and kill the good vegetation. Once established, it's difficult to completely eradicate invasive ground covers without using potentially harmful chemicals, but using manual and mechanical control methods on young plants offers some control.
The best way to control invasive ground covers is to prevent them from occurring in the first place. You can inadvertently spread problematic plants by using:
- contaminated seed, soil, gravel or mulch.
- unclean gardening tools.
- invasive seedlings bought at a nursery.
Do your part to make sure you don't introduce alien plant species into new areas by:
- keeping gardening equipment clean.
- using seed mixes certified as "weed-free" from reputable sources.
- promptly treating new infestations.
- not sharing invasive plants with other gardeners.
- containing invasive plants you want to keep in your landscape.
- replacing invasive ground covering plants with native or non-invasive species.
- disposing of invasive plant debris properly.
When shopping for ground covers, avoid purchasing and planting plants described as "self-seeding," "fast-growing," "no-care," "spreading" or "vigorous." All of those indicate the plant is probably invasive.
Containing Invasive Ground Covers
Nurseries and garden centers commonly sell well-known, invasive ground covering vines, such as English ivy (Hedera helix, U.S. Department of Agriculture plant hardiness zones 5 through 11), common periwinkle (Vinca minor, USDA zones 4 through 9) and big periwinkle (Vinca major, USDA zones 7 through 9). If you'd like to keep those plants in your landscape, take responsibility for keeping the plant contained to its growing area. This might mean:
Disposing of Invasive Plant Debris
Ensure you remove all plant debris from a treated area and dispose of it in the proper manner. This can include making a compost heap only for invasive plants that haven't gone to seed. Keep an eye on the pile and remove any sprouting pieces. Never, ever use this compost in your garden or yard or you risk spreading unwanted plants throughout your landscape.
According to the Conservation Notes of the New England Wild Flower Society, you should put herbaceous invasive plant debris in a black plastic trash bag and set it in the sun to cook for about 30 days. Set woody plant material on an asphalt surface and allow it to dry out for about 30 days. After the month is over, the plant pieces are no longer viable and you can toss them in your garbage can in good conscience.
Nonchemical Control Techniques
Mechanical and manual control methods are great options for controlling young plants, single plants and small patches of multiple invasive plants. These methods won't have much effect on the environment and require only the most basic gardening tools to perform. Although you can use nonchemical control methods at any time, it's best to handpull, cut, grub or mow in the spring before the plants go to seed.
Repeatedly yanking out plants eventually kills invasive ground covers by exhausting the energy stored in the roots. Handpulling works best on plants that sprout from seed, including:
Wait until after a rain shower or water the area beforehand because it's easier to remove entire plants and their root systems from moist soils. You must extract every single piece of the roots because many invasives sprout into new plants from bits left in the soil. Inspect the area regularly for several years to see if seeding or resprouting occurs. Handpull and dispose of any new growth.
Some invasive plant species, including English ivy, can cause skin irritation.. Before handpulling plants, cover up exposed skin by wearing a long-sleeved shirt, long pants, close-toed shoes and sturdy gloves.
Cutting and Mowing
Repeatedly cutting or mowing invasive plants down to the ground interrupts the photosynthesis process, which weakens plants and eventually kills them by forcing them to use up all of their energy regrowing. These techniques take about two years to completely kill off unwanted plants.
Mow on the lowest possible blade setting or cut the vines at the soil line using garden shears or loppers. Keep an eye on treated area and cut down any new regrowth as it occurs. For optimal results, the folks at Gardens Alive recommend cutting plants once a week early in the growing season.
Some invasive plants spread contagious plant diseases. English ivy, for example, often harbors bacterial leaf scorch pathogens (Xylella fastidiosa) that can infect various native tree species. After treating invasive plants, play it safe and wipe off tools or mower blades with a solution containing equal parts 70-percent isopropyl alcohol and water
If cutting, mowing or handpulling don't get those pesky ground covers under control, consider digging them up. Regularly grubbing invasive plants eventually kills them by exhausting their energy sources. You'll likely have to repeat this process for about three years to get every bit of the plant gone.
Grubbing is a viable option for ground covers with really shallow roots, such as English ivy, as well as those that sprout from bulbs, including lesser celandine (Ranunculus ficaria, USDA zones 4 through 8) and Italian arum (Arum italicum, USDA zones 6 through 9).
Start the grubbing process by cutting off most of the foliage. Then push a digging tool, such as a gardening spade, fork or hoe, into the soil 4 to 6 inches beneath the plant and grub it up. Remove as much of the root system as possible without injuring the roots of nearby desirable plants. Roots and bulbs can resprout from even a little piece left in the soil, so dig down a few more inches and sift through the soil to make sure you get all of the little plant bits. Watch for stragglers and dig them up if they appear.
Mulching and Smothering
Mulching and smothering kills ground covering invaders by blocking out the sunlight needed to sprout and grow. Use thick layers of mulch to discourage small patches of unwanted plants. The Plant Conservation Alliance recommends using about 3 inches of an organic mulching material, such as wood chips, hay or grass clippings. The material must sit for at least two years, so keep adding more mulch to keep the layer at its initial thickness. Handpull any invasive seedlings that manage to pop up through the mulch.
Placing a layer of cardboard beneath the mulching material more effectively kills dense patches of ground cover. The North Carolina Botanical Garden suggests first cutting the vegetation down to ground level and then laying pieces of cardboard directly on top of the cut plants, overlapping the edges by a few inches so there's no little cracks for the plants to poke through. Cover the cardboard with organic mulching material and keep replenishing the material to keep it at its original thickness for at least two years.
For further information, please see "How to Kill Invasive Ground Cover Without Killing Everything Else."