Although the glass is usually half full in my world view, and certainly in my garden view, I admit to feeling defeated this week. During the muggy weather, I could only stand to work outside very early in the morning, and I had to tackle a large swath of garlic mustard, with some bedstraw, before the seeds blew. I scooted along on my bottom, pulling with both hands, determined to leave no flower heads behind.
Garlic mustard is a noxious weed (listed as invasive in New York State) that continues to develop viable seeds even after it is uprooted, so you shouldn’t let the pulled plants remain on the ground. Doing the work, I was especially irked at myself because I should have caught the first few plants that appeared during the last three years. And this season I should have gone after them all much sooner than I did. I also ran out of time to finish the task, as my work – and some black fly bites around my eyes – forced me back inside.
Is there any easier way to remove large patches of weeds? What else could I have done, and what if the area had been even larger? These questions come up often, and I’m not the only gardener who gets overwhelmed.
Plastic, paper, carpet
One straightforward way to stop nasty plants, for a while at least, is to smother them. For a large area, spread sheets of heavy plastic (the thicker the better) over the weedy areas. Look for 10-by-20 or 20-by-40 sheets and cut to size. Some gardeners even use carpet, and I have done so.
For appearance, cover the plastic or carpet with mulch. I have stopped Japanese knotweed and goutweed by covering vast swaths of them, extending the coverage 10 feet beyond the visible weeds. Watch for new weeds poking up beyond the sheets, and keep digging them out. Eventually some weeds such as cinquefoil or creeping Charlie will creep on top of the plastic and root in the mulch, so you’ll have to catch them as they take hold. It’s quite satisfying to rip the sheets up after a couple of years, and see all the dead weeds beneath and growing into them.
In smaller spaces, such as the perennial garden, blocking weeds is more complicated. First pull any weeds before they go to seed, whether they are annual or perennial weeds. A piece of dandelion root will regrow, but that’s just one plant; it’s more important to stop that puffy flower head from making hundreds of babies. I pull the weeds, spread compost or leaves to enrich the soil, and then put down thick newspaper sections topped by heavy weight garbage bags or cut plastic sheets around the perennials and shrubs. I then mulch with shredded bark or pine needles.
Ground covers and buckwheat
Some plants can outcompete weeds, with a little support from us. If you have a hill or bank you want to weed and cover – not the place for lawn – consider ground-covering perennials or creeping vines. Cornell University produced a study showing spreading perennials that block weeds, including ladies’ mantle, Sedum ‘John Creech’, butterfly weed, catmint and a low-growing aster.
Many farmers spread cover crops such as alfalfa, oats and grain combinations, and some of their methods may apply to your large weedy tract. Buckwheat is an attractive, easy grower, loved by pollinators, and it blocks weeds better than any other seeded crop to my knowledge.
Herbicides are products that kill plants or inhibit plant growth in several different ways, some by direct contact and others systemically. Only you can decide if you are going to use any herbicide products, but if you do, you must read and heed the label – by law – and you should clearly understand how the product works and whether it applies to your problem.
So many people simply buy something labeled “weed killer,” with no clue about correct application, timing or the targeted plants. There are harmful environmental and health consequences of using some products, especially at the wrong time, in the wrong amounts, on the wrong target plants. Wrong use also wastes time and money. I do not use them. Here are some basic answers to some common questions:
Can I use a pre-emergent weed killer?
Pre-emergent herbicides stop weeds like dandelions from growing, but timing is everything. These products must be applied before the weeds start to grow (often sometime in March and mid-September). Read labels; ask experts.
Is there an organic herbicide?
Even organic lawn care experts disagree sometimes, but products containing corn gluten meal, such as organic Preen, appear to inhibit weed growth effectively, without harmful effects. Besides, they contain nitrogen so they are also an organic fertilizer that can’t hurt. Organic lawn care relies on the premise that a healthy, thick lawn, cared for properly, beats out most weeds – but it’s a process, not a quick-kill approach. Consult an expert.
What about Roundup?
Products like this kill plants through leaf contact, and must be applied on large areas of leaves, so let the goutweed, creeping Charlie or poison ivy grow for a couple of months, and then spray them or brush them with the product, more than once. Read the label. Be extremely careful; wind drift can kill nearby plants. Such products are one of the only effective tools for managing powerful, invasive plants – a tough dilemma when we prefer organic methods.
Weeds are part of gardening, and we can usually stay ahead of them. Don’t be discouraged. When you can’t fight any more, it may be time to renovate the whole garden, and call in professional CNLPs to take on the job.
Sally Cunningham is a garden writer, lecturer and consultant