Tips for Effective Weed Control

by Barbara Pleasant

Photo/Illustration: Michelle Gervais

If you were to track every hour spent in your garden, you would probably find that you do an inordinate amount of weeding. And while the first few weeks of tearing up these intruders can prove mildly satisfying, the chore soon wears thin. Even more maddening—you are just six simple strategies away from your garden not needing weeds anymore.
What’s that? A garden needs weeds? Weeds are nature’s healing remedy for sites that are in a wounded, plantless state, but weeds and gardeners have different ideas of what makes for a good recovery. Armed with a better understanding of weeds and the strategies outlined here, you can win every future skirmish, giving you more time to enjoy your well-groomed garden.

1. Let sleeping weeds lie

Kill weeds at their roots but leave the soil—and dormant weed seeds—largely undisturbed. Photo/Illustration: Brandi Spade

Every square inch of your garden contains weed seeds, but only those in the top inch or two of soil get enough light to trigger germination. Digging and cultivating brings hidden weed seeds to the surface, so assume weed seeds are there ready to erupt, like ants from an upset anthill, every time you open a patch of ground. Dig only when you need to and immediately salve the disturbed spot with plants or mulch. In lawns, minimize soil disturbance by using a sharp knife with a narrow blade to slice through the roots of dandelions and other lawn weeds to sever their feed source rather than digging them out. Keep in mind that weed seeds can remain dormant for a long, long time.

2. Mulch, mulch, mulch

Don’t give weeds the chance to see the light. Whether you choose wood chips, bark nuggets, straw, or even pine needles, keep the mulch coming to smother out weeds. Photo/Illustration: Michelle Gervais

Mulch benefits plants by keeping the soil cool and moist and depriving weeds of light. Organic mulches, in particular, can actually host crickets and carabid beetles, which seek out and devour thousands of weed seeds.
Some light passes through chunky mulches, and often you will discover—too late—that the mulch you used was laced with weed seeds. It’s important to replenish the mulch as needed to keep it about 2 inches deep (more than 3 inches deep can deprive soil of oxygen). In any case, you can set weeds way back by covering the soil’s surface with a light-blocking sheet of cardboard, newspaper, or biode­gradable fabric and then spreading prettier mulch over it.
If you choose to use this method on seldom-dug areas, such as the root zones of shrubs and trees, opt for tough landscape fabric for the light-blocking bottom sheet. There is a catch, however: As soon as enough organic matter accumulates on the landscape fabric, weed seeds dropped by birds or carried in on the wind will start to grow. For the bottom layer of fabric to be effective, these must be pulled before they sink their roots through and into the ground.

Monday: Kill weeds. Tuesday: Kill weeds...

If you’re a new gardener—or you’re working in a wild and weedy space—the first season will likely be a rough one. Commit (and stick) to a weeding schedule, and don’t take on more space than you can manage. If you have more weeds than you can handle, keep weedy areas mowed until you’re ready to conquer them.

3. Weed when the weeding’s good

Young weeds go down much easier than older ones, so make the most of good weeding conditions. Photo/Illustration: Michelle Gervais

The old saying “Pull when wet; hoe when dry” is wise advice when facing down weeds. After a drenching rain, stage a rewarding weeding session by equipping yourself with gloves, a sitting pad, and a trug or tarp for collecting the corpses. As you head out the door, slip an old table fork into your back pocket because there’s nothing better for twisting out tendrils of henbit or chickweed. When going after bigger thugs, use a fishtail weeder to pry up taprooted weeds, like dandelion or dock.
Under dry conditions, weeds sliced off just below the soil line promptly shrivel up and die, especially if your hoe has a sharp edge. In mulched beds, use an old steak knife to sever weeds from their roots, then patch any open spaces left in the mulch.

Heat is the key to composting weeds

Few experiences compare to the joy of watching weeds shrivel in the sun after a morning weeding session, but then what should you do with them? Their best resting place, of course, is a compost pile or bin, which is the end of the story if the weeds going in are free of seeds. In reality, however, a good half of the weeds you pull probably hold seeds. Separating the seedies from other weedies is impractical, so weed seeds in compost are customarily killed by raising the temperature in the heap.
Keep it hot. Running a hot heap calls for precise mixing and remixing of materials. Rather than struggle to heat up a heap that wants to run cold, I suggest waiting until a weedy heap reaches a nearly rotted state to set things right. From there, you can solarize small batches of moist compost in black plastic nursery liners that are enclosed in clear plastic bags and placed in the sun for two to three days.
Now you’re cooking. Easier than solarizing, plug in an old Crock-Pot outdoors, turn it to its lowest setting, and warm batches of compost while you sleep (three hours at 160°F kills most weed seeds).
Heat treating weedy compost destroys many of the microscopic life-forms that give compost its punch, so it’s a good idea to reprocess cooked compost for two to three weeks before using it in the garden. Place it in a plastic storage bin with a handful of earthworms borrowed from your garden and it will soon be laced with humic acids and other plant-pleasing compounds.

4. Lop off their heads

Chopping off weed heads feels good and you’ll reap short- and long-term benefits. Photo/Illustration: Brandi Spade

When you can’t remove weeds, the next best thing is to chop off their heads. With annual weeds, dead­heading buys you a few weeks of time before the weed “seed rain” begins. Cutting back the tops of perennial weeds, like bindweed, reduces reseeding and forces them to use up food reserves and exhaust their supply of root buds, thus limiting their spread.
You will need pruning loppers to take down towers of ragweed or poke, or you can step up to a string trimmer equipped with a blade attachment to cut prickly thistles or brambles down to nubs. No matter which method you choose, chopping down weeds before they go to seed will help keep them from spreading.

5. Mind the gaps between plants

Tightly planted beds leave no room for unwanted visitors. Photo/Illustration: Todd Meier

Close plant spacing chokes out emerging weeds by shading the soil between plants. You can prevent weed-friendly gaps from the get-go by designing with mass plantings or in drifts of closely spaced plants rather than with polka dots of widely scattered ones. You can usually shave off about 25 percent from the recommended spacing.
Most spacing recommendations, however, are based on the assumption that adjoining plants will barely touch when they reach mature size, so stick with the guidelines when working with plants that are prone to foliar diseases, such as bee balms (Monarda didyma and cvs., USDA Hardiness Zones 4–9) and phloxes (Phlox paniculata and cvs., Zones 4–8).

6. Water the plants you want, not the weeds you’ve got

Drip irrigation is the way to go for a quick way to water your plants and not your weeds. Watering by hand works, too, but it’s often tedious. Photo/Illustration: Steve Aitken

Put drought on your side by depriving weeds of water. Placing drip or soaker hoses beneath mulch efficiently irrigates plants while leaving nearby weeds thirsty. In most climates, depriving weeds of water reduces weed-seed germination by 50 to 70 percent. Watch out, though, for the appearance of deeply rooted perennial weeds, such as bindweed and nutsedge, in areas that are kept moist. They can take off in a flash when given the benefits of drip irrigation.
Beyond these strategies, enriching your soil with organic matter every chance you get can move your garden along down the weed-free path. Soil scientists aren’t sure how it works, but fewer weed seeds germinate in soil that contains fresh infusions of good compost or organic matter. One theory makes elegantly simple sense: When soil is healthy and well fed, weed seeds sense that they are out of a job and are less likely to appear.