5 Tips for Effective Weed Control

1. LET SLEEPING WEEDS LIE

Kill weeds at their roots but leave the soil—and dormant weed seeds—largely undisturbed. 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

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.

2. MULCH, MULCH, MULCH

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.

4. LOP OFF THEIR HEADS

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

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 didymaand cvs., USDA Hardiness Zones 4–9) and phloxes (Phlox paniculataand cvs., Zones 4–8).