Hand-pulling, mowing, mulching, and other physical methods
Hand pulling or hoeing is your first line of defense against weeds, especially annual and biennial kinds. If you're diligent for several years about removing these before they set seed, their numbers will decline significantly.
Perennial weeds are harder to manage. Once they've passed the seedling stage, they develop rhizomes, bulbs, tubers, or extensive root systems that aid in reproduction. Pulling usually doesn't remove these underground structures completely, and the weeds can resprout from fragments left behind. It's best to dig these weeds, removing as much of the root system as you can ― a process you may need to repeat several times.
Don't leave pulled or hoed-out weeds lying on bare ground, since they may take root again. Leafy annual or biennial types that do not yet have flowers or seeds can safely be relegated to the compost pile, as can the top growth of perennial weeds (before seeding). But roots of perennials (dandelions and quack grass, for example) should be tossed in the trash rather than composted ― as should any weeds that have set seed.
HAND WEEDING. Pulling weeds by hand is time consuming, but it's also the safest way to eliminate weeds growing close to desirable plants without risking injury to the "good" plants' roots. Fortunately, various tools are available to make the job easier. A trowel or small cultivator helps loosen the soil around weeds; a dandelion weeder helps pop taprooted weeds from the ground. To get weeds out of cracks in pavement, use a screwdriver, weeding knife, or putty knife.
HOEING. A time-honored method of weeding both vegetable and ornamental gardens, hoeing also loosens the top layer of soil, improving water and air penetration. Garden centers and mail-order companies offer many sorts of hoes. Narrow, pointed ones are good for weeding around vegetables. A garden hoe with a sharp edge cuts off weeds at ground level; it's the best choice for open areas, such as the spaces between rows of vegetables. Various scuffle or oscillating hoes are especially useful for weeding under spreading plants.
CULTIVATING. For larger areas, such as orchards, vacant lots, roadsides, or plots intended for future garden use, rototilling or discing will do the job. These methods not only knock down the weeds but also incorporate them into the soil, where they decay to form humus. Some weeds may sprout again from the roots or crowns, so you may need to till several times.
MOWING. Rotary mowers and weed eaters are other good choices for weed control in larger areas. Both tools cut the weeds; weed eaters leave the severed tops behind, while mowers grind them up as they cut them. Of course, these methods do leave the weeds' roots and crowns behind to grow again.
FLAMERS. Powered by propane or a mixture of propane and butane, these devices are not meant to burn weeds. Instead, they heat them to the point that their cell walls burst. Though this damage is enough to kill many weeds, types with deep perennial roots usually regrow; eradicating these requires several treatments. Take care when using flamers around mulches, and never use them in dry, fire-prone areas.
GROUND COVERS. Sometimes called living mulches, ground covers are effective in preventing weed growth: like organic and inorganic mulches, they keep sunlight from reaching weeds and their seeds. For the first few seasons after you plant a ground cover, you'll usually have to do some hand weeding or apply a mulch, but as the cover grows and spreads to form a tight carpet, weed growth is much reduced.
SMOTHERING. Smothering effectively kills weeds in areas earmarked for future planting. After mowing or cutting off the top growth, lay down a mulch of heavy cardboard, newspaper (in a layer at least three dozen sheets thick), or black plastic. Overlap these materials so weeds can't grow through the cracks. Anchor the covering in place with a layer of bark chips or other organic mulch. Leave this smothering mulch in place for at least a full growing season; allow a year or more for tough weeds.
SOIL SOLARIZATION. Soil solarization takes advantage of the sun's heat, trapped under clear plastic sheeting, to control many kinds of weed seeds as well as harmful fungi, bacteria, and some nematodes.
MULCHES. Like any other seeds, weed seeds require sunlight, warmth, and moisture to germinate and grow. Mulches block light from the soil below, thus preventing the seedlings from becoming established. They also help keep soil moist and modulate its temperature. You can choose from organic or inorganic mulches.
• Chopped leaves. Whole leaves tend to mat, so chop them with a shredder or lawn mower. Compost them in piles over winter, then apply in a 3- to 4-inch-thick layer in spring.
• Compost. An ideal mulch, assuming your compost pile heats up enough to kill any weed seeds it may contain. Apply in a 2- to 3-inch-thick layer.
• Grass clippings. Apply in thin layers, building up to a layer 2 to 3 inches thick; let each layer of clippings dry before adding another, since a thick layer of fresh clippings will mat down and turn slimy. Or spread the clippings on the driveway to dry before applying.
• Pine needles. Pine needles acidify the soil and are best used around acid-loving plants such as rhododendrons and azaleas. Apply in a 2- to 4-inch-thick layer.
• Shredded bark, ground bark, bark chips, wood chips. Apply in a 2- to 4-inch-thick layer. Thicker layers provide longer-lasting weed control.
Inorganic mulches include gravel and stones, black plastic, and landscape fabrics.
• Gravel, river rock, and other kinds of stones. These materials make permanent mulches that can suppress weeds effectively ― as long as you install them over weed-free soil to begin with. Many gardeners place landscape fabric under gravel.
• Black plastic. This is especially helpful in the vegetable garden. Besides effectively preventing weed growth, it warms the soil early in the season, speeding the growth of heat-loving plants like melons. Place the plastic, available in rolls, over the soil, then cut slits in it where you want to plant seeds or transplants. Remove the plastic at the end of the growing season, since by this time it will usually have degraded too much to use again.
• Landscape fabrics. Sold in nurseries and garden supply centers, landscape fabrics are made of woven polypropylene, spun-bonded polyethylene, or a combination of other synthetic materials. Unlike plastic sheeting, they are porous, allowing air, water, and dissolved nutrients to reach the soil. Density and porosity vary with the manufacturer; the denser fabrics are better for suppressing weeds.
Landscape fabrics are available in various widths and lengths. They're best used in permanent plantings around trees and shrubs; they aren't really suited for beds of vegetables or annuals, where you change plants often. You can install them around existing plants or cut slits in them to accommodate new ones.
Before you install the fabric, eliminate weeds. Unroll the fabric and estimate where to cut it. Use sharp scissors to cut slits (X-shaped slits work best), then carefully fit the fabric over or around the plants. Overlap seams by at least 3 inches to avoid gaps through which weeds can grow. To anchor the outer edges of the fabric to the soil, use plastic pegs, nails, or heavy wire staples.
After installation, cover the fabric with 2 to 3 inches of a weed-free organic mulch such as bark chips or with a thinner layer of pea gravel or smooth river rocks. The mulch protects the fabric from ultraviolet degradation and improves its appearance.