A thick layer of mulch keeps light from reaching weeds. "Without adequate light, the plants don't produce enough chlorophyll to enable further growth. Most of these plants sicken and die before you even notice them," writes Miranda Smith in Rodale's Chemical Free Yard & Garden. "The few plants that do manage to stick their leaves into the light will be shallowly rooted and very easy to pull."
Organic mulches—straw, grass clippings, leaves, shreddedbark—nourish the soil as they decompose. They are fairly effective weed barriers. For even better weed protection, use several sheets of newspaper, kraft paper (the paper used to make grocery bags) or cardboard under these mulches. In a 1992-93 study at the University of Vermont, a 6-inch layer of shredded newspaper applied at the beginning of one season allowed no more than 8 weeds per square yard to sprout for two summers. Without renewing the mulch layer, the newspaper controlled weeds for two seasons. Kraft paper and cardboard allow even less light to reach weeds and are even more impenetrable.
Annual weeds die when you sever the stems from the roots just below the soil surface. With a sharp hoe, you cut the weeds easily. Forget about the square-headed traditional garden hoe for this job—go for an oscillating or a swan neck hoe instead.
To hoe your garden without cultivating a backache, hold the hoe as you would a broom—that is, with your thumbs pointing up. Skim the sharp sides of the hoe blade through the top inch of the soil.
You can let the sun help you get rid of persistent weeds, if you're willing to leave the bed fallow for six weeks in the summer. Get started in late spring or early summer by pulling, hoeing or raking out as many weeds as you can from the garden bed. Then, moisten the soil and cover it with clear plastic, weighting or burying the edges. Leave the plastic in place for 6 weeks. When you remove the plastic, the sun will have cooked weeds that would otherwise have sprouted.
Read the Seven Samurai of Organic Weed Control.
Corn Gluten Meal
You can suppress the growth of weed seeds early in the season by spreading corn gluten meal over the area where they're growing. Corn gluten meal, a by-product of corn processing that's often used to feed livestock, inhibits the germination of seeds— bear in mind, once the weeds have gone beyond the sprout stage, corn gluten will not affect them. Also, corn gluten doesn't discriminate between seeds you want to sprout and those you don't want, so avoid using corn gluten meal where and when you've sown seeds. It works best in established lawns and perennial beds.
Here's the trick to comfortable, quick weed-pulling:
Put your hands in front of you, thumbs up and palms facing your body, one hand in front of the other. Now roll your hands, like kids do when singing "This old man goes rolling home."
Pinch your forefinger and thumb together as you reach the outermost edge of the imaginary circle your hands are tracing and move your arms to the side as you roll your hands.
With practice, you will be surprised by how quickly you clean up a row in the garden with this movement.
This is your most important long-range weapon against weeds. Mulch well, pull what you can, hoe where you have to and use a handy tool or two for a few minutes whenever you visit your garden. Do these things consistently for a few seasons, and you will slowly, but surely expel the invaders for good.