Get Them Before They Start
Weeds compete with garden plants for nutrients, space, and sunlight. Weeds can make your otherwise tidy organic garden appear scraggly, and weeds harbor insect pests that carry diseases. The best way to control weeds without chemical herbicides is to prevent them from establishing themselves in your garden.
Adding a 3-inch layer of organic mulch is one of the best methods you can use to prevent weeds. Mulch prevents sunlight from reaching weed seeds, preventing them from germinating. Mulch retains moisture in the soil and keeps it from compacting, so that you can easily pull young weeds as they sprout.
You can choose bagged wood chips or shredded bark for your garden mulch, but compost makes excellent mulch. If you use compost or other finely textured mulch like grass clippings, replace it as frequently as once a month, as it breaks down quickly.
If you’re preparing to dig or till a new plot of exposed earth, devote a day to removing as many weeds as possible first. Many perennial weeds, like bindweed and thistle, spread by means of rhizomes or creeping stems. If you leave root segments behind, your tiller could distribute these viable plant parts throughout your garden, multiplying your weed problem a hundredfold.
Solarize Your Soil
You can make the greenhouse effect work for you by baking weeds and their seeds in situ, before you plant a barren plot. In the summer, cut all existing weeds to ground level.
Water the area thoroughly, and lay a sheet of clear plastic over the entire plot. Old shower curtain liners work well for this chore. Pin the plastic down with metal u-shaped stakes, so the wind doesn’t move the plastic sheets. If you use a single large sheet, weigh the center portion down with rocks to prevent cooling air pockets from forming.
After 8-10 weeks, the sun’s radiant energy will have sufficiently raised the temperature of the soil so that all weeds and seeds are no longer viable. As an added benefit, solarization kills many soil-borne diseases and pests. Your organic plot is now ready for a fall planting of cool weather vegetables.
SOURCE: University of California Cooperative Extension