To control weeds in empty flower and vegetable beds that you will be replanting in fall, try "solarizing" the soil. By spreading a clear plastic sheet over the soil, you can trap the sun's heat there and cook weed seeds and seedlings. The process works best where daytime temperatures stay above 80° for four to eight weeks.
1. Till the soil, removing weeds, debris, and large clods.
2. Make a bed at least 2½ feet wide, carve a small ditch around the perimeter, and rake the bed level. Soak soil to a depth of 1 foot.
3. Cover soil with 1- to 4-mil clear plastic (use UV-resistant plastic if available). Stretch plastic tightly so it's in contact with soil, and bury the edges in the perimeter ditch. Leave plastic in place for four to eight weeks (but no longer, since that may harm beneficial soil organisms). Remove plastic and begin planting.