If you're growing any type of plant, summer or winter squash, cucumbers, watermelon or cantaloupe, you can plant them under black plastic. We put the plastic down, anchor it with wires all the way around the edges (about every 2') to keep it from blowing, then cut holes in it to place the seeds or plants (3' apart for tomatoes squash, cucumbers or cantaloupe, 1' between peppers, eggplant, and cabbage), and hold the plastic down at each plant with wires (we take about 6-7" lengths and bend them into the shape of a long staple). It not only keeps out weeds, but it also holds in moisture and heat. Make sure your holes are big enough (about 3-4") that the seeds don't start growing under the plastic, though.
Have about a 50' x 50' area planted under black plastic with most of these so far.