From Just Food:

Did you ever wonder how your farmer has a supply of some vegetables all summer long? Or how they grow so much food on so little land? Farmers who practice small-scale sustainable agriculture use a method called succession planting to increase the amount of produce they can grow on their land.

There are four primary ways to do succession planting: 1) planting a second crop in the same space after the first crop is harvested; 2) planting one crop at staggered intervals so that it matures at different dates; 3) planting non-competing crops together in patterns; and 4) planting varieties of the same crop with different maturing dates at the same time. To use succession planting effectively farmers need to take into consideration a number of variables such as weather, the frost-free date in the Spring, the first-freeze date in the Fall, soil temperature, and insect and disease occurrence. All this allows you as a CSA member to receive your favorite vegetables such as lettuce, broccoli and beets, not just once, but throughout the season.