Most common vegetables are annuals which grow from seed, then flower and produce fruit all in one season. Some vegetables such as tomatoes and peppers continue to produce fruit all summer and although they sometimes take a break in very hot temperatures, they will continue until frost kills them. Other vegetables, such as green beans and pea varieties, have a more limited life span and these peter out after a few weeks of harvest. Other vegetables like carrots are harvested by pulling the whole plant up. All these are the reasons that you continue to sow some vegetables from spring until mid summer to extend the harvest and this is termed succession planting.
Cool Weather Vegetables for Succession Planting: Peas, lettuce, carrots and potatoes are all examples of early spring vegetables that are sown as soon as the ground is free of winter cold. Plant a few seeds or seedlings of these varieties every couple of weeks until a week or two past your last frost date. Lettuce and peas need to mature before hot summer weather arrives and it takes from 45 to 60 days to do that depending on variety. For lettuce you can get a little extra harvest by planting some heat tolerant or long day length varieties as spring advances. Succession planting, but in reverse, is used from mid-summer so that the vegetables mature in cool fall weather. Just sow a few seeds each week from 10 weeks to about a month before your first expected fall frost.
Warm Weather Vegetables for Succession Planting: Beans and sweet corn are the most common summer vegetables for succession planting. From about a week after your last frost the first seeds can be sown. Continue to sow seeds every two weeks until about July 4 th and the seeds will grow and produce fruit until the first fall frosts. Check the number of days the variety takes to mature to ensure that your harvest is before the first expected fall frost.