If you choose one variety of pea or potato or any other vegetable, and sow the seed or plants all on the same day, the whole lot will be ready for eating roughly during the same week a few months later, thus giving you no peas throughout the year except for two weeks in July, when there is a glut. Successional sowing avoids this ‘famine- and-glut’ situation.
There are two ways of spreading a crop over a longer period of time.
The first is successional sowing proper, i.e. by sowing part of the crop at intervals throughout the growing season: if you plan to grow four rows of peas, you sow one row at the appropriate time, wait until the seedlings are showing through the ground a week or ten days later and then sow the second row, after ten days the third and soon. This not only spreads the crop but if you are attacked by drought, or pigeons, or disease, you may lose one or even two of your sowings, but you will be very unlucky indeed if you lose all four.
The second method is to vary the variety so that you have early, mid-season and late varieties. Thus early peas should he ready about ten or twelve weeks after sowing, while mid-season peas need twelve or fourteen weeks. You therefore sow earlies in March/April and the main crop in May/June, and are sure of peas from mid June until late August or September.