Peas are among the easiest to grow seeds from. They are annual and self-fertilizing. There is little risk of cross-fertilization and different sorts can grow close together. They are easy to thresh and show a marked improvement after a year, as long as only the very best plants are allowed to yield seed. A security distance of 500 m is needed if the seed has to be absolutely pure for each sort.
Grow the peas as usual and remove all deviant plants, the unusually small ones, the ones with hairy leaves, when they are discoloured, when late blooming, if they are victims of weakness and sickness. Also make sure to remove deviant pods when ripe. Peas do have a tendency to degenerate genetically. The more careful the thinning, the better the seeds next year. The first sowing, when the seeds ripen during late summer, yields the best seeds.
The seeds are ripe when they rattle inside the pod. Usually the whole plants are pulled out and allowed to continue ripening in or outdoors. The seeds don"™t ripen all at once and it is advantageous, in a smaller plot, to pick the pods one by one as they ripen. That also diminishes the risk that the peas begin germinating inside the pods during wet autumns.
Thresh, clean and store the peas in the same way as the beans.