Consider size, harvest time and other characteristics. Always harvest mature seed. For example, cucumber seeds at the eating stage are not ripe and will not germinate if saved. You must allow the fruit and seed to fully mature. Because seed set reduces the vigor of the plant and discourages further fruit production, wait until near the end of the season to save fruit for seed.
Seeds are mature or ripe when flowers are faded and dry or have puffy tops.
Plants with pods, like beans, are ready when the pods are brown and dry. When seeds are ripe they usually turn from white to cream colored or light brown to dark brown. Collect the seed or fruits when most of the seed is ripe. Do not wait for everything to mature because you may lose most of the seed to birds or animals. Beans, peas, onions, carrots, corn, most flowers and herb seeds are prepared by a dry method.