Seeds should not be harvested until fully ripe or mature. While this is true, it is equally important to be prompt in gathering the crop when the proper time has arrived. If sprouting or molding does not occur, the seeds will discolor if left too long on the stalk, and this is always objectionable when they are wanted for commercial purposes. Seeds are generally ripe when the pods or seed capsules turn yellow, or the fruits, as tomatoes and melons, lose their firmness.
Bright, sunny weather should be selected, if possible, for the harvesting of crops which require threshing. The plants should be thoroughly dried before threshing, and it is always better to select days of low humidity for this operation. Whatever the method, whether by flailing or by machines, the greatest care should be exercised to prevent breaking the seeds or the seed coats. Windmilling is necessary for further cleaning of the seed.
In securing clean seeds, vegetables such as tomatoes and melons must stand for some time in their juices to remove the mucilaginous covering. A common method is to throw the cut or broken specimens, or sometimes the pulp, into any convenient vessel, as a crock, tub or barrel, and stir daily until fermentation has loosened the covering about each seed. Then the operation may be completed by washing. To prevent the discoloring of seeds, the fermentative process should not be continued longer than necessary.
After fermentation, the seeds are separated from the pulp and the skin by washing as often as may be required to obtain clean seeds. The good seeds settle to the bottom of the vessel, while pulp, skin and light seeds rise to the top, and may be poured off. Three or four washings are usually sufficient. Sieves are often used in the process of separation by washing.
After windmilling or washing the seeds must be thoroughly cured before storing. They should be spread in thin layers in lofts, or in dry, well-ventilated places until thoroughly cured. It is an advantage to wash early in the morning of bright days to facilitate drying. Seeds must not be subjected to freezing temperatures before being cured, for this invariably impairs their germinating power.