Cross-pollination is when one plant pollinates another plant of a different variety. This can only happen within varieties, not species; for instance, a zucchini will not cross with a watermelon, but it can cross with a pumpkin. How readily this occurs depends on whether the plant is primarily or entirely self-pollinating, or if it needs to cross with others in order to set fruit. Self-pollinators, such as tomatoes, peas, and eggplant, do not readily cross on their own, while many others require the assistance of insects or the wind to pollinate. If they are planted near others of the same species, they are easily fertilized with pollen from a different variety. While this cross will not affect the fruit that is produced (except in one instance: corn), it will affect the seeds. Seeds from vegetables that have been cross-pollinated are no longer "pure", or true to type, which is vital for saving heirloom seeds. If you wish to return seed to the Seed Library, please take cross-pollination possibility into account; we cannot accept seeds which may not be pure. Additionally, plants require a certain population size to produce good seed, as seeds from too small a population may suffer from lack of genetic diversity. Required population size can range from as few as 5 plants, or as many as 200, so please consider this aspect as well.
A Guide to Isolation Distances
How to Plan for Population Sizes in Seed Saving
Garden Planning for Seed Saving
5 Tips for Planning Your Seed Garden
Healthy plants. Save seed from your best plants. Strong, healthy plants are most likely to produce good seed and pass on good traits to the next generation.
Genetic diversity. If the population size of a particular variety is too small, there may be too little genetic diversity for the plants to produce good seeds (species that are mostly or entirely self-pollinating, such as peas, require fewer plants to maintain genetic diversity than out-breeding types, such as spinach). In general, the more plants the better, but good seed can be obtained from only a few plants in some species.
Give plants some space. Some plants, such as peas and tomatoes, are largely or entirely self-pollinating, which means they do not readily cross with other related species. Others, such as melons and squash, are pollinated by insects or by the wind, so they easily cross with other plants of the genus. The fruits the plants produce will be true to type no matter what, but if they cross-pollinate, their seeds will grow into hybrid varieties. While this can make for some interesting experiments, it is undesirable from a seed preservation perspective. Cross-pollination can be avoided by planting different crossing types far enough apart, or simply by planting only one member of a cross-pollinating genus in your garden. If you believe some of your plants had the opportunity to cross-pollinate, please do not donate these seeds.
Start with easy plants. Peas, beans, lettuce, tomatoes are self-pollinating plants and their seed is easy to save for the novice gardener and seed-saver. If you have not saved seed before, these are excellent plants to start with.
Know when your seeds are ready. Not all seeds are ready at the same time as the fruit. Vegetables such as snow peas, summer squash and cucumbers are eaten when the seeds are small and immature. If you want to save seeds from these plants, leave some of the fruit on the plants to allow the seeds to mature (choose some of the best, healthiest-looking fruits for the best seeds!).
Know how to harvest seeds. Harvesting some types of seed, such as peas or corn, is as easy as picking the dry fruits off the plant and packaging up the seeds. Other types, such as tomatoes, require a few steps to save good seed. The process is not difficult, but it should be followed carefully to ensure viable seeds.
Know how to store seeds. Ensure that seeds are fully dry before packing them up, as residual moisture can harm them. Store prepared seeds in sealed containers (such as airtight plastic containers or freezer bags) and keep them in a cool, dark, dry place. Be very careful to keep them away from any moisture, since any water may cause them to rot or to germinate prematurely.
Run a germination test. This test allows you to find out how many of your seeds are viable for future growing. Non-viable seeds may be caused by a weak or diseased source plant, improper saving or storage techniques, or age. It’s important to test your seeds to ensure that you do not return non-viable seeds to the seed library. A germination rate of 70% or higher is suitable for returns.
The Complete Guide to Saving Seeds: 322 Vegetables, Herbs, Flowers, Fruits, Trees and Shrubs: A full-color resource explains how to gather, clean, and store seeds for three hundred different kinds of vegetables, fruits, herbs, flowers, trees, and shrubs, as well as how to propagate and care for new seedlings. Available in print at the Macdonald Campus Library (call number SB118.3 G68 2011).
Seed to Seed: Seed Saving and Growing Techniques for Vegetable Gardeners: This is a complete seed saving guide that describes specific techniques for saving the seeds of 160 different vegetables.. Available in print at the Macdonald Campus Library (call number SB324.75 A8 2002).
The Manual of Seed Saving: Harvesting, Storing and Sowing Techniques for Vegetables, Herbs and Fruits: This authoritative guide brings together the experience of experts in the field who have found, through careful trialing, how to reliably maximize seed quality and yield for more than 100 crop plants. Clear information on such critical issues as pollination, isolation distances, cultivation, harvest, storage, and pests and diseases is provided. Available in print at the Macdonald Campus Library (call number SB324.75 H4513 2013).
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