Vegetable Seed Saving Handbook
To grow the healthiest, most vigorous plants, you must start with healthy, robust seeds.
Important characteristics of healthy seeds include:
All these characteristics affect each other—none stands alone. Each is a different way of measuring a seed's ability to survive and grow under normal conditions.
Viability refers to the germination rate, which is the percentage of a batch of seeds that germinates under ideal conditions. Vigor refers to the strength of growth of seeds once they have sprouted.
Viability and vigor are not separable—seeds which will sprout under ideal conditions must have enough vigor to emerge from the soil, or they cannot be considered viable under field conditions.
Size and maturity are also important, and inseparable from viability and vigor. The relative size and maturity of seeds relates directly to their survivability when planted—for highest viability and vigor, seeds must be large and fully mature. Large, mature seeds have more stored food to nourish the seeds once they have sprouted, and produce strong, vigorous seedlings which have a better chance of surviving and thriving under field conditions.
It is best to allow seeds to ripen to full maturity before they are harvested—mature seeds have higher germination and survival rates than seeds harvested at an immature stage. This is because of natural metabolic and cellular changes the seeds undergo as they mature, in preparation for dormancy.
The health of your seeds begins with the plants that produce them. Seed producing plants should be robust and disease-free. Strong, healthy plants produce healthy seeds and seedlings that are larger, more-viable and more-vigorous than seedlings produced by weak, diseased, drought-stressed or chronically-hungry plants. Small or misshapen seeds are shorter-lived under storage conditions than larger, better-formed seeds.
Small seeds contain less stored food to help them emerge from the soil and produce healthy seedlings. Although small seeds may show as high an initial germination rate as larger seeds under ideal conditions, they may lack the strength to emerge from the soil—particularly under less-than-ideal field conditions.
Sometimes plants are deliberately stressed early in their lives for the purpose of accelerating 'natural' selection. However, these stresses should be removed as much as possible as flowering time approaches in order to allow healthy seeds to form and develop.
In an extreme case you might even stress your plants to the point where even the well adapted ones make small, starved seeds (i.e., for faster results). In this case plan on treating the seeds more carefully during planting and germination, and replant them every year as both their viability (ability to survive storage and germinate) and their vigor (ability to survive after germination) will be compromised.
See Breeding New Varieties in this handbook for more on creating new varieties better adapted to your own gardening style, conditions or goals. Or—for a really thorough treatment of the subject—get Carol Deppe's book Breed Your Own Vegetable Varieties: The Gardener's & Farmer's Guide to Plant Breeding & Seed Saving.
Parent plants' health is not only important to the health of the seeds they produce, but can affect succeeding generations as well. Diseased plants pass disease pathogens to new plants through their seeds (see Treating Seeds for Viability and Disease Control).
Do not allow diseased plants to produce seeds; remove them from the growing area (and dispose of them by hot-composting or burning) so they don't pass their diseases on to their seeds or infect healthy plants.
The period of time when your plants are first beginning to flower is especially important to final seed viability. Plants should be strong, healthy and minimally stressed during early seed formation and development. Give seed-producing plants plenty of water, light and fertilizer early in their lives, so that they are strong and healthy when flowering commences.
Sufficient moisture at flowering time is particularly important to successful pollen development and flower set. Too little water during flower initiation and early seed development lowers seed yields, and can even hurt the health and vigor of your finished seeds and seedlings.
Conversely, though, dry conditions are preferable during the latter stages of seed maturation, when seeds have formed and are drying in preparation for dormancy (see Seed Maturation, below).
During seed maturation, warm (80º to 95ºF), dry conditions are most favorable to the final vigor, viability and storage life of your finished seeds (see note on seed initiation, above).
Wetting mature seeds slows their natural process of preparing for dormancy, extending the time during which their stored food reserves must be used for respiration. This lowers the seeds' final dry weight and shortens their storage life.
Repeated wetting and drying of mature seeds on the plant delays dormancy excessively, and can also damage seeds due to alternate swelling and shrinking of seed tissues. If they are left on the plant during rainy periods, seeds may even mold or mildew in their pods or husks. For these reasons, it is best to harvest your seeds and bring them inside for final drying as soon as they are fully mature and dry—especially if rains threaten (see Harvesting and Cleaning Seeds).
Biennial plants—such as collards, kale and chard for example—grow to maturity during one year, and then produce seeds early in their second year of growth. In areas where winters are mild, collecting seeds from biennial plants is not a problem. In colder northern climes, however, biennial plants may need some winter protection in order to survive harsh winters and produce seeds.
A variety of means can be used to assist biennial plants in making it through harsh winters. In intermediate areas, biennials can be grown in cold frames (unheated, plastic- or glass-covered enclosures) that offer protection against the harshest weather. Greenhouses can also be used, though greenhouse space is usually limited and most biennials need exposure to a period of freezing weather in winter to properly mature. A thick mulch applied after plants freeze back will probably suffice in all but the most extreme winter climates.
Another way to over-winter biennial plants in extreme climates is to dig them when extremely cold weather begins, and 'heel them in' over winter in damp sand or peat. Many biennial plants—since they are typically accustomed to becoming dormant over winter—will keep safely during the coldest months in this way.
Dig plants to be heeled in with an adequate root ball, and remove all but the smallest leaves and the finer branches to keep moisture loss to a minimum. Then bury the plants in moist sand, peat moss, sawdust or other relatively inert material, leaving just the crowns of the plants exposed (since the crowns are likely to rot if left buried). A tent of plastic sheeting will help protect the crowns against drying out during their storage.
Keep the container with the heeled-in plants somewhere temperatures will hover around freezing (a little freezing is acceptable for hardy plants). Keep the stored plants from hard freezes or from becoming dry or warm (if they get too warm they'll resprout prematurely).
When early spring comes and temperatures are likely to stay above 28º F or so, remove the plants from their storage places and plant them in containers. Then store the newly replanted plants in a protected spot to harden off (become accustomed to outdoor conditions) for two or three weeks before planting in the garden. If you prefer to plant the over-wintered plants directly in the garden where they will grow, it is a good idea to provide some protection from wind and full sun for at least a couple weeks. This gives the tender plants a chance to establish new roots and leaves before being exposed to harsh outdoor conditions.
All the above having been said, use your own experience as a final guide. If you've had biennial plants (such as carrots or cabbages, broccoli, etc.) over-winter and flower in your garden, then all you may need for safe over-wintering is a little extra mulch. Most biennial plants will over-winter reasonably well in at least the southern half of the U.S. If you live in the northern half of the U.S. or at high altitude, use your own experience (or experiment!) to determine the level of protection your biennial plants will need to over-winter successfully.
Reprinted from Vegetable Seed Savers Handbook, Jack Rowe 1998, howtosaveseeds.com