Seed Storage

Preparing Your Seeds for Storage is Important

How you prepare and store your seeds can be as important to their eventual viability as how they were grown. Seeds must be carefully dried and then stored under the proper conditions in order to give them the best chances of germinating and producing healthy plants. Luckily, all the needs of seeds are easily provided once you are aware of their requirements.


Cold Stratification

Most seeds in nature that have their origins in temperate climates require a period of cold storage known as stratification before they will germinate. Mother nature has developed this requirement to prevent fallen seeds at the end of a growing season from germinating only to die off in the coming winter freeze. Because of the many different varieties of both cannabis and poppy found throughout the world, some do better with a period of stratification while others can be planted as soon as they are mature. Store your harvested seeds in the refrigerator below 35° for around 2 months prior to planting to insure successful germination if you are unsure of your strains origins.

For purposes of storage, there are basically two types of seed: ‘desiccation-tolerant’ and ‘desiccation-intolerant’. Most of the garden plants with which we are familiar produce desiccation-tolerant seeds, which means they can be safely dried for long-term storage. Exceptions include many aquatic plants, large-seeded plants, and some trees (such as oaks and buckeyes), many of which produce desiccation-intolerant seeds and will die if allowed to dry.

Preparing Desiccation-Tolerant Seeds for Storage (Cannabis & Poppies)

During ripening and drying, desiccation-tolerant seeds prepare for dormancy by greatly slowing or ceasing most physiological processes, and by converting food reserves from sugars to more stable fats and starches. After they have prepared for dormancy, and unlike desiccation-intolerant seeds, desiccation-tolerant seeds can be safely dried and stored for long periods of time without significant loss of viability (many years in some cases). Some desiccation-tolerant seeds even require drying to complete the ripening and dormancy process before they will germinate.

How desiccation-tolerant seeds are dried and stored is very important to maintaining their viability and vigor over the long term. Drying should be gradual and thorough, and desiccants used when drying seeds in air above 30% relative humidity or so. During storage, seeds must be kept at appropriate temperature and moisture levels for greatest longevity.

Even under ideal conditions, long-term storage lowers viability percentages (since some seeds die) and also lowers the vigor of seedlings produced by the stored seeds. Further, as length of time in storage increases, the number and percentage of seedlings with damaging mutations or tissue degeneration also increases. Roots in particular are adversely affected by long-term storage. The more frequently a batch of seeds is regrown (and therefore the shorter the storage times), the better will be the overall health of the plant populations produced.

Desiccation-tolerant seeds should be slowly dried in a shady spot. Spread seeds one or two thick in an airy, dry location—such as an air-conditioned environment or other place where relative humidity stays between 20% and 40%—for two or more weeks. Large seeds must be dried longer than smaller seeds. When dry, corn and beans will shatter when hit with a hammer, squash seeds will break instead of bending. Seeds which pass this test are dry enough for safe short-term storage.

Cannabis Seeds
Poppy Seeds
Silica Gel Seed Storage

Using Silica Gels For Final Drying

Seeds air-dried during humid weather require additional drying with desiccants such as silica gel before final storage (but don’t use heat!). Most seeds benefit from drying with silica gel if they are to be stored for very long. The longest storage life for desiccation-tolerant seeds is achieved by drying them to between 5% and 7% moisture content (by weight) and then storing them at several degrees below freezing. As storage temperature rises above freezing or moisture content rises above 5 to 7%, longevity in storage goes down and the incidence of mutation rises. Seeds dried to a low moisture content with silica gel and then stored in a freezer can usually retain viability for many years.

To use silica gels for drying seeds, place equal weights of dry silica gel and seeds to be dried in a well-sealed jar for 7 to 8 days. Then transfer the dried seeds quickly into airtight storage jars and place in a freezer, refrigerator or other cool, dark place.

Since desiccation-tolerant seeds stop almost all metabolic activity as they mature and dry, they can be stored for months or even years with only minor loss of viability and vigor. Desiccation-tolerant seeds which show high germination percentages when fresh—if properly dried and stored in a freezer—can typically retain their viability for years.

Seeds with low initial germination rates will begin to lose viability fairly quickly, however, even under ideal storage conditions. Seed lots with a low initial germination rate should be regrown as soon as possible. If a batch of seeds with poor germination is grown out and a healthy batch with good germination produced from them, the healthy batch can then be dried, frozen and stored for long periods successfully.

Avoiding Problems With Stored Seeds

Mold and Mildew: A common problem with stored seeds is mold or mildew resulting from incomplete drying before storage. Dry your seeds thoroughly before storing them (though drying them to 0% moisture will of course cause their death). If seeds sweat on insides of jars during storage, they are too wet and must be dried further in order to store successfully. At this point the use of a desiccant is a good idea. Don’t tarry, because damp seeds will mildew quickly.

Temperature and Moisture Fluctuations: Fluctuation in temperature or moisture levels of stored seeds lowers the seeds’ longevity significantly, causing loss of viability and vigor or even seed death. Rapid moisture fluctuations are particularly damaging to seeds. High moisture or temperatures encourage mutation of seed tissues—especially in root tips, which remain more active than other seed tissues. Cellular mutations affecting metabolism or root tissue structure are a common cause of seed failure upon germination. Dry your seeds properly before placing them in cold storage. Keep your stored seeds at a constant temperature if possible and remove them from storage as seldom and as few times as possible. When seeds are removed from cold storage in order to retrieve samples, allow the entire container to come slowly to room temperature before opening the seal. This will help prevent condensation of atmospheric moisture onto the cold seeds which might otherwise occur.

Insects: Another common problem with stored seeds is infestation by weevils or other insects. In fact, it is best to assume that some insects are present in any sample of seeds. Seeds kept in frozen storage are safe from insect damage, since—though insects may survive the freezing—they will be rendered inactive while frozen by the low temperature. Even if your seeds will be stored frozen, however, it doesn’t hurt to take precautionary measures against insects. Insect infestations may be guarded against by the addition of a little diatomaceous earth (D.E.—available at organic gardening stores) to the stored seeds in their jars. Add just enough D.E. to cover the surfaces of the seeds (add a few pinches to the seeds in a bowl and gently stir to thoroughly cover each seed). Adding D.E. to jars of stored seeds helps insure the long-term safety of your seed stocks and is an inexpensive, safe, non-toxic and wise precaution.

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