I spent part of today talking to a retire Professor from the California University system. His expertise is in plants, particularly tomato plants. The subject we discussed was the long-term storage of plant seeds. Based on his many years of experience he said that the best method is to store seeds in a paper sack in the refrigerator. In his opinion, the preferred temperature to store seeds is 50 degrees. For practical purposes, a refrigerator works well. He recommended against freezing your seeds. High heat will also shorten the storage life of seeds.
He has germinated tomatoes seeds that were 50 years old that had been stored correctly. On one occasion, he received wheat seeds (wheat berries) from a cave in South America that were several hundred years old and they germinated.
If seeds fail to germinate, he said it is often because the seed coat has become hard. He said that you can soften the seed coat by soaking in them in a mixture of two parts water to one part chlorox for thirty minutes. Then rinse them in clean water and plant. This will not always work but is well worth a try. He told me the story of another Professor who had some tomato seeds that would not germinate so they were fed to his turtle. After going through the digestive track of his turtle, the seeds were then discovered to germinate.
The length of storage life varies from plant to plant. However, most plants seeds should last a few years. Legumes have a short shelf life compared to tomatoes.
The following is additional information that comes from the University of Colorado.
- Vegetable and flower seeds may be kept for one year without appreciable decrease in germination.
- Storage may be extended to 10 or more years under proper conditions.
- Seed moisture and storage temperature are the most important factors in determining how long seed can be stored.
- The drier the seeds are, the longer they will store.
A 10-year storage life can be achieved by drying seed to less than 8 percent moisture. To do so, dry seed at 100 degrees F for six hours. Obtain this temperature by spreading the seed out in direct sunlight. However, because sunlight is harsh and easily can exceed this temperature, drying in the shade is better.
When seed moisture and storage temperatures are low, the presence of oxygen has not been shown to be a factor in seed longevity. Germination is unaffected by storage in atmospheres of nitrogen, carbon dioxide, partial vacuum or air.
Beans and peas are particularly subject to the seed coat hardening therefore should not be dried as completely as other seed. If they have been over dried, they germinate better if exposed to a humid atmosphere for two weeks before planting.
I mentioned that he did not recommend freezing seeds. The problems are several. If you have frost-free freezer the temperature varies during the defrosting cycles. Seeds need to be thawed out slowly; a sudden exposure to hot humid air can cause them to become moldy and not germinate. Some tropical seeds cannot tolerate freezing.