Once you have grown out your seeds and are ready to save seeds for next year, make sure the plants are healthy and disease free with no visible insect infestation. Select for qualities that you value: earliness, vigor, size, color, and taste. Don’t wait for the last of the crop to save seeds (unless you are selecting for lateness!). Cull out any rogue plants that don’t meet up to your standards for the type of plant you are growing.
Seeds that are ripe enough for saving when the fruit is fully mature and still edible are tomatoes, eggplant, and peppers. Overripe is fine for these as well if you want to leave them to ripen on the plant without eating them. Seeds from squash and cucumbers are best saved from over-ripe, yellowing fruit that has gone past the eating stage. Crops that form pods or seed heads like beans, peas, okra, herbs, and flowers should be allowed to ripen and dry naturally.
Dry Seed Processing is the method is used for seeds that dry naturally on the plant and fall down to the ground to germinate the next spring. These seeds include lettuce, onions, grains, brassicas, beets, carrots, beans, and peas. Seeds must be gathered when dry but before the seed pods shatter and the seeds are lost. Dry pods and seed heads are best gathered over a large bag or large bowl to prevent the seeds from falling out onto the ground. Small amounts of seed can be cleaned by hand, but for large amounts you will want to remove the seed from seed heads by knocking them into a container such as a clean garbage can or onto a sheet or tarp. This is called “threshing.” Once that is accomplished you will have to separate the plant debris, or chaff, from the seed one of two ways. You can “winnow” the seed by pouring it from one container to another in a breeze or in front of a fan to blow away chaff. This is best done outdoors. You can also sift the seed through a screen or sieve to remove chaff.
Wet Seed Processing is used when the seed is encased in a fleshy fruit, such as tomatoes, eggplant, peppers, and squash. Remove the seed from the fruit and rinse clean, or soak in a jar for a few minutes until the seeds sink and the debris floats. Spread the seeds on newspaper, paper plate, or paper towel and allow them to dry thoroughly. Pat the seeds dry and allow them to completely air-dry on newspaper or paper towel.
Fermentation Seed Processing is used when the seeds are not easily separated from the fruit and cleaned. There is often a thin, gel-like substance on the seed that is hard to remove and it will sometimes inhibit germination. This is most common with tomatoes but cucumbers and melons may need this process as well. Place the seeds in a jar with some water and allow the mixture to ferment for a couple of days until the seeds drop to the bottom and the debris floats to the surface and gets moldy and ferments. Pour off the water and rinse the seeds in a colander or sieve with holes smaller than the seeds. If the seeds do not rinse clean repeat the process. Spread the seeds on newspaper, paper plate, or paper towel and allow them to dry thoroughly.
After processing, all seeds should be placed in a moisture-proof, insect and rodent-proof container and stored in a cool, dry place away from light. Use baggies, envelopes or packets and store the packets in plastic tubs or large jars with tight-fitting lids. Be sure to label all seeds with the plant name, variety name, and year gathered. If you have room, you can store them in a refrigerator or freezer but you have to make sure the packaging is airtight. When properly stored, some types of seed can last for years.
If you are concerned about the viability of your seeds, test their germination before planting time. Put ten seeds on a moist paper towel and place it in an unsealed plastic bag. Date bag and keep the towel moist but not soggy. Seeds should germinate in 3-10 days. If the germination rate is low, or if the seeds begin to mold before germinating, get new seed.
What follows is a list of commonly grown crops and how long you can expect the seeds to last if stored properly:
- Squash & Melons 4 years
- Beans & Peas 2-3 years
- Onions 1 year (freeze for longer)
- Beets, Spinach, Chard 4 years
- Broccoli, Cabbage, Kale, Radish, etc. 4 years
- Peppers & Eggplants 3 years
- Carrots 3 years
- Spinach 4 years
- Corn 1 year (freeze for longer)
- Tomatoes 4 years
- Lettuce 4 years
- Parsnip & Parsley 1 year (freeze for longer)
After you have set aside enough seed for your own garden, consider donating your extras to the LTPL Seed Sharing Library. Bring your clean, dry seeds to LTPL in a clean envelope or jar. (Please use recycled containers and return envelopes from your junk mail) Fill out a seed donation form for each variety of seed and tape or staple it to the container. Place your container in the seed drop-off box. The seeds will be packaged and filed in the Seed Sharing Library by a volunteer.