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Seed Saving Primer

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By Dusty Hancock 

Master Gardener℠ volunteer in Chatham County

Seed Saving Primer

Why save seeds from year to year?

You might want to save some money from purchasing new seeds each year. Or maybe you found the perfect tasting variety of a crop and want to repeat that experience again next season. Maybe you just like the holistic approach of following nature’s way of propagation.

Regardless of the reason, you have made a choice to save this year’s seeds and use them in the future.

A word about hybrid/open-pollinated plants and their seed. A lot of today’s top-performing plants are the result of crossing two open-pollinated plants to achieve the hybrid with the best attributes of both parent plants. Open-pollinated plants are usually self-pollinating, but even if they do cross-pollinate with plants of the same variety, the resulting offspring will have characteristics like the parent[1]. Often you will see open-pollinated seeds listed as “heritage”, “historical”, “purebred” or similar terms. You want to save seed from only the most vigorous plants of these open-pollinated varieties.

Seeds from hybrid plants may be sterile, but if not, it is difficult to predict the characters of the resulting offspring. The plants will be a new combination of the best and worst traits of the original parents. [1].

Gather your seed at the end of the season after the plants have matured. You want dry seed and to keep it dry. Seeds contained in a pod or husk should be left to dry on the plant. Each pod can generally be harvested individually as it dries, but if heavy rains or freezing weather threaten, harvest as many as possible. The entire plant can even be removed from the field and hung inside to complete the maturation process[2].

Wet seeds, like those in tomatoes, require you to cut open the fruits and scrape the seeds out. Next, wash the seeds by placing them in a large bowl or bucket. Add water and stir the mixture vigorously. Viable seeds tend to be denser and will sink to the bottom, while poor-quality seeds are more likely to float. Add more water and repeat the process until only clean seeds remain. Pour the seeds into a strainer and wash them under running water. Finally, dry the cleaned seeds by spreading them as thinly as possible on a flat, dry surface such as a glass or ceramic dish, cookie sheet, window screen, or a piece of plywood. Stir the seeds several times during the day [2].

Lest you think I will just put the seeds in your dehydrator to dry them out, know that damage begins to occur whenever the temperature of seeds rises above 95F. Fans hasten the drying process and using a screen to lay the seeds out helps circulation.

Deterioration is slowed when seeds are stored under cool, dry conditions. Temperature and relative humidity should therefore be considered in planning for safe storage. A rough rule of thumb for safe seed storage is that the sum of the temperature (°F) and relative humidity should not exceed 100 units. For example, if the temperature is 60°F, the relative humidity should not be over 40 percent.[3] Refrigerators are normally below 40° but their relative humidity is usually in the 65% range, above our 100 unit guideline. This also assumes you are not frequently opening the door allowing the temp and humidity to increase.

A general rule is that each one percent decrease in moisture content of the seed or 10°F decrease in temperature nearly doubles the safe storage period. It is important to put dry seed into storage and keep it dry[3]. Vacuum-packed seed may remain viable for several years but needs the seed moisture to be 2-4% lower than that required for conventional storage.

Your options with dry seed:

  1. Vacuum pack very dry seed and keep in the refrigerator.
  2. Place dry seed in airtight containers and place in the fridge.
  3. Place dry seed in airtight containers and keep it in the coolest place in your house, not to exceed 95° F.

If both temperature and moisture cannot be regulated, then moisture is the most critical factor to be controlled. Good luck!

For more information, see these additional Extension resources:

[1] Saving Vegetable Seeds – University of Minnesota Extension

[2] Seed Saving Basics – Maud Powell, Oregon State Extension Service

[3] Seed and Seed Quality – NC State Extension