Tip of the Week: Cleaning, Drying, and Storing Seeds

Posted in Gardening Tips on November 15 2010, by Sonia Uyterhoeven

Sonia Uyterhoeven is Gardener for Public Education.

Last week I blogged about the process of collecting seeds. Once gathered, the seeds will need to be cleaned and dried before they can be stored.

Some seeds require only minimal cleaning while others need more attention.

If you are collecting seeds from non-fruiting plants, gather the seeds on a dry day. Spread the seeds on newspapers, in a cardboard box, or in an old telephone directory, and allow them to dry between one and three weeks.

Often seeds need to be separated from the chaff (the seed casings and debris). You can do this with a pair of tweezers; not all of the chaff needs to be removed, but just cleaned off a bit.

A simple way to separate chaff from seeds is to make a deep crease down the center of a piece of paper. Place the unclean seeds in the center, tilt the paper at a slight angle and slowly tap the contents out of the folded paper (very similar to what you do when sowing seeds). The contents will separate, with the heavier items moving down the crease faster than the lighter items. If the seeds are heavier they will slide out first, and if they are lighter the chaff will fall out first.

An old-fashioned way of cleaning when the chaff is lighter than the seed (which is common), is to winnow your seeds. Place the seeds in a basket and toss the contents into the air in front of a fan. The chaff will blow away and the seeds will be left to fall back in the basket. If the chaff and the seeds are close in weight the best thing to do is to find a screen that allows the seeds to fall through but traps larger pieces of debris—an old tea strainer or colander works well.

Seedpods are traditionally placed in an old pillowcase and stepped on, releasing the seeds, which are then separated from the chaff. If you are of the culinary bent, place the pods in a bag and crush the pods with a rolling pin.

To clean seeds from fleshy fruits, scoop out the contents and soak them in water. Once cleaned, remove the seeds from the water and dry them on a paper towel. Many people who are serious about collecting tomato seeds ferment the seeds to clean off the fleshy coating (I’ll discuss this process in a future blog entry).

Before storing your seeds make sure they are dry, otherwise they will rot. But don’t desiccate the seed (it is alive)—you merely want to get rid of excess moisture and hold it in a dormant state until you are ready to grow it.

Seeds need moisture, warmth, and light to germinate, so give them the exact opposite—a dry, cool, dark environment—when storing them. Place your seeds in an envelope or paper bag and seal them in plastic containers or glass jars. If you are not convinced that your seeds are dry, eliminate the airtight container step. Remember to keep the labels with the seeds.

Store the seed in a cool, dry place such as a corner shelf in the garage, basement, closet, or in the back of a refrigerator. The ideal temperature for storing seeds is between 32°F and 50°F.

The rule of thumb for storing seeds is that the temperature and the humidity levels should add up to less than 100%. This means that if the temperature is 50°F, the humidity has to be less than 50%. Both high humidity and high temperatures are catalysts for germination and will trigger the seeds’ metabolism.

There are many good books on seed saving. Suzanne Ashworth and Nancy Bubel have written wonderfully informative seed-saving manuals, and William Cullina’s Wildflowers: A Guide to Growing and Propagating Native Flowers of North America is ingenious.