How to Save Seeds: Drying Seeds for Storage

Enlarge Image Image Gallery Learn how to collect, save and cultivate seeds from more than 300 vegetables, herbs, fruits, flowers, trees and shurbs with "The Complete Guide to Saving Seeds." Authors Robert Gough and Cheryl Moore-Gough thoroughly explain every step in the seed-saving process.

The following is an excerpt from The Complete Guide to Saving Seeds by Robert Gough and Cheryl Moore-Gough (Storey, 2011). The excerpt is from Chapter 4: Seed-Storage Know-How. 

Seed-Drying Methods 

Drying seeds to the desired moisture level for storage may take a few days to several weeks, depending upon the species, the atmospheric humidity, and the equipment you use. The faster you dry the seeds, the less likely they will be to succumb to pathogens. The lower the humidity of the air in which the seeds are placed, the faster the seeds will dry. Seeds dry quickly at first, then more slowly as their moisture content nears that of the air around them.

Packaging Seeds for Drying 

Small coin envelopes work very well for holding seeds while they dry, better than standard paper letter envelopes, which often have small holes at their corners through which tiny seeds can spill out. Another option is to wrap small seeds tightly in pieces of paper towel and secure the seams with tape. Whether you use envelopes or paper towels, package only a few seeds together. If you have a lot of seeds, you’ll have to use a lot of envelopes. Be sure you carefully label each envelope or paper towel with the date and the crop or species name (and the variety name if there is one). Note that although plastic bags and glass jars work well for storing dried seeds, they are not good container choices for seeds during the drying process.

Dehumidifier Drying 

If the air in your home is damp, as is often the case in coastal states and in the South, set up your seeds in a small room with a dehumidifier. You can use an inexpensive hygrometer and a thermometer to estimate how dry seeds are by tracking the relative humidity and maximum and minimum temperatures in the drying room. Measure the relative humidity and temperature daily.

Leave the seeds in the drying area for at least a week to be certain their moisture has come into equilibrium with that in the air. Ideally, follow this rule of thumb: The sum of the relative humidity and the storage temperature in degrees Fahrenheit must not exceed 100, as long as the temperature is less than 50°F (10°C). For example, if the relative humidity in your drying room is 40 percent and the temperature is 40°F (4°C), then the sum is 80 (40 + 40), which is less than 100, so your seeds should dry just fine.

Most orthodox seeds will dry to an ideal 6 to 8 percent moisture if they’re held at 38 to 40°F (3.5 to 4.5°C) and 30 to 35 percent relative humidity. Seeds of recalcitrant species like those of the oaks will dry to their appropriate moisture content if held at 38 to 40°F (3.5 to 4°C) and about 40 percent relative humidity. As a homeowner, you don’t have the wherewithal to purchase expensive moisture meters to be absolutely sure of having perfectly dried seeds, but these schemes will get you into the ballpark. The graph on page 52 illustrates the relationship between the relative humidity of the drying room and the approximate moisture content of the seeds. You can easily see that keeping the relative humidity below about 40 percent will reduce the seed moisture to below about 8 percent, although more exact percentages depend upon species and seed lot. The table below gives some specific examples of the expected moisture content of vegetable-crop seeds when dried at 40°F (4.5°C) at 45 percent relative humidity.