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Giving Seeds What They Need In Storage
by Fred Davis, MG, Hill Gardens of Maine (To view other articles, click: Archives)


Welcome through Fred's Garden Gate! On a recent visit to the home of dear friends—a family blend of professionals, gardeners, homemaker, outdoorsman, and delightful youngsters—we brought along a package of choice vegetable seeds that I knew would be accepted with appreciation, and probably shared with several of their friends as well. My heart sank as our host retrieved a Tupperware container from a cabinet above the stove. In it were small, labeled paper envelopes containing an assortment of their cherished seeds carefully saved from the previous season. 

Temperatures in this cupboard that Thanksgiving Day had to have been over 90-degrees—in all likelihood, they must frequently have soared to well in excess of 120 as large dinners cooked and scrumptious desserts baked. Humidity levels must almost certainly have wildly fluctuated between a parched zero and a sloshy 100% as torrents of steam bathed those cabinets as well. Hot and cracklin' dry one day, hot and tropic-wet the next! 

As you might already have guessed, those are not the ideal seed storage conditions. So, how and where should they be kept to maintain vigor and viability?

First, consider that only drying-tolerant seeds (those that can handle drying out) will enter into the following discussion: virtually all common flowers, herbs, vegetables, shrubs, and a great many trees. Drying-intolerant types—aquatics, some large-seeded plants, and the nut-like seeds of a number of trees like oak, chestnut, ginkgo and buckeye, for example—are normally planted fresh, and are usually not storable. In their natural setting, drying-intolerant seeds fall to the ground and then immediately germinate.

Nature—whose methods are age-old, tested and proven effective—almost always gradually matures and dries seeds on the plant. Nature has learned that, as seeds undergo this drying and transition from active growth to full dormancy, important physiological changes occur as food reserves convert from vulnerable sugars to more stable (storable) fats and starches. In this more stable condition, a broad range of seed types can be stored for sometimes years. . .assuming optimum storage conditions are maintained. What are those ideal conditions?

As a general rule, humidity levels within the storage environment should be maintained in the range of 25-35%. The average home during northern-tier winters is exceptionally dry—often dipping into the low teens. Low humidity draws moisture from delicate seed structures and exerts a negative impact on vigor and germination rate. Drying seeds to zero moisture will, of course, destroy them. The rule: once seeds have dried (cured) to the correct moisture level (by weight), unless you have the kind of precisely-controlled storage conditions employed by seed companies like Johnny's Selected Seeds in Albion, Maine, store yours in sealed, air-tight containers like glass jars or doubled Ziploc bags. In the highly variable home or small farm environment, paper envelopes, cloth bags, or cardboard boxes allow for exchange of far too much (or too little) moisture for long-term storage.

Temperature, of course, must be maintained within a relatively narrow range. I've heard it said that the home freezer is the best place. Personally, I question the advisability of freezing temperatures in one- to two-season storage. While it is true that many seeds will store almost indefinitely if deep-frozen, those who have done the research recommend short-term home storage between just above freezing, to about 40- or 45-degrees.  Properly sealed after drying, I've found an ideal location to be on the cellar floor in a corner furthest away from heat sources such as furnaces, water heaters, or warm-air ducting. Our new "root cellar"—an enclosed, insulated crawl space beneath our recently reconstructed solarium— to be perfect for our seed storage needs at a comfortable 25% humidity and 42-degrees (F) nearly constant temperature.

Darkness is the third, yet equally important, requirement. Bear in mind that certain conditions (moisture, temperature and light—especially in some combination thereof) stimulate and support the process of germination—sprouting.  Just as many foods, pharmaceuticals and chemicals rapidly deteriorate when exposed to light, so also is seed viability and vigor impacted by being exposed to illumination during storage. That cool corner of the cellar or root/vegetable storage area should also be very dark. The worse possible scenario: a sudden change to warmth, elevated humidity and light during mid-winter storage, followed by chilling, drying and return to darkness. Kiss them goodbye!

Seed storage problems:

Mildew or Mold. Seeds not dried to the correct moisture level before being sealed in glass or plastic, can—and do frequently—rot. A simple test: After "drying" and placing in closed glass jars or plastic bags, the appearance of condensation on the inside of those containers within a few hours indicates the need for further drying. Stay right on this one because damp seeds will decay (and die) very quickly!

Insects. Weevils, borers and small beetles that may have escaped notice will wreak havoc on stored seeds. A few pinches of diatomaceous earth (DE) is a safe, inexpensive, prudent, and non-toxic bit of insurance against insect damage. DE is available at some farm 'n garden stores and larger garden centers. It doesn't take much; just be sure to lightly coat all seeds before final sealing and storage. Avoid the use of powerful commercial insecticides.

Rodents. Seeds in storage, unless precautions are inaugurated, can provide a virtual banquet for mice or other small vermin. Prevent damage by placing labeled seed containers in either metal or plastic storage containers, or enclose them in an unused picnic or camp cooler. Please don't use tanglefoot traps to capture, terrorize, and torture mice. 

       Following the above easy "rules" will ensure longevity and viability of the seeds of a new generation of flowers, herbs, fruits and vegetables. Have a warm, safe and pleasant winter and holiday!  

 Extensive list of flower and vegetable seeds, and how long they'll last in as close to ideal storage conditions possible in most homes.


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