A Seed Saved: How to Harvest & Store Plant Seeds

Planting a seed where you—not nature—decides is a powerful activity. Vast cities have sprouted near-rich farmlands, and whole cultures have revolved around the dynamic contributions of specific plants to human life and culture. All of that would have been much more difficult, if not impossible, without the ability to harness the vitality and mystery of the humble seed.

This Isn’t Your Grandma’s Seed Stock

Saving seeds at home used to be a much more common activity than it is today. During the first half of the 20th century, it wasn’t unusual for families to maintain backyard gardens containing heirloom, open-pollinated plant varieties. In fact, in 1943, at the height of the Second World War, an estimated 40% of produce consumed was grown in victory gardens located primarily on private lands. Seeds for those vegetable gardens were probably sourced locally and later harvested from those backyard gardens.

Although times have changed, growing produce and other plants at home has seen a resurgence during the last decade or so. Is preserving seeds a simple process? Sure, it can be. But there are more factors to consider than there were 70 years ago. Scientists have been hard at work tinkering with plant genetics, which means there are lots of hybrid plants available that may look and taste great but not reproduce true to the original plant. Part of the art of saving seeds is recognizing which ones are good candidates for preservation, and which aren’t.

Natural Selection Isn’t Just About the Birds and the Bees

Preserving seeds from your best plants is a good way to cultivate strains that are well-adapted to your specific growing conditions, indoors and out. It’s natural selection, with a little friendly encouragement. You don’t need to be a geneticist to do it, either. The seeds you choose to preserve and plant later are probably from the hardiest plant specimens. When you save those plant seeds, you preserve the very traits new plants need to survive in your landscape, greenhouse or grow tent.

A Seed-Saving Primer

The conditions you need for good seed germination (warmth and moisture) are the opposite of what you need for good seed preservation. Seeds may look tough and self-contained, but they’re designed to react to the environment around them. When you remove enough moisture and keep them chilled, they stay dormant, waiting for conditions to improve. Some experts believe a seed that’s kept dry enough and at a consistently cool temperature can last a decade or sometimes much longer. For the home grower it can vary, but a good general rule is high-quality seeds should last two to three years if stored carefully. Larger seeds will typically remain viable somewhat longer than smaller seeds. Here are some important steps for saving seeds for future use, trade or sale.

Avoid hybrid seeds – With hybrid seeds, what you see isn’t necessarily what you get. Hybridization is a complex process in which two separate-but-stable plant strains are cross-pollinated to produce a third plant variety that hopefully exhibits the best characteristics of both parent plants. This second generation plant is typically referred to as an F1 hybrid. When it matures and sets seed, the seedlings may be more like one of the grandparent plants, or could exhibit completely unexpected and unwelcome characteristics. If you’re a gambler, go ahead and give hybrids a try. If not, check the labeling on the plants you purchase to make sure they are heirloom stock or open-pollinated cultivars.

Choose open-pollinating plants for seed stock – The term open-pollinated can be somewhat deceptive. It sounds like a random process that can lead to more chaos and potentially bad seedlings than a hybrid cross. It turns out nature is pretty clever, though. Open-pollinated plants, or plants that have developed in nature over time without human intervention, produce reliably consistent results. Generation after generation, these seeds will produce plants similar to the parent plant. This makes them excellent candidates for future cultivation. The one exception is when an open-pollinated plant cross-pollinates with a closely related plant. This can sometimes occur when plants from the same genus and species are grown in close proximity to one another. To avoid surprises, grow only one genus and species variety at a time unless you can keep similar specimens completely separate. A plant’s Latin name will provide important clues about its likelihood of crossing with other plants in your collection.

Choose seed plant specimens carefully – Small variations may make their way into future generations of even non-hybrid plants. If you’re collecting seeds instead of cloning plants, a little variability is inevitable. The trick is to hedge your bets by selecting plants for seed that represent your wish list for future generations. This can include things like hardiness, flavor, flower color, size and so on. Most experts agree it’s better to settle for fewer seeds overall than to harvest seeds from inferior plants. When you’ve made your plant selections, allow those specimens to dedicate their energies to setting seed. Once a plant goes into seed production mode, it has little energy left over for other types of activity, like producing additional leaves or flowers. Recognizing which plants you want for seed early in the growth process is one key to a good seed harvest.

Don’t harvest seed too soon – When it comes to harvesting seeds, timing is important. As gardeners, we’re used to harvesting plant products when they’re flavorful or at their most attractive. Flowers, fruits and vegetables typically produce mature seeds late in the growth process, though, usually after the flowers have withered, the pods have dried completely or the fruits have become overripe. When in doubt, wait. An immature seed will never sprout, so give seed stock plenty of time to mature.

Is that a seed, a bit of fluff or a twig? – It would be nice if all plant seeds looked more or less identical, but it doesn’t work that way. Seeds can look like dried petals, twigs, fluff, dead worms or other unremarkable things, or they can be so small they are difficult to see. Before you grab your harvesting kit, familiarize yourself with the appearance of the seeds you’re after so you won’t be disappointed later.

Dry seed processing – Although there are many plant varieties, most seeds are harvested using either a dry or wet processing method. Dry processing is about what you’d expect: allow seed heads to dry completely, preferably on the plant. Transfer seeds to a screen or other surface where they can be separated from extraneous plant material. If seeds can’t be dried completely on the plant, they can be transferred to a paper bag, or flowering heads can be suspended by their stems in a warm, dark location for additional drying.

Wet seed processing – Wet seed processing is used to prepare seeds from fleshy fruits like melons. Some quasi vegetables are handled in this way as well, including cucumbers and tomatoes. Fermentation is part of the process, which means the seeds aren’t dried on the plant. Instead, they’re removed from the fruit along with some of the pulp and allowed to mellow through the actions of naturally occurring yeasts. This typically takes a few days. Here’s how it works: A slurry of seeds, pulp and water is allowed to ferment in a cup, bucket or other wide-mouth container that is shaken or stirred regularly. Viable seeds eventually sink to the bottom of the container, while the pulp and non-viable seeds float to the top where they can be skimmed off. After five days or so, the seeds are removed and dried on a screen or paper plate, in a mesh bag or on another neutral surface. Different seed experts have their own methods for processing wet seeds, but they typically follow this similar pattern.

Seed cleaning – After drying, be sure to remove any debris from seeds before storing them. The presence of extra stuff can encourage mold or bacterial growth. Some veteran seed collectors recommend freezing prepped seeds for up to three days to kill any incipient bacteria or mold they may be harboring. A clean seed is a safe seed. Removing good seed stock from the surrounding chaff can be tiresome, but threshing and winnowing are both time-honored methods for removing large and small bits of debris from seeds. For the casual gardener, placing dried seeds on an old window screen and gently shaking the screen can help separate stem pieces, bits of leaves and partial seed casings. Employing a small, hand-held fan can also help.

Controlling temperature and humidity – The two most important factors when storing seeds are temperature and humidity. The temperature part of the equation can be pretty simple. Keep seeds in a refrigerator if you can. Other good choices are in a dry basement or root cellar. The humidity part can be tricky. For the pros, the optimal humidity for seed storage may be less than 8%. For the home grower using conventional drying methods, it probably hovers around 25% or so.

Low humidity is achieved by choosing seed containers that seal well, paired with desiccants like silica gel that absorb ambient moisture. Seed savers have been using do-it-yourself moisture absorbers for a long time, including powdered milk, dried rice and non-clumping kitty litter. Just keep a layer of cotton or paper towel between the desiccant and the seeds.

Purists often prefer air-tight glass or plastic containers for seed storage. Where space is a problem, some green thumbs like using small envelopes stored inside larger sealable bags. Some popular options include coin envelopes, small parts envelopes, styrene or glass vials with snap-on caps (available for purchase in bulk), sterilized baby food jars and used (and thoroughly cleaned) prescription bottles.

Labeling – Keeping track of seeds can be a nightmare if you don’t maintain good records. Starting a gardening log is a good idea, but even if you aren’t into taking notes, be sure to label your seed stores carefully. The experts recommend including the plant’s Latin and common names, the date the seeds were collected and any special information you may think you’ll need later. This can include the source of the original plant or starter seeds you used, and what you want to achieve with your next crop.

Preserving seeds successfully requires some trial and error, but the process can be fun and rewarding. Growing your own seed is a nice way to re-create a gardening success, share your carefully cultivated good fortune with others or just save money the next time around. So, save your seeds. It’s the smart thing to do!