Collecting seeds

Toward the end of the growing season, many plants begin to produce mature seeds. This is the perfect time to collect them if you'd like to grow new plants next year. Seed collection is a wonderfully frugal and fulfilling way to propagate your favorite perennial plants, and it's also essential for carrying on any annuals' legacy. When collecting seeds you’ll also often get more than you can sow yourself. Why not share or trade your excess seeds for new interesting plants with other gardeners?

Harvesting and preparing Seeds

Timing your collection

In most cases, a seed must mature fully while still attached to the plant to ensure it can survive storage and maintain a high germination rate. This means you should wait until the seed capsules, berries, or fruits have completely dried or ripened on the plant before you harvest them.

You’ll often know a seed is ready when the seed pod or capsule changes color (usually from green to brown or tan), the pod rattles when gently shaken (a sign the seeds have detached inside), or when fleshy fruits or berries are fully ripe and about to drop off, or at least detach more easily the plant.

Drying and storage preparation

For many plants, the next step is to dry the seeds before storage. This minimizes the risk of mold and preserves viability. First, carefully open the dried pods or clean any flesh and pulp away from the seeds inside fruits and berries. Next, spread the seeds out on a plate, tray, or paper towel. Allow them to dry indoors at room temperature in an area with low humidity. A week is usually long enough for the seeds to dry sufficiently for long-term storage in seed bags or envelopes. Make sure they are completely dry before sealing them up.

For plants with seeds embedded in a gooey gel or sticky flesh, such as tomatoes, cucumbers, or passionfruit, one effective method is to ferment them. First, scoop the seeds and surrounding gel from the fruit, add some water, and let the mixture ferment at room temperature for about a week. This process helps the seeds detach from the flesh and other substances. Next, rinse the seeds a couple of times in clean water. The viable seeds will sink to the bottom, while the pulp and non-viable material will float. Drain off the debris and excess water. Finally, spread the clean seeds onto a piece of aluminum foil or a screen to dry completely before storing them. This method results in clean, easily separable seeds that are ready to sow in the following years.

Some exceptions: seeds with short viability

Not all seeds can survive the drying process. Some have a short, critical window of viability after picking. These exceptions must be sown immediately, or at least as soon as possible after harvest for the best results.

For hardy perennials, shrubs, and trees in colder climates (like peonies, hellebores, cyclamen, viburnums, oaks, and maples), sow the seeds in pots and place them in a sheltered outdoor location during the fall. This keeps them naturally moist and provides the necessary cold stratification over the winter.

For houseplants and tropical plants (such as anthuriums, monsteras, and philodendrons), sow the seeds as soon as they mature. These usually require warmth and high humidity to germinate successfully.

Storing your collected seeds

Once your seeds are fully dried, proper storage is crucial for maintaining their viability. Seeds that tolerate drying can last for at least a year, and sometimes many years, depending on the species and the storage environment.

Optimal storage conditions

To give your seeds the best chance of survival, follow these general guidelines:

• Dry- Seeds must be completely dry before storage. Moisture is the enemy of viability and encourages mold.

• Dark- Store seeds away from light, which can otherwise degrade them over time.

• Cool and stable- Keep them in a location at room temperature or slightly below if you can. Stable temperatures are better than fluctuating ones.

Packaging your seeds

The container you choose plays a role in successful long-term storage. Paper bags or envelopes are preferred. Paper is the best option because it allows any residual excess moisture in the seeds to escape.

Plastic bags are best used with caution. Plastic can be used, but only if the seeds are fully dried already. If there is any moisture present, plastic will trap it, causing condensation and leading to moldy seeds or even unwanted germination if it's really moist. If you decide to use plastic bags, let the seeds dry for a couple of weeks before just to be safe.

Maximizing viability with cold storage

Totally dry seeds can be stored in a refrigerator for extended viability, as the cold slows down the metabolic rate of the seed. some important notes on cold storage:

• Stability is Key - Repeatedly warming them up and cooling them down (by taking them out and putting them back in often) can actually reduce viability. It is best to minimize the number of times you move seeds out of the fridge once they are placed there.

• Avoid for Tropicals - This method should not be used for seeds of tropical plant species, as they are not adapted to cold temperatures.

Seed Longevity

How long do they last? It depends on the species. Some plants like parsnips will get a severe germination rate drop after the first year, while tomato seeds can last up to 10 years or even longer given an optimal and stable environment.

Some tips

• It can sometimes be easier to collect whole seed heads, then use a bag to shake them and more easily get out the seeds once they're dry.

• You can put a small mesh jewelry bag over seed heads to catch mature seeds. For example on plants with seeds that fall off easily once mature, or are otherwise easily dispersed by the wind.

• If you want to limit cross pollination between varieties of the same species, cover the flower buds before they open up with a mesh bag. Then manually pollinate or self-pollinate the blooms once they open. This stops insects from visiting the flower with pollen from other varieties, and thus prevents cross-pollination. The resulting seeds should have a higher chance of turning out as the parent plant.

• For annual plants that readily re-seed themselves you don’t always need to collect the seeds. They are often favored by having some open, exposed soil to germinate in the following year. Make sure to remove any coarse mulch, weeds, or competing perennials to expose some bare soil. You can then sprinkle the seeds right from the seed heads on this area.

• Don’t forget to write the name of the plant you’ve collected, as well as the date and location on the seed bag. It’s easy to forget which seeds come from which plant otherwise, or how long you’ve had them in your seed collection.

• If you’re not collecting seeds in your own garden, make sure to ask the land owner for permission (many say yes). Or if in the wild, make sure that it’s not an endangered species, and that you’re allowed to collect seeds of this plant in the particular area. Do not collect seeds in botanical gardens unless you have permission to do so. Many botanical gardens collect seeds from their plant collection to be used in species protection programs, research or to help finance their work.

• Collecting and sowing seeds can result in new variations and interesting seedlings, and ca be a way to create new varieties. Coleus plants are a good example of this when it comes to houseplants.