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Seed saving 101: How to safely store the seeds from this year's vegetable garden

Gardening pros on why you should save your veggie seeds — and how to create a library you can sow for years.

Gardening pros on why you should save your veggie seeds — and how to create a library you can sow for years

closeup on broad bean seeds spilling from a paper envelope onto wooden surface next to plant pot, twine and wooden garden stakes.
(Credit: iStock/Getty Images)

Getting to finally harvest what you've grown can be a rewarding experience for any new vegetable gardener. It's proof that all the sweat — and perhaps some tears — have paid off. And though it may be tempting to collect your garden's full bounty, if you let some of your plants mature, it will give you the chance to save their seeds and sow them for years to come.

We spoke with two gardening experts about why you should consider saving your vegetable seeds and how to do it right.

Why save your seeds

There are many benefits to seed saving, says Emily Murphy, author of Grow Now and Grow What You Love. Not only does the process encourage us to pay closer attention to the life cycle of our plants, helping us to become more capable gardeners, but it also creates the opportunity for us to grow stronger plants, as they adapt to the individual microclimate of our garden over time, she explains. On the practical side, having your own seeds also means not having to rely solely on stores, which may have limited availability or may not carry the varieties you're looking for.

One more reason to save seeds? It's fun! The practice of harvesting, building a library and even participating in a seed exchange with fellow gardeners can be gratifying all on its own.

When to do it

The optimal time for harvesting seeds will depend on the plant and its life cycle, says Jon Peter, curator and manager of plant records at the Royal Botanical Gardens. Vegetables can generally be broken down into two categories: cool season and warm season crops. Cool season crops, such as lettuces and radishes, can be sown in the early spring and also in fall, so they may be among the first and last plants in your garden to fully mature. Meanwhile, warm season crops, like tomatoes and cucumbers, which we typically don't plant until the frost has ended, will reach their peak in late summer. That means, depending on which vegetables you choose to grow, you could be harvesting seeds from late spring through to late fall, Peter explains.

Tips for harvesting seeds from common vegetables

Much like seemingly every other process when it comes to gardening, harvesting seeds is species-dependent. Because of that, Peter says it's really important to dig down and do the research on each specific type of plant that you'd like to save seeds from. One key element is learning the life cycle of the plant and what it looks like when its seeds mature. 

Here are some tips for harvesting the seeds from a few common vegetable crops. 

Onion

Leave the onion bulb in the ground and wait for the plant to flower. "It's a really beautiful flower and the bees love it," Murphy said. "And when it starts to go to seed, it produces these really neat little black seeds that have edges on them." She suggests leaving the seeds on the plant and gently shaking the seed head into a paper bag to collect them.

Kale

Similar to broccoli and cauliflower, which are of the same species, kale has to flower and sit past its prime picking time for its seeds to be ready to harvest, Murphy explains. Kale produces long, skinny seed pods, and when they go dry, you can either collect the whole pod or cut the seeds off individually and put them into a paper bag, Murphy says.

Peppers

In cooler climates, like Canada's, peppers are grown as warm season annuals that mature later in the summer. Nearly all varieties of peppers will turn red when they're fully ripe or overripe, Peter explains. "We want to let it go overripe and almost start to decompose on the plant, if you will, and then you can open up that fruit and basically scrape away or flake away those seeds that are attached to the inside and lay them out on a paper towel for a night or two," he said.

Carrot

When a carrot fully matures, it creates an umbel (think umbrella) of flowers, says Murphy. Once the flowers are pollinated, the seeds form and become visible throughout the umbel. You can let them dry on the plant and then shake them into a paper bag. Another technique? Murphy says that some people like to put a paper bag over the plant itself to avoid losing any seeds — though that's not a method she personally follows. She prefers allowing some seeds to set on their own, as these "volunteers" can provide valuable information on a plant's growth patterns that you can use for years to come.

Beans and peas

Before harvesting, Peter recommends waiting until the plant's leaves "die back" (meaning when the leaves are dead, but the roots remain alive). The seed pod will turn brown and the dried seeds will even start to rattle a bit inside. "You want to get them just before they're kind of popping open, and release the seed naturally," he said.

Zucchini

Leave the zucchini on the vine until it turns yellow, recommends Murphy, letting it ripen there as long as possible before harvesting. You can then scoop out the seeds from the zucchini and let them dry.

Generally, Murphy recommends letting one plant per vegetable crop go to seed. This will still give you plenty of seeds to store, share or exchange. One zucchini plant, for example, could produce as many as 50 seeds, she says. And saving just one plant to go to seed will open up more space in your garden to start planting the next season's crop, too.

Drying your seeds

Before drying your seeds, it's important to ensure they are clean. Some seeds, such as those from pepper plants, will be fairly dry and clean when you collect them, Peter says. But others, such as ones from zucchini, will have pulpy matter around the seed that needs to be washed off in order to prevent mold and rot. Be sure to wash those seeds, then pat them dry and let them sit on a paper towel for a day or two out of the direct sun — ideally, in a spot where there's less humidity, Murphy says. The more moisture in the air, the longer it can take for certain types of seeds to fully dry out, increasing the chances of mold, she explains.

So, how do you know when your seeds are truly dry? Just try to get as close as possible and trust your intuition, says Murphy. "If it looks dry and it feels dry — or nearly so — then it probably is."

How to store your seeds (and create a seed library)

Once the seeds are clean and dry, it's important to keep them in a cool, dark place. "Now, technically, with seeds, the best way to keep them for long-term viability, is to keep them in an environment that's the exact opposite of what you grow them [in] — so in a place where there's no moisture, no light and it's fairly airtight," said Murphy. This will help keep the seeds in dormancy longer, she explains. However, if you plan on using the seeds within a couple of months, an airtight seal doesn't matter as much. Murphy stores her bulkier seeds in brown bags in cool, dark places, and her other seeds in seed keepers: little airtight boxes that are compartmentalized and indexed alphabetically.

Peter likes placing his seeds in paper envelopes to keep the moisture away, before storing them in an airtight container in his beer fridge. In this state, he finds that some seeds can last several years. "I'll take a few seeds out of a package each year, but then I'll put that package back into its storage for the next year," he said. 

If dried and stored correctly, Peter says short-lived seeds (that is, seeds with a shorter shelf life), such as corn, onion, parsnip and spinach, can typically last one to two years. Medium-lived seeds, like carrots, beans, celery, chard, eggplant, peas, pumpkin and squashes, may last up to five years, while long-lived seeds, which include broccoli, cauliflower, cabbage, cucumber, kale, lettuce, melons, peppers and radishes, may last for many years longer.

Ultimately, like most aspects of gardening, harvesting seeds is all about trial and error. But that's precisely what makes the process exciting, says Murphy. It's being curious about what worked, what didn't work and how you can do it again better next year.


Janet Ho is a writer and gardener in the making. You can follow her at @janetlynho. 

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