A trellis covered with pea or bean vines provides a barrier between squashes than can prevent accidental cross-pollination by wind and lessen the chance that pollinating insects will travel from one variety to another.
Once you’ve decided which crops and varieties you want to save seeds from, make seed saving part of your overall garden plan. It’s easy to do, and you’ll get the best results if you plan ahead. Figure out how you might need to adjust planting times, gather the equipment you need for seed collection and cleaning, and decide where and how you’ll store your seeds.
Think in terms of five stages:
The details of each stage vary from crop to crop, and that’s part of the fun. You’ll find information for individual crops beginning here, but first let’s look at each stage of the process in detail.
Award the crops you’re growing for seed first place on your gardening priority list for the season. Seed-stock plants deserve especially good care because they’re the blueprint for gardening success in the future.
Think about a time when you paid a bargain price for a six-pack of seedlings that were past their prime. Chances are the bargain turned out to be a bother. Even with pampering and extra attention, those bedraggled, weak plants probably didn’t rebound very well and the harvest was a disappointment. The same holds true for seeds: If you start with weak seeds, your crop will be at a disadvantage right from the start. Conversely, the more robust the seed you grow, the better your future crop will be.
For many types of vegetables, the care you give to plants grown for seed production is no different from the care you give to plants grown for a regular harvest. Provide good soil, avoid water stress, and take steps to avoid pest problems (such as using row cover or applying compost tea), and you’ll get good results.
Some crops, though, need special treatment to be the best seed producers. You may need to plant them at a different season than you usually do, or you may need to control the pollination process. Some crops have tall, top-heavy seed stalks that need support. And most biennial crops need protection so they can survive overwintering.
It’s a smart idea to get into the habit of using plant labels and keeping records throughout the gardening season. When you’re looking at plants in your garden, you may find it easy to tell which tomato variety is which even without checking a label, but it’s nearly impossible to distinguish the seeds of one variety from another by appearance alone. You may even have trouble identifying which crop is which. Cabbage and broccoli seeds look very similar, for instance, and so do many kinds of squash seeds. It’s much more fun to share seeds with others when you can identify the seeds with confidence, and a correct ID is critical if you want to save particular heirloom varieties.
Stock up on plant labels at the start of the season, and keep a supply at your seed-starting area and in your gardening tote. Label seedlings in pots, rows, and beds in the garden. Put some brightly colored yarn or flagging tape in your garden tote, too. As the season progresses, use the yarn or tape to mark individual plants that you want to save seed from.
At harvest time, write the crop and variety name on stick-on labels and place them on the buckets, bags, and other containers in which you collect seed heads. Label seeds spread out to dry on plates or screens. And as a final step, label the packages of seeds ready for storage.
If you’ve been gardening for a while, you probably have a finely tuned planting schedule, either on paper or in your head. To add seed saving into the equation, you may need to rethink the planting dates of some crops. For example, a lettuce crop won’t produce mature seed until about 6 weeks after the normal harvesting time. The seed matures best during dry weather. If you have predictably dry summers — or predictably wetter fall weather — schedule planting so the crop matures during the dry period, or at least not during the usual wet season. In humid climates, fall can be problematic for seed maturation because dew takes longer to evaporate on cool fall mornings and the plants receive less direct sun during the day. Overall, plants may spend more time wet than dry, and that sets the stage for mildew and mold, which can infiltrate seed heads and seedpods and infect the seeds, reducing their vigor. Gardeners who live where the growing season is short will need to worry about this the most. The longer your growing season, the more options you have.
Another consideration that affects your planting schedule is that biennial crops need to be overwintered. You’ll want to plan your planting time so that the crop is at the right stage of maturity when cold weather arrives and growth stops. For details on this, see Overwintering Biennial Crops .
Every gardening season brings some surprises and problems. For example, one year you may have your first success at growing cauliflower, but cucumber beetles strike your squash seedlings hard, with very few surviving and bearing fruit. The same variability applies to seed saving. Despite your best efforts, disease or drought may ruin a crop before you can collect seed from it. Resist the urge to save seed from weak and diseased plants. You want seeds from plants that survived the challenges of the season in good condition.
Open-pollinated varieties work well for seed saving because you can count on the offspring having the same characteristics as the parent plants. However, that’s true only when the plant is pollinated by pollen from the desired variety. Corn, squash, cucumbers, melons, and all the cabbage-family plants are subject to accidental cross-pollination unless you take steps to avoid it. You can isolate your crop by distance or barriers, or you can hand-pollinate and protect the pollinated flowers from contamination by unwanted pollen.
The simplest way to avoid cross-pollination complications is to grow only one variety of a cross-pollinated crop. Then you can enjoy watching the insects pollinate the flowers without worrying about the purity of the eventual seeds. You’ll need to make choices, such as whether to grow a slicing cucumber or a pickling variety, but you may be able to grow both in one season if you stagger the crops; plant one early in the season and the other for a late harvest.
Another way to prevent cross-pollination is to plant different varieties far away from each other. How far away, however, is debatable.
Pollen grains differ in size and weight. Corn pollen, for example, can travel for miles on the wind, but squash pollen is heavier and won’t blow as far. How far a particular type of pollen can travel is not a precise calculation — there are too many variables — but through observation over time, horticulturists and farmers have garnered a good idea of how far, on average, pollen might travel. However, they don’t all agree. For example, if you consult several different sources to check the safe distance for separating varieties of broccoli or corn, you might find several different answers.
The answer also depends on how safe you want to be. Commercial seed growers need to play it very safe because their reputation depends on their ability to provide pure seed of the varieties they sell. Home-garden seed savers may not be as concerned if a small percentage of the seed they collect and replant turns out to be not true to type. A recommendation for separating crops may read something like “half a mile, but several hundred feet in home gardens.”
You can also rely on barriers to help limit pollen travel. For example, if your neighbor has a vegetable garden, you could put up a fence or plant a hedge along the property line between the two gardens. Within your own yard, you might grow one variety of squash in your backyard and a second variety in the front yard. There’s no guarantee that a busy bee won’t travel around your house from one patch to another, but the chances are less than if you planted both varieties in the same plot.
A trellis covered with pea or bean vines provides a barrier between squashes than can prevent accidental cross-pollination by wind and lessen the chance that pollinating insects will travel from one variety to another.
Plant breeders and experienced seed savers sometimes cage cross-pollinated crops that are grown close together. The boxlike, bottomless cage is covered with mesh screening. Once the cage is in place over a bed of cross-pollinated crops, the breeder introduces insects into the cage (usually larvae of pollinating flies), and those insects pollinate only that variety. Or the breeder can move the cage back and forth every day or two from one variety to the other, so that each variety is exposed to pollinators but not simultaneously. He or she may choose to continue the cage-changing routine until satisfied that both varieties have been well pollinated, then simply leave the cage in place on one variety until it has finished flowering.
Caging takes real work — both to build the cages and to move them every day or two. Beginners can try an easier variation by covering a crop with row cover to prevent accidental cross-pollination. To do so, install hoops made of sturdy metal wire or electrical conduit along the crop row and spread row cover over the supports. Be sure the hoops are tall enough to cover the crop when it’s in flower. Use lengths of hefty scrap wood or bags filled with soil or stones to hold down the cover firmly.
Using row covers this way can work very well for peppers. Although peppers are naturally self-pollinating, the flowers are quite attractive to bees, and peppers that are planted close together often cross-pollinate. To avoid this, you can cover your peppers with row cover and leave it in place as long as you like. The crop will benefit from the extra bit of warmth and wind protection, though you may find that keeping plants covered all season long can cause stems to become floppy. Experiment with uncovering one row for a period of time to allow plants to be exposed to wind, which will make them sturdier and less likely to topple over. Check periodically for holes in the row cover, too, and seal up any you find with duct tape.
Yet another way to control pollination is to hand-pollinate individual flowers. Try out this technique on squash flowers first, because the flowers are large and easy to handle.
Carrots, beets, radishes, turnips, leeks, and onions are biennial. These crops need a period of cold and rest before they’ll produce flowers and seeds. Usually the cold period happens during the winter, and the plants flower the year after planting. (Spring-planted radishes are an exception.)
Leaving plants in the ground. If your winter climate is mild enough, you can leave some biennial crops in the ground for their cold period. You may already do this with carrots and beets, planting a crop in late summer for fall and winter harvest. In the case of seed saving, though, you’ll leave those roots in the ground until the following spring and allow them to resprout. The plants will produce glorious tall flower stalks topped with hundreds of tiny flowers that attract lots of insects.
If you leave a crop in the ground over the winter, be prepared to lose some roots to hungry rodents, rot, and unknown causes. Plant extra, and hope for the best.
Digging and storing. The other option is to dig up the roots in late fall and store them in a spot cold enough that they won’t grow, but warm enough that they won’t freeze. This method is more work, but it offers an advantage because it allows you to inspect the roots and choose the best ones as your seed-stock plants. It’s also a safer choice in areas with cold winters because plants left in the ground may suffer freezing damage, even under mulch.
Store carrot roots in moist sawdust, sand, or leaf mold to overwinter. Put the containers of roots in a spot that remains a few degrees above freezing.
Carrot plants need lots of space to produce seed stalks. Space overwintered roots 2 feet apart.
Before you start harvesting seeds, be sure the seeds are ripe. Also, have the supplies and tools you need for collecting the seed.
On one hand, if you harvest seeds too early in their development, the embryo inside each seed may not be fully formed; if so, the seed won’t be able to germinate. Or the seed may not have finished packing on the fats and starch that will feed the baby seedling as it begins to grow. On the other hand, if you wait too long, your ripe seed may literally blow away with the wind; drop to the soil surface, where it will blend in and be impossible to find; or end up germinating prematurely inside overripe fruit.
Some seeds, such as tomato seeds, are ripe and ready for harvest when the fruit is ready to eat. Winter squash and melon seeds are also mature in the ripe fruit, but the seed quality may improve if you wait up to 3 weeks after harvest before opening the fruits and collecting the seed.
Seeds borne inside dry pods or husks, such as lettuce and onions, may take several weeks to mature after the flowers first bloom or the young pods form. Here are some general guidelines (for more details on seed ripening, see chapter 3):
As you save seeds of a crop over the years, it’s easy to lose track of the details. Photos can help. Take pictures of your crops every year, and try to record them at the same stages of growth. Your photo record will reveal whether and how your crops are changing in color, size, and shape over the generations. Your photos also provide a record of what fruits or seedpods look like at biological maturity (the time when seeds are fully ripe).
Dry seeds are simple to harvest as long as you’re aware that the seedpods may shatter, breaking open and releasing their seed. Simply pick large seedpods such as pea pods and gather them in a container. For small seeds borne in seed heads, such as those of carrots and lettuce, you can gather seeds individually if you need only a small amount. If you want to save larger quantities, try cutting off whole stalks (a pair of hand pruners works well for cutting the stiff stalks) and bring them indoors to finish drying. To minimize the risk of losing seed as you cut the stalks, plunge the stalks upside down into a bucket or paper bag as you cut them. It’s better to cut the plants than to pull them up by the roots, because soil that has clung to the roots may end up mixed in with the seed, and it’s best to avoid that (see here to learn why).
“Wet” seeds come encased in a fruit. For some wet-seeded crops, harvesting the seed is the same as picking ripe fruit to eat. For other crops, such as cucumbers, the seeds aren’t ready to harvest at the same time the fruits are. The fruits you pick to eat contain immature seeds. When the fruit is fully ripe from a physiological perspective, and the seeds are mature, you wouldn’t want to eat that fruit. It would taste sour and might be starting to ferment inside.
Cleaning and drying seeds are fun projects, and that’s a good thing, because seed that isn’t dry and clean may not store well. The techniques used to clean dry seed are different from those used to clean wet seed.
“Dirty seed” is seed mixed with chaff — pieces of the flower head and bits of stem and leaf. It isn’t essential that you separate seed from chaff, but there are some good reasons why it’s worth the effort:
Two ways to separate seed and chaff are by weight, through a process called winnowing, and by size, using screens.
Seed can also end up mixed with soil, but it’s best to prevent that from happening in the first place if possible. Like chaff, soil can hold moisture and carry disease. But soil tends to be heavy, so it’s not easy to separate soil from seeds by winnowing.
A fun way to separate seeds from chaff is by rolling the seed down a slope. This works best with round seeds, such as radishes, broccoli, and arugula. All you need is a shallow pan or bowl and a section of newspaper or a kitchen cutting board or other smooth board.
Separate seeds from chaff by rolling them down the slope of a folded newspaper.
If you stand outside on a breezy day with a stone held high in one hand and a leaf in the other and you let them go, what happens? The stone will drop straight down at your feet and the leaf will flutter away and gradually drop to the ground. That’s the principle behind winnowing.
Some types of seed are much heavier than the chaff around them. In such cases, you can separate seeds from chaff by pouring them through a mild current of air. The seeds will fall to the ground closest to you while the chaff will travel a little farther away. You can try working with a natural breeze, but using a small electric fan gives you more control.
It’s fun to experiment with equipment to find what works best. For example, you may find that you can pour seeds more steadily using a flat-sided trash can or bucket than a rounded one. Or you may want to set up two box fans, one behind the other, to increase the range of air speeds (you can set both fans on low speed, one on low and one on medium, and so on). Once you’ve set your containers in the right positions, you may find that you need to winnow the contents of your seed-catching container a second time to clear away chaff to your satisfaction.
You may find some seed mixed in with the chaff in the second container. If so, compare it with the seed in the first container. Look for size or color differences. The lighter seed may not be as vigorous or have as high a germination percentage, but it’s probably not 100 percent nonviable. If you have chickens, you can feed the light seed to your chickens, or you can simply scatter it on a vacant garden bed where whatever sprouts can serve as a temporary green mulch.
If most of the chaff ends up in the first container with the seed, the air current was too gentle. Put everything from that container back in your pouring vessel, turn up the fan a notch, and try again.
At a winnowing station, pour seeds and chaff through a gentle stream of moving air to separate the two components. One container catches the heavy, viable seed. The other catches light, immature seed and chaff.
Using screens to separate seed and chaff is a less playful method, but it works quite well. Some seed companies and farm and garden supply companies offer screens specifically designed for screening seed. You can also experiment with making your own using pieces of window screening or hardware cloth.
To use this method, pour seed and chaff on a screen and rub it lightly with your hand. The principle is simple: Particles smaller than the screen openings will pass through, and particles larger than the openings will remain on the surface of the screen. You can work with a pair of stacked screens, too, putting a screen with large holes on top of a screen with small holes. Big pieces of chaff will get stuck on top of the upper screen while seed and small chaff will pass through. The second screen will catch the seeds, but the small chaff again will pass through, leaving the seed in the middle of the screen “sandwich.”
Collect or make screens with various sizes of openings so you can clean both large-seeded and small-seeded crops.
Carving a jack-o’-lantern is a pleasure, but scooping out the seeds and stringy pulp from the pumpkin in preparation can be a sticky mess. The pulp clings to your fingers and everything it touches. It’s important to clean off that sticky material (technically called “endocarp”) before you dry and store seeds.
To clean “wet” seeds from the squash family, you can simply put the seeds in a colander and rinse them with a spray of water until the sticky, slimy feeling is gone. Or you can put seeds in a bowl, add water, stir, and pour off the water, repeating this many times.
To clean wet seeds from tomatoes, you need to do some additional work. The gelatinous substance surrounding tomato seeds isn’t as sticky as some squash pulp, but it contains natural substances that inhibit seed germination. This is a smart idea on nature’s part, because the moist, warm conditions inside a tomato fruit are very favorable for seed germination. Without the inhibitors present, seeds might germinate inside the fruit while it’s still attached to the plant. There’s no future in that! The natural germination inhibitors are problematic, however, when you want to germinate the tomato seeds you’ve carefully harvested.
There’s an easy way to get rid of the germination inhibitor using a process that imitates what would happen in nature. When a tomato fruit drops off the plant onto the soil and is left there to sit, it rots. As it rots it ferments, and during fermentation the germination inhibitors are chemically changed so they’re no longer active. The tomato fruit rots away to nothing, and the now-uninhibited tomato seeds are released onto the soil surface, where they can germinate when conditions are right.
The process of cleaning tomato seeds (shown here) simply sets up conditions to allow fermentation to occur and break down the germination inhibitor.
Some other types of seeds benefit from fermentation, too, such as cucumbers and eggplant. Squash seeds also benefit, even though there’s no germination inhibitor in the pulp that surrounds squash seeds.
Cleaned seed will dry well in an airy place at normal room temperature. To encourage the drying process, set up a small fan to blow at low speed over the seed. It usually takes about 2 weeks for seeds to reach the desired dryness for storage.
To test whether seed is dry enough to store, simply put one end of the seed, such as a squash seed, between your teeth and bend it with your fingers. Properly dry seed will snap in two. For fat seeds such as beans, put the seed on a hard, flat surface and hit the seed with a hammer. Dry seed will shatter into pieces.
While you can try drying seed in a food dehydrator, it’s risky. Monitor the temperature carefully. If seeds are exposed to temperatures higher than about 85°F (29°C), they can become damaged and less able to germinate.
An easy and convenient way to store your dry seeds is to package them in paper envelopes. Coin envelopes, measuring about 2 inches by 3 inches, work well; they’re available at discount and office-supply stores. Always label every envelope with the crop and variety name and the month and year of seed harvest. If you’ve tested the seed, include the date of the test and the germination rate, too.
In general, vegetable and flower seeds will stay viable longest when stored in cool, dry conditions. How cool is “cool”? For seed storage, it’s probably cooler than you’ll keep your house during the winter. And “dry” is generally drier than you might want your house to be during the winter, so storing packaged seeds on a countertop or even inside a drawer in your kitchen isn’t a good idea.
Temperature and humidity requirements. As a rule of thumb, seeds do best when the sum of the air temperature and relative humidity is less than 100. For example, let’s say your kitchen is about 65°F (18°C) during the winter and the humidity is about 55 percent. When you add the temperature and humidity together (65 + 55), you get a total of 120, which is higher than optimum. In this case, you need to either lower the temperature of your kitchen to 45°F (7°C) — brrr! — or lower the relative humidity to 35 percent. If you live in a desert climate, that might be possible, but you may not be comfortable in such dry air.
Places in the home. Instead of adjusting the conditions of your living space, look for existing cool spots in your house. Buy a small thermometer or two, and start monitoring temperatures around your house. You may find an unheated bedroom or closet or a place underneath a bed that will work. A root cellar could also work, but some root cellars have very high humidity — as high as 90 percent — so check your cellar’s humidity level first. Keep in mind, too, that mice love to eat seeds. Store your seeds in a sturdy plastic box with a tight seal or in a metal canister rather than a cardboard box, unless you’re sure that no mice are ever part of your household.
Glass jars. In a humid climate, your best bet may be to store your packaged seeds in glass jars with some packets of silica gel (keep the gel separated from the seeds). The silica gel will absorb moisture from the air. When it turns from blue to pink, it has absorbed all of the moisture and should be replaced with fresh gel.
Refrigeration. A refrigerator is a good place to store seeds, as long as you seal your packaged seeds in airtight containers, such as tightly closed glass jars. Add a small packet of silica gel to the jar for extra insurance. Seeds can survive freezing, so you may also keep them in the freezer. If you do store your seeds in a refrigerator or freezer, let the container of seeds sit unopened for a while after you remove it to add or take out seed packets. Otherwise, condensation may quickly form on the inside of the cold glass, which will increase the humidity in the container when you seal it back up.
You’ve stored your dried seeds over the winter in a cool, dry place. Now it’s spring, and you want to start planting them. Before you do, it’s a smart idea to run a germination test. Commercial seed growers conduct germination tests on all their seeds, and on many seed packets you’ll find a notation of when that lot of seed was last tested and what the germination rate was. Seed companies are continually testing their stocks of stored seeds to be sure that germination rates remain high.
Your homegrown seeds don’t come with an automatic guarantee. Even if you followed all the instructions for growing, harvesting, cleaning, drying, and storing seed, it’s possible that the seed won’t have much viability (the ability to germinate) or vigor (the ability to grow robustly).
It’s easy to conduct a germination test to check your seeds’ viability and vigor. Simply take a small sample of seed, place it in conditions that are highly favorable for germination, then observe it. You’re looking to see how many seeds germinate, how quickly they germinate, and what the tiny seedlings look like.
One common method is to put seeds on a damp paper towel, roll up the towel, and put it in a plastic bag to keep it moist. Shown here is a variation on that theme that allows you to keep track of several varieties at once and keep notes on a handy chart. Always label, label, label, as you set up the test!
How long you will need to run the test depends on which crops you’re testing. For example, lettuce and radishes are fast germinators — you may even see results in 24 hours — but pepper seeds can be very slow, taking up to a month to germinate. Keep in mind that optimum germination temperature varies by crop, too. Some seeds won’t germinate well in cool conditions.
Your germination test will give you a percentage germination rate, but that’s not the only measure of success.
The real test of your seed-saving efforts happens when you plant your saved seeds in the garden and watch the results. You’re bound to have successes, occasional disappointments, and surprises!
Keep in mind that even “stable” open-pollinated varieties have some genetic diversity. Watch for variations. You may discover something fun, such as a flower that is a different color from its “siblings,” or something very useful, such as a plant that thrives even when all its neighbors are wilting in summer heat or turning sickly from disease. This is a unique opportunity to select the qualities that strike you as beautiful or interesting, or to develop a strain of a crop that will be superproductive in your garden. It’s the best part of the adventure of seed saving.