Breeding Your Own Squash

By Carol Deppe, June 23, 2008

The reasons to save your own seed are myriad and range from the practical to the profound. You can fine-tune established varieties; you can also take advantage of genetic accidents to create new varieties if you know how to save seed. Last year, for example, I saw one squash plant in perhaps a hundred that was resistant to powdery mildew. That fungal disease usually comes after the first fall rains and ends the growing season in my region. Resistant varieties could be very useful, so I saved seeds from the resistant plant. Perhaps I can use it to develop new powdery mildew-resistant varieties. Many new varieties got their start when some gardener or farmer simply noticed something that was different and special--and saved the seed. Depending on your preferences and predilections, seed saving can serve many other purposes.

Reasons to Save Seed

To grow a unique variety, you often have to get seed when and where it's available, then maintain the variety yourself. If you know how to save seed, you'll always have it.

Many spectacularly flavorful, unique varieties of pumpkin and squash are not readily available commercially, either as fruits or seed. For example, one of my favorite winter squashes is 'Blue Banana'. This squash has a flavor so unlike that of other squashes that it's like an entirely different vegetable. However, the seed is available from only one seed company, Seeds Blum, and from a few members of the Seed Savers Exchange.

Saving your own seed also means independence. It lets you make your own choices rather than being subject to random food fads or other people's choices and preferences.

You can plant what, when, and how you like. I like to produce my own seed for varieties that are readily available commercially. My own seed is usually bigger, fatter, and more vigorous. I can plant it earlier than commercial seed. I also have much more of it, so I don't have to skimp. I can sow generously and then thin, instead of sowing thinly, then having gaps that have to be replanted later and less optimally. And with my own seed, the price is always right.

When you save seed, you become a plant breeder. You choose which characteristics to perpetuate. You select for characteristics that are important to you, such as plants that suit your taste preferences, growing conditions, and region. After you have saved seed of a variety for a few years, you'll have a variety that is somewhat different from anyone else's, and usually better adapted to your growing conditions.

When you save seed you deepen your relationship with plants and gardening. Gardeners care about their direct relationship with soil, plants, and food. To grow plants from seed bought from others is one level of relationship. To save seed to grow new plants goes to a deeper level. It is fulfillment and continuity--plants and people maintaining each other, nurturing each other--in a continuous cycle.

Saving seeds of squash and pumpkin is unusually easy. The flowers are big, dramatic, and easy to handle. Hand pollination is fast and simple. And from each hand-pollinated fruit you get lots of seeds--hundreds of them, sometimes several ounces' worth.

To become an expert squash and pumpkin seed saver, you have to know three basic techniques: selection, hand pollination, and seed processing.

C. pepo, a delicata type

Family relations: squashes and pumpkins

Squashes, pumpkins, and vegetable marrows belong to one of four species of Cucurbita:

C. pepo includes most of the summer squashes, nearly all the acorn and delicata types of winter squash, and many classic pumpkins, such as 'Small Sugar';

C. maxima includes many of the finest long-storing winter squashes, such as 'Sweet Meat', 'Green Hokkaido', and 'Red Kuri' (three of my favorites), all the Hubbards and banana types, and most of the giant pumpkins;

C. moschata includes 'Tahitian Melon Squash', 'White Rind Sugar', and all the butternut types; and

C. mixta (sometimes called C. argyrosperma) includes 'Campeche', 'White Cushaw', 'Silver Seed', and others.

Incidentally, there's little rhyme or reason why a cucurbit variety is called a squash, a pumpkin, or a vegetable marrow. For example, you can legitimately call any squash a pumpkin, and vice versa. When looking for a specific variety in a seed catalog, however, look under both squash and pumpkin.

Squashes and pumpkins are monoecious, meaning each plant has separate male and female flowers. The plants are primarily pollinated by various kinds of bees. Different species do not cross spontaneously, with the possible exception of C. moschata and C. mixta. So if you grow only one variety of C. pepo, one of C. maxima, and one of C. moschata, and you have no squash-growing neighbors closer than about 1/2 mile, you can save your own seed without having to do hand pollination. Very few of us live more than 1/2 mile from gardening neighbors, however. And as we learn seed saving, we want to grow more varieties, not fewer, because so many more possibilities exist; so for most of us, seed saving requires learning to pollinate by hand.

Save your own seeds and you'll have many more to plant next spring

How to Save Your Own Seed

You can save seed from any standard or heirloom variety. You cannot however, save seed from F1 hybrid varieties, because they don't breed true (offspring will not necessarily resemble the parents).

Selection. The first technique for successful hand pollination and seed saving is selection. This is the most basic plant breeding method. To select is to choose which genes and characteristics to perpetuate. We do it by saving seed from the best plants. Superior plants are more likely to produce superior offspring. Which are best? How do we decide? Here are some basic guidelines to consider when planning your garden with seed saving in mind.

Grow several plants of any variety you plan to save seed from. There are two reasons. First, if you have only one or two plants, it may be difficult or even impossible to find a female flower and a male flower at the right stage for hand-pollinating simultaneously. With three or more plants, it's usually easy. Second, with several plants, you can save seed from the best. With just one or two plants, you end up having to save from all the plants, not just the best.

Plant plenty of seed if possible. I like to plant six seeds in a hill and thin to the one or two that germinate and grow most vigorously. This way, I automatically select for lines that germinate and grow well under my growing conditions.

Examine the plants before you start hand pollination. Don't use male or female buds from plants that are small, stunted, off-type, or otherwise obviously inferior. Remember that both parents (the pollen-donating male plant and the bud-carrying female one) matter.

Keep a record of which plants the male and female flowers for different hand pollinations come from. Often individual plants of a single variety are different enough to matter. In addition, varieties sometimes contain a few off-types. If one plant turns out to be something other than what it should have been, you will want to know, for example, which hand pollination it donated the pollen for.

Both self- and cross-pollinations have advantages. That is, you can use pollen from the same plant or a different plant. Self-pollinating means a loss of genetic heterogeneity in the next generation, which is an advantage if the individual plant turns out to be exceptionally good. Its seed will produce plants that are more uniform and more like their superior parent than the seed you started with. On the other hand, pollinating a female flower with pollen from a different plant of the same variety does a better job of maintaining all the genetic variability present in the variety so that it is there for you to select from in the future. Some species and varieties lose vigor if they are inbred (self-pollinated generation after generation), a phenomenon called--inbreeding depression. But it doesn't seriously affect squashes and pumpkins.

The second stage of selection comes at the end of the season, when the fruits are mature or nearly mature, but before harvest. Evaluate the individual plants, and make notes about early maturity, yield, and other important characteristics. It is important to consider the whole plant, not just the individual fruit. Don't be fooled into being impressed by the biggest fruit, for example, if the plant had only one fruit but is supposed to have several.

The proof is in the eating. The final stage of evaluation comes when you eat the fruits. I make notes about flavor (if different from what I expect), and how thick the flesh is.

If I end up with many hand pollinations that seem equivalent, I may pool the cleaned seed. Often, however, my various records indicate that one hand-pollinated fruit represents the "best" parents. I set that seed aside for planting the next year.

How to Hand-Pollinate

Squash and pumpkin plants have separate male and female flowers on the same plant. The female flower buds have a baby squash at the base; the male flower buds don't. The baby squash reflects the shape, and sometimes the color of squash that the plant will produce.

Tape-ready buds have a yellowish color lacking in younger buds and often gape at the tip. Locate buds that are at the right stage, and tape the chosen male and female flower buds shut late in the afternoon or evening before they are due to open for the first time. This is necessary to exclude pollinating insects, which are unlikely to consult you about the kind of pollen you want on each flower. Don't tape the buds any earlier, because they grow quite a bit in that last day, and they would rip open as they grow against the restricting tape.

Plants usually produce several male buds early in the flowering season, before they produce any female buds. Don't get discouraged if you can't tell whether buds are male or female when the plants have just started flowering; there probably aren't any female buds yet. Keep watching.

Next, mark the positions of the taped buds to find them quickly the next morning. I use bamboo stakes with tags of colorful surveyor's tape. (Use different colors of tape to mark male and female buds.)

Hand pollinations are most likely to succeed when they are done on one of the first few female flower buds the plant produces. In addition, fruits often drop off early in development if an earlier fruit is growing on the same vine. So, to maximize the success rate for hand pollinations, do them early in the flowering season. If a fruit has already set on the vine before you hand-pollinate, remove it to eliminate the competition. I usually do at least six hand pollinations (using different plants or combinations of plants) for each variety I want to save seed from.

My success rate with this method is better than 90 percent. Nearly every cross succeeds. My success rate on somewhat later flower buds, and with no removal of competing fruits, is only about 20 percent.

The right time for hand pollination is in the morning, as soon as possible after the male flowers release their pollen (so that it is soft and loose and fluffy, and ready to come off the anthers at the slightest touch, not moist and sticking tightly to the anthers). The exact timing varies with weather conditions, being later if the morning is colder or the plants are wetter. In most areas, 7 to 11AM is the useful period. You can examine untaped flowers to see whether they have released their pollen yet.

When you're ready to pollinate, pick the taped male bud, and carefully tear the petals off, exposing the pollen-bearing anther. Tear off the taped end of the female bud, and daub the pollen onto the stigma, using the stripped male flower as a pollen-transfer stick.

If many bees are active in your squash or pumpkin patch, watch them and work quickly once the buds are exposed. Sometimes, bumblebees will dive into a bud you're holding and rip off all the pollen right before your eyes.

Use all the pollen from one male bud to pollinate just one female flower. (Various books claim that you can use pollen from a male bud to cover two or three female buds, but I've found that this lowers the success rate dramatically.) Finish pollinations by late morning. Later hand pollinations are less likely to succeed. Also, by late morning, the pollen has dropped off the anthers inside the male flower buds and is trapped in and stuck to the base of the petals, where it is much more difficult to recover and work with.

Harvesting Seeds

When your squash and pumpkins reach full maturity, it's time to harvest the seeds you want to save. Winter squash and pumpkins are ordinarily picked from the vine at full maturity, so harvesting them for seed saving involves nothing special. Summer squash, however, are usually eaten when immature. To save the seed of a summer squash, you must allow it to grow to full maturity, which is long past the best time for eating it.

The seed of squash and pumpkins continues to ripen for about three weeks after you've harvested the fruit. For seeds of maximum plumpness, vigor, and viability, wait at least three weeks after harvest before cutting the fruit open and cleaning the seeds. You can remove and clean the seed up to several months later if you wish.

Cleaning. I use two somewhat different methods, depending on whether I am saving seed from just one fruit or from many of one type in a single lot. To process the seeds of several fruits of one type (or a whole field's worth) at once, I use a scaled-down version of commercial processing involving a fermentation step (see "Processing Big Batches of Seed," below). Usually I save seed from only one squash or pumpkin at a time, however. In that case, a simple washing procedure produces beautiful, clean, loose seed.

Open the fruit and remove the seeds and attached debris. (At this point, you can cut up the flesh, pop the chunks into the oven or microwave, and cook them up.) Put the seeds and debris in a big bowl with at least 20 times as much water as seeds. Work the seeds and debris with your hands to free the seeds. (If the debris and seeds are fairly dry, you may need to let them soak for 5 minutes or so before working them.) Fresh seeds float, but most of the debris is slightly denser than water, so it sinks. Scoop the seeds off the surface of the water into another container, and pour out the debris-containing water. Repeat the process if necessary to eliminate all the large chunks of debris.

Next, put the seeds in a wire strainer, and swish them around gently to scrape and further clean them by gently rubbing them against the strainer. Then clean off the fine debris with a stream of water through the strainer.

Drying. There are two tricks to drying seed. The first is to dry at just the right speed. You want to dry it fast enough, especially initially, so that the seed doesn't have a chance to absorb moisture from the washing water and begin to germinate, losing viability. (As long as the seed is in the fruit, germination inhibitors prevent germination. As soon as the seed is washed, however, it becomes much more vulnerable.) On the other hand, seed that dries too quickly cracks and also loses viability.

The second trick is to rustle, fluff, and separate the seeds at a certain stage in the drying process so that they become loose and separate and don't stick together in big clumps.

I usually spread seeds for drying in a single layer on a screened tray in a food dehydrator and dry them for an hour or two at 95oF. If you don't have a dehydrator, you can leave small amounts of seeds in the strainer and set it in front of a fan indoors for 2 or 3 hours for the initial drying. For larger amounts, use a window screen or piece of hardware cloth and a fan indoors. You can also dry seeds on trays. But whatever you do, don't dry the seeds on paper, cardboard, or cloth because the seeds will stick to those materials.

You can also dry seeds in a shady place outdoors if the weather is warm and dry. Keep a close eye on the seed, however, to guard it from birds, squirrels, and other seed-coveting critters.

The first stage of drying is over when the surface of the seeds is dry and they stick to each other and to the screen, but not too tightly. At this stage, I "rustle up" the seeds. I rub my gloved hand around the dehydrator tray, strainer, or screen to separate the seeds from the surface and from each other. If the seeds dry completely without this rustling-up step, they stick very tightly and are hard to separate without damaging them.

After that step, I spread the seeds in a single layer in a tray, plate, or other shallow container and allow them to finish drying a few days or more without further attention.

A seed is completely dry when its covering snaps when broken in two. If it flexes or bends, it isn't dry. Transfer fully dried seed to envelopes, jars, or other containers for storage.

Storing. If stored in a cool, dry place, seed will keep for six years or more. It will keep even longer in glass jars stored in the freezer.

If you freeze seed, remove the jar from the freezer a day or more before opening the jar so the seed can come up to room temperature slowly and the main supply of seed does not become coated with condensation.

Processing Big Batches of Seed

To process several squash or pumpkins (or a whole field full) of one type, I suggest this fermentation method developed by Alan Kapuler, research director at Seeds of Change:

Put seeds, debris, and water into 5-gallon buckets, and set them aside for one to three days of fermentation. Sometime during the first day or so, swirl the seeds around with your hands to separate seeds and debris. Then, separate the floating seeds off into buckets with more water. Wait one to three days until the seeds sink. The good, vigorous seeds absorb water and sink. Inferior seed and empty seed husks don't sink.

Check the seeds daily to catch them on the day they go from floating to sinking. Collect the sinking seeds, rinse them, and put them on dehydrator trays. Dry them for eight hours at 95° F. (Stop drying them at the appropriate point, and "rustle up" the seeds to unstick them. See text above.)

A disadvantage of this fermentation method is that it's critical to dry the seeds quickly initially, because they've been allowed to absorb some water. You need a dehydrator. This method requires much less hand working than the simple washing method, though, because part of the work of separating seeds and debris is achieved by fermentation instead of hand labor. An additional advantage is that the poor quality seed separates out for easy disposal.

Carol Deppe, Ph.D., writes, gardens, and breeds vegetables in Corvallis, Oregon. She's the author of Breed Your Own Vegetable Varieties: The Gardener's and Farmer's Guide to Plant Breeding and Seed Saving (Chelsea Green, December 2000; $28).

Photography by National Gardening Association.

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