Friday, February 19, 2010

Seed Saving

By Nina Berryman

Seed saving is a fascinating, sometimes daunting, and often overlooked part of vegetable production. Most farmers and gardeners leave it up to the professionals, and are content to invest money instead of time and energy to get their supply of next year’s seed. Most of the time, I too fall under that description. While I have limited experience with seed saving, I am quite interested in the techniques, and hope to do more of it in my future. Here is a quick intro to the basics of seed saving to get you started, or at least pique your interest!

Seed saving is the process of saving seed from desirable plants in order to grow them again in following years. Creating new varieties is a different topic; what I’m writing about here is how to preserve existing varieties in your garden. What makes seed saving complicated? The seed you save from a plant will not necessarily produce new plants that look like the plant from which you collected it. Sometimes it does…but often it doesn’t. Therefore, the first step in seed saving is to understand how plants naturally reproduce, so you then know how to interfere to get your desired results. In other words, how do you interfere so that the seed you save DOES look like the plant from which you collected it?

Plants are pollinated three different ways: self pollination, insect pollination, and wind pollination. In order for a flower to be pollinated, pollen must reach the ovary of the plant. On some plants, the pollen and the ovary are part of the same flower (called a perfect flower) and they can self-fertilize on their own (for example beans).Other plants have pollen and ovaries on separate flowers (called imperfect flowers, where one flower is male and one is female). These plants require that either wind (in the case of corn) or insects (in the case of squash) move the pollen from a male flower to a female flower in order for the ovary to be fertilized.

When pollen from one type of plant fertilizes an ovary from another type of plant, you have hybridization. This can occur between different varieties (such as two varieties of peppers) as well as different sub species (such as broccoli and cabbage). Maintaining seed purity is important to ensure that the seed you save looks like the plant from which you are saving it. This is not a concern with plants that only self-fertilize. Plants that are wind pollinated or insect pollinated can be isolated a few different ways. One is by distance. Different plants require different isolation distances. This method can be hard for the backyard gardener who has neighbors in close proximity. Seed purity can also be maintained through time isolation, meaning different varieties are planted at different times in the season such that the time during which they are flowering does not overlap. This can be hard in climates that have short growing seasons. Seed purity of insect-pollinated plants can be maintained through mechanical isolation such as bagging or caging. In these cases you either tie a bag around the flower, or build a screened cage around the plant to prevent insects from cross-pollinating between different plant types. If you bag a flower, you need to then do the work of the insects yourself and hand-pollinate the flowers yourself (sometimes done with a q-tip). If you cage plants, you can introduce the necessary insect pollinators to that cage.

When selecting desirable plants it is important to observe the plant during the entire growing season and take note of different characteristics. Look at all parts of the plant, not just the fruit. Consider earliness, disease resistance, insect resistance, drought resistance, stockiness, uniformity, trueness to type, color, size, productivity, storage ability and of course, flavor. Be sure not to eat all the best looking plants and only leave the weakest ones for seed saving!

Population size is another important consideration for saving seed. The more plants from which you save seed, the greater the genetic diversity of your selection and the more robust your seed bank will be. This is particularly challenging for the backyard gardener who has limited space. The general rule of thumb is in order to have enough genetic diversity in you seeds, you should save seed from at least 20 self-pollinating plants or 100 cross-pollinating plants. Even with a large selection pool, genetic diversity can decline over the course of many years of seed saving from the same gene pool. When this happens new genetic material needs to be introduced to the plant population by planting seeds of the same variety but from a different source, such as a seed catalogue or a neighbor.

The next step in seed saving, after you have collected the seed, is cleaning. There is wet and different plants require different techniques. Wet processing is required for tomatoes. Many plants must first ferment (i.e. rot) so that microorganisms destroy seed-borne diseases. Then seeds should be separated from the pulp. This can be done by repeatedly putting the fermented mixture in water, stirring it, and letting bad seeds and pulp float to the top, and good seeds sink to the bottom. Then the good seeds must be patted dry and fully dried on a non-stick surface, like glass, ceramic or a cookie sheet, not paper, cloth or non-rigid plastic. While drying, do not expose the seeds to temperatures higher than 95 degrees Fahrenheit. Good places for drying include in a cold oven with the pilot light on and the door cracked open, or on top of the refrigerator.

Dry seed processing is used on seeds that have husks or pods. After the seeds have completely dried on the plant, remove the seed heads and crack open the husks or pods. Be sure not to apply so much pressure to the seed heads that you damage the seeds themselves. Winnowing is the process of separating the husks from the seeds, and can be done by pouring the seed mixture from one bucket to another in front of a fan on low. The slight breeze blows the light, unwanted husks away while the heavier, desirable seeds fall safely into the bucket below.

Now that you have your seeds, it is important to store them properly so they last from one year to the next. Heat, light and moisture must be kept to a minimum. Air tight containers such as glass canning jars with rubber seals are ideal. For long-term storage, put seeds in the freezer. Be sure the seeds are completely dry though, otherwise this will damage them.

It is useful to test the germination rate of seeds before planting them to make sure they are still viable and you are not wasting precious garden space. This can be done by placing at least 25 seeds between two moist paper towels, then placing the paper towel in an open plastic bag, so the seeds can breathe but moisture is retained. Place in a warm place and re-spray the paper towel to keep it moist. The area should be kept at a constant temperature, usually around 75 degrees F is best. The top of the refrigerator is usually a good place. Check the seeds daily, and remove sprouted seeds once a week, after counting them. Research the germination length for the seeds you are testing and after that length of time has passed, add up the number of seeds that germinated and divide by the original number of seeds on the paper towel. This will give you your germination rate.

I suggest trying to save seed from these vegetables: beans, peas, spinach, cilantro, fennel, lettuce, okra, tomatoes.

Source: Ashworth, Suzanne. Seed to Seed. Seed Savers Exchange Inc. Iowa. 2002

No comments:

Post a Comment