Considering all of those seed catalogs that come in the mail over the winter, each offering hundreds of vegetable varieties, why would a gardener bother to collect seeds from the garden to start next year’s crop of tomatoes, beans, cucumbers or squash? Why undertake the effort of harvesting, cleaning, drying, and storing your own seed? There are two good reasons.

Perhaps while working in the garden you notice a single plant that stands out as being better than the rest – bearing larger or earlier fruits, growing taller, or suffering less from disease. It seems obvious that this plant is better adapted to your garden, to your local growing conditions. Over a period of years, consistent selection of seeds from such an outstanding plant (particularly if the plant is open pollinated, not a hybrid) can produce an improved strain that is better suited to your garden.

Or perhaps you have inherited an heirloom vegetable variety that your great grandfather grew in his garden, the seeds passed from generation to generation. You want to grow it not only because you recognize it as unique in flavor or regional adaptability, but because you understand the importance of conserving plants that can contribute vitally needed or desirable characteristics to the species’ gene pool. Your garden becomes a link in the chain of sustaining genetic diversity.

The first step in saving seed of any vegetable variety is learning how each vegetable plant species is pollinated, knowledge that is necessary to ensure the purity of saved seed. Open-pollinated species (nonhybrids) are of two types: self-pollinated and cross-pollinated. Varieties of a self-pollinating species, such as tomato, can be planted anywhere in the garden, but each variety of a cross-pollinating species, i.e. species such as corn that depend on wind or insects to move pollen from a flower on one plant to the flower of another plant, must be grown isolated from other varieties of the same species. (See sidebar for isolation distances for some cross pollinators.)

When saving seed of heirloom varieties, you also must maintain the variety’s genetic vigor. This cannot be done by collecting the seed from one or two fruits. Because desirable genetic traits are concentrated in individual plants of self-pollinators such as tomato, collecting seed from as few as six to 10 plants is adequate. However, desirable traits are distributed among many plants in cross-pollinators and saving the seed from a minimum of 20 to 30 plants is required for most varieties. For corn, saving seed from a minimum of 200 plants is advised to ensure a complete genetic picture.

Finally, it is important to understand the botanical relationships between some of our common garden varieties. For example, squash, pumpkins, watermelons, cantaloupes and cucumbers, all members of the cucurbit family, will cross-pollinate within their own species. Thus it is important to know that the species Cucurbita pepo includes pumpkins, all summer squashes (zucchini, scallop, crookneck, etc.), acorn squash, spaghetti squash and small gourds. All of these can cross and thus must be grown in isolation by the seed saver. The species C. maxima includes the long-keeping winter squashes (hubbard, buttercup, turban, banana, and delicata); each of these should be isolated from each other as well.

Next week: collecting and storing seed.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to reesermanley@shead.org. Include name, address and telephone number.

The following tips for seed savers were taken from a recent special edition of The Avant Gardener, a very informative monthly publication for gardeners (Box 489, New York, N.Y. 10028).

Beans: Common beans are mainly self-pollinating, but limas and runner beans are insect-pollinating and thus should be separated by at least a mile.

Corn: Wind pollinated; varieties need separation by at least a mile.

Cucumbers: Insect pollinated; varieties need separation by at least a half mile.

Melons: Except for watermelons, all melons will cross pollinate with one another, so separate varieties by at least half a mile.

Peppers: Separate varieties by at least 500 feet.

Squash: This is a confusing group that consists of several insect-pollinated species. Keep varieties of the same species isolated from each other by at least a mile.

Tomatoes: A favorite among beginning seed savers, the majority of tomato varieties are self-pollinating. To get the fullest range of genes from each variety, combine the seed of at least three plants.