Seed saving basics: keep the plants that do well for you

Why save seed

A seed carries a memory of where it grew. Save seed from the plants that did best in your garden, year after year, and you're quietly breeding a variety for your own soil and climate.

It starts with knowing which seeds will come true. Seed Savers Exchange explains that open-pollinated varieties produce offspring like the parent, as long as they only cross with their own variety. Hybrids are crosses of two different varieties, and as University of Minnesota Extension notes, seed saved from a hybrid won't reliably look like the plant it came from.

Heirlooms are open-pollinated varieties with a documented history of being passed down. Seed Savers Exchange doesn't set a strict age cutoff, though it calls varieties sold before 1950 "historic."

Start with the easy ones

Some crops make seed saving almost foolproof. Seed Savers Exchange notes that tomatoes, peas, and beans mostly pollinate themselves and rarely cross, and University of Minnesota Extension adds peppers to the beginner list. Squash, cucumbers, corn, and spinach are much more likely to cross with neighbors, so save those later, once you've got the hang of it.

Keep varieties apart

If two varieties of a crossing crop grow near each other, their seed can be a mix. Seed Savers Exchange's crop chart gives minimum isolation distances for home gardeners, and warns they prevent crossing most of the time, not always:

• Beans, lettuce, peas, and most modern tomatoes: 10 feet.
• Potato-leaf tomatoes: 40 feet.
• Sweet peppers: 160 feet. Hot peppers: 800 feet.
• Squash, cucumbers, melons, corn, cabbage-family crops, carrots, and onions: 1,600 feet.
• Beets, chard, and spinach: 3,200 feet.

Dry seed and wet seed

Seed Savers Exchange sorts crops into two groups. Dry-seeded crops like beans and lettuce are left on the plant until the seed is dry, then harvested. Wet-seeded crops like tomatoes, squash, and watermelon are picked when the fruit and seed are mature, and the seed is cleaned out.

Tomato seed sits in a gel that needs to ferment off. Seed Savers Exchange suggests letting it sit one to three days in a cool place; University of Minnesota Extension describes a jar of seeds and water, stirred twice a day, until the good seed sinks, usually within about five days. Then rinse and dry.

Dry it, then keep it cool

Seed is dry enough to store when it snaps or shatters instead of bending, according to Seed Savers Exchange. Keep it airtight, cool, and dark.

Illinois Extension gives a handy rule: the storage temperature in °F plus the relative humidity in percent should add up to less than 100. University of Minnesota Extension suggests sealed glass jars with a desiccant, such as silica gel or a spoonful or two of powdered milk.

Test before you sow

Seeds lose vigor over time, at different rates. Colorado State University Extension lists rough averages: lettuce, onion, and parsnip about 1 year; sweet corn and pepper about 2; bean, carrot, pea, and spinach about 3; beet, squash, and tomato about 4; cucumber about 5. Other charts disagree, so treat these as estimates.

A quick test tells you for sure. Illinois Extension suggests rolling about 10 seeds in a damp paper towel, sealing it in a bag at around 70°F, and checking over 7 to 10 days. If most sprout, plant as usual. If 70 to 90% sprout, sow more thickly. If fewer than about half sprout, it's time for fresh seed.

The legal fine print

Most garden seed is free to save. Some varieties are protected. The USDA explains that Plant Variety Protection certificates last 20 years, or 25 for trees and vines, and that home gardeners may save seed of legally purchased protected varieties for their own planting. Some varieties also carry patents or contract terms, so read the seed packet before you save and share.