By Jim McCausland, Sunset Magazine

In his book Gardening When it Counts, Steve Solomon writes about what makes a great seed company. He should know: he started one (Territorial Seed) before moving to Tasmania, where he grows most of the vegetables he eats.

Solomon puts a lot of stock in companies that conduct their own germination tests (these show what percentage of the seed is viable) and that hold field trials for everything they sell. "For real, believable, and accurate information," writes Solomon, "you have to do trials." The alternative is to simply buy and repackage seeds—but if you haven't grown them, you don't really know them.

Organic field trials reveal much. They confirm germination tests, demonstrate regional adaptability, show which varieties resist diseases and insects, and reveal size and quality of plants. Solomon points out that heirloom varieties grown by a network of collaborating amateurs "often become irregular, inbred, weak." That shows up in trials, and can lead the grower to search for better sources or drop the line. And "only your own variety trial can reveal what tastes good." When produce is ripe, he starts by trying every variety raw (think not just tomatoes and peas—yum—but potatoes and pumpkins!). Those that don't make it over that hurdle never make it to kitchen trials.

Solomon has discussed these things with seed sellers on several continents. Here are his picks of the best seed sellers in the United States.

For both short-season and moderate climates, he likes Johnny's Selected Seeds and Stokes Seeds. For moderate climates only, he adds Harris Seeds and Southern Exposure Seed Exchange. For warm climates, he likes Park Seed Company. And for gardening in maritime climates (like the Pacific Northwest), he recommends Territorial Seed Company.

I've bought and grown seed from all of them, and second his recommendations. Thursday, I'll add a few favored by Sharon and myself.