Start with dark green, stout transplants equally high and wide, preferably about 4 inches in each direction. (My step-by-step for growing your own includes many tricks; you can also shop locally for seedlings or by mail.)
Plan to grow a mix of heirlooms and hybrids for a little insurance: Heirlooms are beautiful, delicious and a critical part of our genetic heritage, but sometimes they lack the disease-resistance (often labeled VFN) of hybrids. I like to mix it up.
Remember that even with hybrids rated as having VFN resistance, the word “resistance” is the operative phrase. It means less-susceptible, not immune. There is no substitute for good cultural practices, whatever variety you begin with.
Identify a full-sun spot outdoors where your tomatoes will grow. Now pick another such spot, and preferably a third. You will need more than one area for tomatoes, since crop rotation is one of the key lines of defense against tomato various diseases that can overwinter in the soil. (No other Solanaceous cousins, no potatoes, eggplants, peppers or tomatillos, can go there in the off years, either.)
While your transplants shape up, prepare the soil: Start with a soil test, or at least a simple pH test. Tomatoes like a pH of about 6.5 (6.0-6.5 or so is fine). In acidic soils like mine, the addition of lime is recommended, at the rate of 5-10
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