Lettuce is a cool season green. It even germinates better in cool soil. You will want to start planting it a few weeks before your last frost.Then spread out several more sowings before the heat of summer. Resume planting when your heat breaks to get a long fall harvest. Lettuce originated in Egypt where it grew wild. The Romans loved salads. At that time the milky core of lettuces had narcotic properties which were later bred out.
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