By B. Rosie Lerner, Extension Consumer Horticulture Specialist Purdue University, West Lafayette, Indiana Some like it hot, but many vegetable crops are best adapted to cool soil and air temperatures. Cool-season crops, such as lettuce, spinach, potatoes, peas, onions, root crops and all members of the cabbage family actually prefer the cool, moist conditions of spring or fall to hot, dry summer weather. Many cool-season crops can be started by sowing seeds directly into garden soil. This group includes peas, carrots, beets, lettuce, spinach, radishes and turnips. Each crop has its own optimum planting instructions.
Most gardeners make the mistake of planting the seed too deep.
A general rule of thumb is that the depth of planting should be about one and a half times the size of the seed. When in doubt, most seed packets list the proper planting depth and spacing for that particular vegetable. If your soil tends to be heavy or form a hard crust, try placing a light mulch over the seeds as you plant them. Vermiculite, finished compost and chopped grass clippings all allow the young seedlings to come up easily after germination. Other cool-season vegetables are best transplanted to the garden to give them a head start on the growing season.