Cool-season crops such as lettuce, potatoes, peas, cauliflower and onions actually prefer the cool, moist conditions of spring. With the extended mild winter, coupled with unseasonably warm conditions just at winter's end, our cool-season crops may be in fast-forward mode!
By March 13, soil temperatures under bare ground have already reached the upper 40s to mid 50s F in northern Indiana and in the 60s in southern Indiana. These temperatures are in the optimum range for germination of most cool-season crops and are nearly a month ahead of last year's.
But, especially given the mild conditions, gardeners need to remind themselves to allow soil to dry sufficiently before working to avoid soil compaction. Working wet soil tends to form hard clods that last all season. To quickly "test" the soil for workability, squeeze a hand full. If the soil crumbles easily between your fingers, it is dry enough to work. If the soil forms a muddy ball, then it's best to wait until the soil dries a bit more.
When ready, work the ground to a depth of at least 6 inches, using either a shovel or a mechanical tiller. This is a good opportunity to work in fertilizer to maintain your garden's nutrient pool and organic matter to improve soil structure. It's best to have at least one soil test, especially for a new garden, so you'll know the basic needs of your particular soil. Soil testing is also recommended for established gardens at least every three years or so. Such gardens often have sufficient phosphorus and potassium levels, so you don't want to needlessly add excess.
Many cool-season crops are best 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. A general rule of thumb is that the depth of planting should be about 1-1 1/2 times the size of the seed. When in doubt, check the seed packet for the proper planting depth and spacing for that particular vegetable.
If your soil tends to be heavy or compacted, or forms a hard crust, try placing a light mulch over the seeds as you plant them. A thin layer of vermiculite, finished compost or chopped grass clippings (free from weed-killer) will 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. This group includes cabbage, cauliflower, broccoli and Brussels sprouts. Transplants should be set at the same depth in which they were grown. If planted too deep, their roots may be too cold and starved for oxygen. Don't forget to water the transplants as soon as possible after planting. Young transplants can dry out very quickly, especially if weather is sunny, warm and windy.
Potatoes are unusual in that they are started from the tubers of last year's crop and are called seed potatoes. These tubers are modified stems that grow underground. The eyes on the potato tuber are vegetative buds, which will produce new stems and leaves. In turn, the new stems will grow new roots. Cut the seed potatoes into pieces, making sure that each piece has at least one healthy eye (bud). Plant the pieces about 4 inches deep and cover with soil.
For more information on spring gardening, check out the Purdue Extension's Home Gardener's Guide at www.hort.purdue.edu/ext/HO-32.pdf.