If a cold-frame isn’t available to start early greens, wait until soil temperatures have warmed to 40 degrees F at a depth of 4 inches at 8 a.m. Soil temperatures recorded at the CSU campus weather station over the last five years show that soil typically reaches this temperature during the last few days of March. Daytime air temperatures that are consistently 40 degrees or more are also desirable. The list of cold tolerant vegetables includes broccoli, cabbage, kohlrabi, onions, lettuce, peas, radish, spinach and turnips.
If a winter cover crop of rye or Austrian winter pea was planted in the fall, it should be tilled in mechanically or turned under with a spade a month before planting or seeding new crops. Decomposing, turned under plant material (“green manure”) consumes soil oxygen and can create plant health problems if not tilled in ahead of time. This decomposition is necessary to achieve the benefits of planting the cover crop. These benefits include increasing soil fertility and building soil structure.