Knowing when to plant your vegetable garden ensures a healthy growth cycle and harvest no matter where you live. Different areas have much different planting times. Michigan gardeners, for example, have cold winters and sometimes late springs, depending on which part of the state they live in. Timing for warm-season, cool-season and tender crops varies greatly and relies heavily on soil temperature and frost dates.
Warm- Vs Cool-Season Crops
Not all vegetable crops require the same season or temperatures to grow vigorously, nor are they all equally tolerant of frost, shade, heat or snow. Warm-season crops are those that grow best during the warmer parts of the season. These include sweet corn (Zea mays var. saccharata), cucumbers (Cucumis sativa), tomatoes (Solanum lycopersicum), peppers (Capsicum spp.) and melons (Cucumis melo); all of these are tender crops that are susceptible to frost damage or even death by frost. Cool-season vegetables, on the other hand, prefer the cooler temperatures of fall and spring. Many are frost-tolerant, some to temperatures as low as 20 degrees Fahrenheit. Onions (Allium sepa), peas (Pisum sativum), spinach (Spinacia oleracea), leafy lettuces (Lactuca sativa) and cole crops (Brassica oleracea) are all cool-season vegetables. Cole crops include kale, broccoli, cauliflower, kohlrabi and cabbage. Cool-season vegetables tend to bolt, become tough or woody or have otherwise adverse flavors or textures when grown in summer.
Many cool-season vegetables can handle planting times as early as the soil thaws and is workable, usually late March through early April in southern Michigan and three weeks later in the most northern parts. Tender, warm-season crops, however, require much warmer soil temperatures and must wait until the danger of frost has passed. Planting on Memorial Day is a good rule of thumb, but frost dangers occur frequently throughout much of Michigan in spring. If you plant around mid- to late May, keep an eye on the weather forecast and cover your seedlings or transplants if temperatures will fall below 40 degrees F.
Checking Soil Temperature
Checking the soil temperature helps ensure your ground is ready for various types of seeds. Different crops grow best at different soil temperatures. Purchase a soil thermometer from your local hardware store or garden center; you can also use any thermometer that has the capability of reading temperatures at different depths. Many tender warm-season crops require a soil temperature of between 64 and 75 degrees F, while tomatoes and corn grow well when planted at around 55 degrees F. Cold-tolerant crops will germinate and grow at a soil temperature of around 45 degrees F.
Days to Harvest
For fall planting, knowing the days to harvest, sometimes called days to maturity, of each crop will help you determine when to plant the seeds. The days to harvest is listed on each seed packet and determines how many days a seed takes to mature and produce harvest-ready fruit. For warm-season crops with short growing times, you can often plant twice during the summer. Subtract the days to harvest from your last average fall frost date to give you a planting date for frost-tender vegetables.