Seed packets may hold some of the keys to successful planting times. Most of them have a chart, suggesting dates for sowing or a map of zones to guide you as you begin your spring planting. These are excellent starting points but often fail to take into considerations such things as micro-climates and seasonal fluctuations. The main item of concern is the date of the last frost in your region. Averages can be found here at Davesgarden.com, through your Extension office or you can do what I do, and wait until Mother's Day to sow your beds. Other factors include soil and ambient temperature, lighting and exposure, and average rainfall.

The Best Time

Extension offices are local and have the best information through Master Gardener's programs for a specific region. These offices take into account the region's special weather patterns for optimum guidance on planting times. Local experts know more than the average date of the last frost and are valuable resources for the best types of plants to grow in your region, some early starting varieties and tips on how to get gardening earlier. If you lack an Extension office near you you can pinpoint your own best sowing times with a soil thermometer. You can also encourage a micro-climate of your own where soil is warmer and some protection is available for those tender veggie babies.

The Right Soil

The best soil temperature for germination and growth will vary by variety of plant. Hardy plants can accept soil temperatures as low as 40 degrees Fahrenheit and the occasional light frost. Semi- hardy varieties prefer temperatures of 50 degrees or more and cannot withstand a chill. Warm season plants need soil temperatures above 60 and preferably warmer. The actual soil temperature for germination varies but on average soil needs to be 50 to 60 degrees Fahrenheit on average. Cucurbits and plants in the nightshade family germinate best at 60 or more. Of course, you can always get around the germination requirement by starting seeds indoors and planting them out after the last frost.
You can enhance your soil temperatures somewhat by using raised beds, solar soil covers, cloches, water walls greenhouses and hoop structures. Any of these may give you just a few extra degrees in increase to make growth and germination possible earlier. Deeply cultivated soils with plenty of added organic matter warm more quickly than compacted soils and enhance plant growth. A thick bed of mulch or leaves can also impact soil temperatures for a quicker growing season.

Going Lunar

Another way to get a jump start on the season is to use lunar planting charts. The Farmer's Almanac has an excellent and easy to use moon calendar which will give you a good idea of when and what to plant. The United States and Canada are divided into 4 regions. Once you find your region you can glean their best advice on vegetable types to plant in each month. Certain dates are thought to be more favorable due to astronomical conditions which promote better growth. It may sound like science fiction but this method has been used by farmer's for centuries.
Early varieties of vegetable hybrids are sold in their appropriate zones. Your garden center will carry the types of plant that are best for your region and will have advice on more cold tolerant species. For instance, Stupice and Glacier are two cold tolerant tomato plants that start producing within 55 to 60 days. That means short season gardeners can actually look forward to a bumper crop of these traditionally long season warm weather vegetables by planting them earlier and getting a harvest sooner. You still should start the plants indoors but you can plant them out a few weeks earlier than standard varieties with some protection.
Fortunately for even northern gardeners there are numerous plants that not only tolerate the cold but thrive in cooler climes. Early spring or late summer seeding will result in a plethora of veggies in early summer or fall. Some of the types to try are: leeks, rutabaga, broccoli, English peas, cabbage, collard, kale, kohlrabi, cauliflower, celery, beets, Swiss chard, most lettuces, carrots, turnip, and spinach. Plants that need to have warmer soil and cannot tolerate any frost might be: Beans, tomatoes, eggplant, summer squash, okra, melons, cucumber, corn and sweet potatoes. Start these indoors or from purchased transplants after all possibility of frost has passed.
Every zone is different and the Mother's Day rule is still best for any varieties that are not hardy but we can also reserve the date to simply honor our Mom's and use other planting guides for a more complete picture of plant tolerances and seasonal growth. Early season planting is possible if you know what types to grow and use some sneaky tips to enhance soil heat and protect young plants from possible chill damage. Happy planting!