If you're planting a vegetable garden you'll want to pay close attention to frost and freeze dates to determine when to plant. This article gives an overview of how to determine when to plant and offers links to additional online resources for determining your frost and freeze dates.
Planting times for vegetables and other annual plants vary from species to species. In much of the United States the prime consideration is the date of the last spring frost/freeze. Many vegetables can be planted up to four weeks before the last frost, while others need to wait until a couple of weeks after the frost.
Another consideration is the date of the first fall frost/freeze. In northern latitudes, where summers can be short, the length of time some vegetable species take to reach maturity (most notably tomatoes and peppers) make it necessary to plant vegetable seeds indoors and then transplant the seedlings outside at the appropriate time.
Other vegetables and fruits, such as winter squashes and some melon varieties, seem to do better when planted as seeds directly where they are going to stay. With maturation times up to twelve weeks, it may be critical to get vegetable seeds planted as early as it is safe to do. If you have a short growing season, and wish to grow these crops, choose vegetable varieties that will reach maturity within a safe time period for your area.
My personal observation has been that vegetable seed crops planted at their earliest safe date are less likely to fall victim to insects than later plantings. If you have a small vegetable garden it's not too difficult to reseed if a surprise late frost damages a particular crop.
Many vegetable plants that are planted in the spring can be planted again towards the end of the season. Again it is important to know what date you can expect the first frost.
By understanding the times and length of frost free weather in your area you can have a better chance for success in your vegetable garden.
The National Climatic Data Center has a data sheet online that can be downloaded as a pdf file or viewed online. The data sheet contains frost/freeze information for over 3000 U.S. locations. The information is presented as a table, listed in alphabetical order by state and then selected towns within each state.
Be aware that this information is based on 29 years of data gathering from 1951 to 1980, and that they are statistical in nature and cannot unequivocally predict exact dates for any given locality in any given year.
Biodynamics and Phenology use astrological and natural occurrences to discern clues about the best time to plant and harvest vegetables. Native Americans and other earlier civilizations used similar techniques.
Most areas consist of microclimates that vary by elevation, exposure and proximity to large bodies of water. The Freeze/Frost Tables are a good reference point, but it makes sense to keep track of temperature and other factors in your particular vegetable garden location if you want to truly understand when it is actually the best time to plant vegetables.
Chip Phelan, a contributing editor for Organic Gardening Review, is an organic gardener living in Rhode Island. Organic Gardening Review is a resource center for organic gardening enthusiast and those interested in community sustainable agriculture.