Gardens are typically planted two weeks after the last frost date for the region, depending on the varieties of crops planted. Last frost dates for each hardiness zone can be determined using the USDA Plant Hardiness Zone Map.
As of 2014, the United States is divided into eight hardiness zones that each have a unique frost date. To determine the best time to plant a garden, locate your state or city on the USDA Hardiness Zone Map, and determine the corresponding last frost date for your hardiness zone. Most regions in the United States experience the last frost of winter in early to mid-spring. It is also necessary to determine the hardiness of the crops being planted to avoid planting gardens too early in the season.
For instance, cold-weather crops and frost-tolerant vegetables, such as cabbage, carrots and beets, are typically planted up to six weeks before the last frost date of the season. Tender vegetables, such as beans and corn, are planted on or after the frost date. Warm-weather vegetables, such as melons, should be planted approximately two weeks after the last expected frost date to ensure the crops are not damaged by cool weather.
Plants can be started in containers indoors four to six weeks before the final frost date and transferred to the garden at the recommended time. Information concerning the appropriate time to plant specific types of crops is found on seed packets.