Tomato plants are tender, meaning that freezing temperatures damage the plants and fruits. Unless you are equipped to shelter plants out in your garden from frost, wait until the weather has warmed up in the spring before planting tomatoes outdoors. If you are transplanting tomatoes that have been grown indoors, help them acclimate by setting them outside during the day for about a week before planting them in the garden.
Plant Seeds Indoors
Get an early start on growing tomatoes by planting seeds indoors about six weeks before the average date of the last frost in your area. This gives the plants time to become established in the warmer temperatures inside while it is still too cold outside for them to grow. Look up the last frost date by finding your area or or hardiness zone on a national frost calendar. Contact your state university extension for a more specific date for your city. If you prefer, buy seedlings from a garden center when it is time to plant outdoors.
Outdoor Planting Date
Plant tomatoes outdoors within about one week of the last frost date. If the weather forecast predicts frost within the next week, delay planting until after that late frost has passed. If you get an unexpected late frost after planting tomatoes, cover them with floating row covers or plastic containers overnight to help protect the plants.
Outdoor Planting Conditions
Wait until soil temperatures outdoors are at least 50 degrees so the tomato plants will grow. For best results, wait until the soil temperature has warmed to at least 60 degrees. If you want to artificially increase your soil temperature, spread black plastic over the garden area where you plan to plant the tomatoes. This plastic absorbs more heat from the sun and warms the soil underneath. Remove the plastic prior to planting the tomatoes.
Latest Planting Date
Plant tomato crops early enough to ensure the fruit ripens on the vine before the first fall frost in your area. To find your last safe planting date, start by looking up the days to maturity for the variety of tomatoes you are planting. This can be anywhere from 45 to 80 days from the transplant date, depending on the variety. Count backwards that many days from the average first fall frost date in your area. Count backwards another 14 days to give you a two-week buffer in case the plants do not mature as quickly as you expect. This date is the latest planting date at which you can safely expect the plants to produce tomatoes before the first fall frost. In regions with warm climates, the latest planting date will occur in late summer for a crop that matures in the fall.