The best time to plant tomatoes outside is after the danger of frost has passed and when both the air and soil temperatures have warmed sufficiently. Specifically, wait until nighttime temperatures stay consistently above 50°F (10°C), ideally reach 55°F (13°C), and soil temperature has warmed to at least 60°F (16°C), ideally 65 to 70°F (18 to 21°C). Daytime temperatures should be consistently between 65 to 70°F (18 to 21°C). The last average frost date for your area is a key timing indicator, with planting typically done in late spring. For example, in many temperate regions, this corresponds to mid to late May. Tomato seedlings should be hardened off before transplanting, and it is best to plant them in the late afternoon to early evening to reduce transplant shock. In warm climates with long growing seasons, planting can be done about two weeks after the average last frost date. In colder climates, waiting longer to avoid frost and cold damage is safer, and selecting tomato varieties with shorter maturity times helps ensure a harvest before fall frost. Temperatures below 50°F can harm tomato plants, so planting too early in cold soil or cold nights can stunt growth or kill the plants.
Summary of key planting conditions for tomatoes outdoors:
- After the last frost date in your area
- Nighttime temperatures consistently above 50°F (10°C)
- Daytime temperatures between 65 to 70°F (18 to 21°C)
- Soil temperature at least 60°F (16°C), ideally 65 to 70°F (18 to 21°C)
- Harden off seedlings before transplanting
- Plant in late afternoon or early evening to reduce shock
This timing provides the best chance of healthy growth and a good harvest.
