Soil Temperature for Planting Vegetable Seeds

Tom Fowler
University of Missouri Extension Horticulture Specialist - Buchanan County

One factor for successful seed starting is soil temperature. The measure of a consistent soil temperature is much better indicator of when to plant seed than air temperature or the calendar. If the soil is too cool when seed is planted they can rot if it is too warm the seed can die. There is a research- based optimum range of temperatures for vegetable seed to germinate. By using the soil temperature information from the Missouri Commercial Agriculture Automated Weather Station Network a vegetable seed germination tool has been developed to provide information on the optimum range for seed germination. Research has provided a minimum temperature for seed germination. For example beans will germinate at 60 degrees and above and no warmer than 95 degrees. There is an optimum temperature of 80 degrees for bean seed to germinate. In general we should plant between the minimum 60 degree and 80 degree optimum planting. If we wait until the optimum soil temperature is met it may be later in the season when other factors (heat, drought etc.) come into play that could reduce the development of the plant. For practical purposes we can start planting as soon as that average minimum soil temperature is met. The chart indicates the minimum and maximum germination temperature ranges for each crop. Red indicates the soil temperature is too cool or too hot for seed germination. Yellow tells us we are getting close to the time to plant and green indicates it is time to start planting seed.

Another factor to consider when planting is the calendar dates. If the soil is at optimum temperature it may be too late in the season to grow a successful crop. Also some vegetables are best planted as started plants For information on dates to plant seed and what vegetables are best planted as started plants see the Vegetable Planting Calendar - https://extension.missouri.edu/publications/g6201.

By combining the knowledge of the optimum range of soil temperatures to seed or set out transplants and the time to plant the chance for establising a successful crop increases.

For further information about planting vegetables, contact your local
University of Missouri Extension office to find your Regional Horticulture Specialist.

For more information about the Horizon Point system,
contact us at 573-882-4827 or
HorizonPoint@missouri.edu