Seed Germination Temperature and Timing

Soil Temperature Conditions for Vegetable Seed Germination

Many internal and environmental conditions influence seed germination: seed condition, water availability, sufficient air, soil conditions, and temperature. The chart below lists the optimum soil temperatures at which they do best. This does not mean your seeds will not germinate at higher or lower temperatures, but greater success will be achieved if optimum conditions are provided. Using a probe-type thermometer is an accurate method for testing soil temperatures prior to planting seeds and small plants.

Source: California Master Gardener Handbook, 2nd edition, Regents of the University of California, Division of Agriculture and Natural Resources, Publication 3382 (Table 5.2, page 114).

*Note: Celery requires diffuse light and a night temperature from 10° to 15°F lower than the day temperature for good germination. Optimal conditions are 85°F day, 70°F night with diffuse light and high moisture.

Number of Days for Vegetable Seeds to Emerge at Different Temperatures

This chart shows the temperature range at which seeds will germinate. Note that temperatures higher or lower than the optimum soil temperature (as noted on the previous chart) will result in more days before germination occurs, or if temperatures are too extreme, germination may not result at all. For example, the optimum temperature range for tomatoes is 65° to 85°F (see previous chart). Within that range, it takes about 6 to 8 days for seeds to germinate. Tomato seeds may still germinate at 50°F, but it will take over 40 days, and there will probably be no germination if the soil temperature is 104°F.

Sources: J. F. Harrington, Department of Vegetable Crops, University of California, Davis, Agricultural Extension Leaflet, 1954

“The New Seed-Starting Handbook”, Nancy Bubel, 1988, Rodale Press

Notes: 0.00 = little or no germination

--- = not tested

August 2017, updated. December 2015, revised and February 2013, written by UCCE Sacramento County Master Gardener Gail Pothour, reviewed by UCCE Master Gardeners Kim Brady, Dan Vierria, and Dave Vaughan. Edited by Judy McClure, UCCE Sacramento County Master Gardener Coordinator.