Reference
Soil Temperature for Germination, by Crop
The short answer
Germination is driven by soil temperature. Each crop has a minimum below which seeds barely sprout, an optimum range where they come up fastest and strongest, and a maximum above which germination drops off. The table below is drawn entirely from Alabama Cooperative Extension so the numbers are internally consistent rather than averaged across sources.
The practical split is cool-season versus warm-season. Lettuce, spinach, onion, and parsnip will germinate in cold soil (minimums around 35°F), which is why they can be sown early. Beans, cucumbers, peppers, squash, and melons have minimums around 60°F and simply rot or stall if sown into cold ground, so waiting for warm soil beats an early calendar date.
To use it, measure your soil, do not guess. Push a soil thermometer to seeding depth, read it in the morning for several consecutive days, and compare the average to the crop's optimum range before sowing.
Soil temperature for germination by crop (Alabama Extension)
All values are soil temperature in degrees Fahrenheit, listed as minimum / optimum range / maximum, from Alabama Cooperative Extension. Aim for the optimum range for the fastest, most uniform germination; the minimum is where germination is possible but slow, and above the maximum it falls off sharply.
- Lettuce: min 35, optimum 40-80, max 85
- Onion: min 35, optimum 50-95, max 95
- Parsnip: min 35, optimum 50-70, max 85
- Spinach: min 35, optimum 45-75, max 85
- Beet: min 40, optimum 50-85, max 85
- Cabbage: min 40, optimum 45-95, max 100
- Carrot: min 40, optimum 45-85, max 95
- Cauliflower: min 40, optimum 45-85, max 100
- Celery: min 40, optimum 60-70, max 85
- Swiss chard: min 40, optimum 50-85, max 95
- Parsley: min 40, optimum 50-95, max 95
- Pea (English): min 40, optimum 40-75, max 85
- Radish: min 40, optimum 45-90, max 95
- Turnip: min 40, optimum 60-105, max 105
- Asparagus: min 50, optimum 60-85, max 95
- Corn: min 50, optimum 60-95, max 105
- Tomato: min 50, optimum 70-95, max 95
- Bean (lima): min 60, optimum 60-85, max 85
- Bean (snap): min 60, optimum 65-85, max 95
- Cucumber: min 60, optimum 60-95, max 105
- Eggplant: min 60, optimum 75-90, max 95
- Muskmelon (cantaloupe): min 60, optimum 75-95, max 100
- Okra: min 60, optimum 70-95, max 105
- Pepper: min 60, optimum 65-95, max 95
- Pumpkin: min 60, optimum 70-90, max 100
- Squash: min 60, optimum 70-95, max 100
- Watermelon: min 60, optimum 70-95, max 105
How to measure soil temperature
Use an inexpensive soil (dial) thermometer, not a guess or an air-temperature reading. Insert the probe to roughly the depth you plan to sow the seed, small seeds shallow, larger seeds deeper, and let it settle before reading.
Take the reading at the same time each morning for several days in a row, since soil warms during the day and cools overnight; the early reading is a fair daily low and a conservative check. When the multi-day average sits within a crop's optimum range in the table above, it is time to sow. This is far more reliable than a frost-date calendar alone, especially in a cool or late spring.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Alabama Cooperative Extension System - Soil Temperature Conditions for Vegetable Seed Germination — Provides a by-crop table of minimum, optimum range, and maximum soil temperature (F) for vegetable seed germination (e.g., lettuce min 35/optimum 40-80/max 85; tomato min 50/70-95/95; cucumber min 60/60-95/105; watermelon min 60/70-95/105); soil temperature can be measured with thermometers.