Soil Temperatures for Germination

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Optimal germination and growing temperatures may not come until late spring or early summer. In regions where the growing season is short, waiting for optimal soil temperatures may not be practical or realistic. A 70 percent germination rate is often considered both practical and realistic.

Minimum Soil Temperatures for Seed Sowing and Germination:

• 35°F: lettuce, onion, parsnip, spinach.
• 40°F: beet, broccoli, Brussels sprouts, cabbage, carrot, cauliflower, collards, Asian greens, Chinese cabbage, fava beans, kale, kohlrabi, mustard, arugula, radish, Swiss chard, turnip, pea, radish, rutabaga.
• 50°F: asparagus, celery, celeriac, corn, tomato.
• 60°F: bean, cucumber, eggplant, muskmelon, pepper, pumpkin, squash, watermelon.

 Soil Temperature Needed for 70% Germination:

• 45°F: beets, lettuce, parsley, spinach.
• 50°F: broccoli, Brussels sprouts, cabbage, carrot, cauliflower, collards, Asian greens, Chinese cabbage, fava beans, kale, kohlrabi, mustard, arugula, radish, Swiss chard, turnip, pea, radish, rutabaga.
• 55°F: cabbage, corn, Swiss chard, tomatoes.
• 65°F: cucumbers, peppers.
• 70°F: beans, cantaloupe, melons, squash.
• 75°F: eggplant, okra, pumpkins.

Optimal Soil Temperature for Germination (near 100% germination):

• 65°F: parsnip.
• 70°F: spinach.
• 75°F: asparagus, lettuce, onion, parsley.
• 80°F: bean, carrot.
• 85°F: beet, cabbage, eggplant, pepper, radish, Swiss chard, tomato, turnip.
• 90°F: muskmelon.
• 95°F: corn, cucumber, pumpkin, squash, watermelon.

https://harvesttotable.com/vegetable-planting-and-soil-temperature/
https://www.gardeners.com/how-to/when-is-it-warm-enough-to-plant/9029.html
https://extension.oregonstate.edu/sites/default/files/documents/12281/soiltemps.pdf
http://sacmg.ucanr.edu/files/164220.pdf