Soil Temperature Chart: Best Soil Temps for Planting Every Vegetable

Soil temperature is the number that decides whether a seed will germinate or rot. Air temperature gets the headline forecast, but a planting decision lives or dies on what the soil reads at 4 inches deep on the morning you sow. Below is the full crop-by-crop chart, how to measure soil temperature properly, and how to warm soil up faster when spring is running late.

Why Soil Temperature Matters More Than Air Temperature

A 70-degree afternoon does not mean 70-degree soil. Air heats fast and cools fast. Soil heats slowly because water holds heat better than air, and soil moisture is what most seeds care about. Below the germination threshold, a seed sits in cold wet ground with no metabolic activity, no root push, and a high risk of fungal rot. Above the threshold, the seed sprouts. The threshold is specific to the species.

How to Measure Soil Temperature

Use a soil thermometer (an instant-read kitchen thermometer works) pushed 4 inches deep into the actual planting bed, not next to it. Read in the morning, before the sun has heated the surface. Take readings on three consecutive mornings; the average is your planting number. Soil under black plastic mulch or in a raised bed will read warmer; soil under heavy mulch or in shade will read colder.

Soil Temperature Chart by Crop

Optimal germination ranges from USDA, Cornell, Texas A&M, Oregon State, and University of Minnesota extension data:

Cool-season vegetables.

Lettuce: 40 to 75 degrees, ideal 60 to 70.

Spinach: 40 to 75 degrees, ideal 50 to 70.

Peas: 40 to 75 degrees, ideal 60 to 75.

Kale: 45 to 85 degrees, ideal 60 to 70.

Radishes: 45 to 85 degrees, ideal 65 to 75.

Beets: 50 to 85 degrees, ideal 65 to 75.

Carrots: 45 to 85 degrees, ideal 70 to 80.

Onions: 50 to 85 degrees, ideal 70 to 75.

Garlic (cloves): 50 to 85 degrees. Plant in fall for spring harvest.

Broccoli, cauliflower, cabbage: 45 to 85 degrees, ideal 65 to 75.

Warm-season vegetables.

Beans (snap, pole, bush, lima): 60 to 85 degrees, ideal 70 to 80.

Corn: 60 to 95 degrees, ideal 70 to 85. Below 50 degrees, kernels rot.

Cucumbers: 60 to 95 degrees, ideal 75 to 85.

Squash, zucchini, melons: 70 to 95 degrees, ideal 75 to 85.

Sunflowers: 70 to 85 degrees, ideal 75.

Heat lovers (start indoors, transplant when soil is warm).

Tomatoes: 60 to 85 degrees soil for transplants, ideal 70 to 80. Below 60, growth stalls.

Peppers: 65 to 85 degrees, ideal 75 to 85. Below 60, fruit set fails.

Eggplant: 70 to 85 degrees, ideal 75 to 85.

The 50-Degree Threshold

If you remember one number, remember 50. Below 50 degrees soil temperature, almost no warm-season seed will germinate, but most cool-season crops will sprout fine. The cool-season window opens at about 40 degrees and closes at about 75 degrees. The warm-season window opens at about 60 degrees and stays open through summer. Planting dates that ignore this number explain about half of all garden disappointments.

Air Temperature vs Soil Temperature

Soil temperature lags air temperature by roughly 4 to 6 weeks in spring and runs warmer than air in fall. The lag is what makes early-spring planting risky and late-fall planting deceptive. Last-frost date is a useful guide for the air, but soil temperature is the actual planting trigger.

How to Warm Soil Faster

Black plastic mulch. Lay over a planting bed two to three weeks before planting. Adds 3 to 10 degrees to soil temperature. Especially useful for tomatoes, peppers, melons, and sweet potatoes.

Raised beds. Drain better, warm 1 to 2 weeks earlier than ground beds. Worth the construction time for warm-season crops in cool climates.

Cloches and row covers. Translucent covers trap solar heat. Add 5 to 10 degrees during the day, hold a few of those degrees overnight.

South-facing slope. If you have one, use it for the heat-lovers. South aspect in the Northern Hemisphere captures more direct solar radiation.

Pull mulch back temporarily. Heavy organic mulch insulates cold soil from warming sun. Pull it back two weeks before planting, replace after seedlings emerge.

Best Days for Planting

Once soil temperature is in range, the Farmers’ Almanac Best Days framework adds the lunar timing. Aboveground crops (lettuce, beans, corn, tomatoes) plant on the waxing moon, between new and full. Root crops (carrots, beets, potatoes, onions) plant on the waning moon, between full and new. For specific dates, see our gardening by the moon calendar. For the lunar mechanics behind the rule, see our piece on the crescent moon.

Frequently Asked Questions

What is the ideal soil temperature for planting tomatoes?

70 to 80 degrees Fahrenheit at 4-inch depth. Tomato transplants will tolerate 60 degrees but growth will stall. Below 60, fruit set fails. Wait until soil readings are 70+ for at least three consecutive mornings.

When can I plant lettuce and peas?

Soil temperature of 40 degrees Fahrenheit and rising. Both germinate slowly at the low end and faster as the soil warms toward 60. Both will bolt or stall once soil exceeds 75. Cool-season crops want a window between 40 and 75.

How do I measure soil temperature?

Push a soil thermometer (or instant-read kitchen thermometer) 4 inches into the planting bed. Read in the morning. Take readings three days in a row and use the average. Always measure where you intend to plant, not nearby.

How can I warm soil faster in spring?

Black plastic mulch laid two to three weeks ahead of planting adds 3 to 10 degrees. Raised beds warm 1 to 2 weeks earlier than ground beds. Row covers and cloches add 5 to 10 daytime degrees. Pull heavy organic mulch back temporarily so the sun can reach bare soil.

Why does my soil feel warm but the thermometer reads cold?

The top inch can warm dramatically during a sunny afternoon while the soil 4 inches down is still cold. Seeds and roots care about the deeper number, not the surface. Always measure at planting depth, not at the surface.

What is the minimum soil temperature for corn?

60 degrees Fahrenheit. Below 50 degrees, corn kernels rot in cold wet soil. Wait until soil reads 60+ for three mornings straight. Some short-season varieties tolerate 55 degrees; check the seed packet.