Understanding soil temperatures, rather than just the calendar dates, allows gardeners to get planting earlier by matching seeds to ideal soil temperatures for seed germination. Especially with local unpredictable spring air temperatures this can make or break a garden season.

Let’s dig into soil temperatures for early season success.

Radishes germinate with low soil temperatures

Climate Change in the Garden

Cool weather crops germinating early in the spring garden raised beds

While specific years will always fluctuate, the country and Northern world is experiencing a long-term trend of warming winters. Minnesota’s average annual temperatures have increased by 3.2°F between 1895 and 2024.

Spring soil temperatures in Minnesota show significant year-over-year variability, heavily influenced by snow cover, spring precipitation, and air temperature, with a long-term trend toward earlier warming. Minnesota is recording earlier spring soil warming temperatures overall.

In recent years, soil temperatures have varied from early-season warm spells to late-season “nosedives,” with 4-inch deep soil temperatures commonly reaching 50°F in April. But we still get anomalies like April readings of 33°F in 2014 and 60°F in 2012.

How to Measure Soil Temperature for Seed Germination

Knowing soil temperature for seed germination is key

This spring in my Minnesota garden in mid-May I still had soil temps dip down below 50°F in the early morning, and we’re still having frosts this May. In recent years this temperature was higher.

Planting in protected growing areas like Low Tunnels or a Cattle Panel Greenhouse can increase soil temperatures by 10–15°F compared to open ground, promoting faster, healthier growth. These consistent few degrees warmer means so much for good germination early in the season.

  • Use a simple soil thermometer
    (I actually have a few of them) and test roughly 4-6 inches deep to get my readings.
  • To know the low temperature you have to check it before the sun starts warming it for the day.
  • Leave the thermometer in the soil for at least 5 minutes before reading so it can level off

Each seed has its own ‘happy place’ temperature range. And trying to push the season by planting out a seed before the soil is warm enough means that seed will likely rot in place. So be patient for your soil to warm up, or help them along with covering.

Seed Germination Temperature Chart

Spinach growing in ground in a garden

Minimum Soil Temperatures for Germination

  • Beans – 60°F
  • Beets – 40°F
  • Broccoli + Cauliflower – 45°F
  • Cabbages – 55°F
  • Carrots – 45°F
  • Corn – 55°F
  • Cucumbers – 65°F
  • Lettuce (most greens) – 40°F
  • Melons – 70°F
  • Onions – 40°F
  • Peas – 40°F
  • Peppers – 65°F
  • Tomatoes – 60°F
  • Spinach – 35°F
  • Squash/Zucchini – 70°F

Direct Sowing Versus Starting Indoors

This above graph information combined with which plants to direct sow versus which to start indoors can help you get your garden rolling as early as possible- giving many more harvests throughout the seasons.

It also means I can stagger my planting times, so beans will be going into the soil in about a week, while radishes and spinach were direct sown weeks ago.

Depth matters – deeper soils hold warming easier, shallow (over rock) cool quicker. The amount of sand and how damp the soil is overall also has a real impact. In general soil still warms and cools the most in the first inch.

Knowing both air and soil temperature for seed germination help with gardening success

While damp soil holds more heat than dry soil, evaporation of that excess moisture consumes heat which is a cooling process. Avoid bone dry soils AND oversaturated soil for optimal warming of non-covered soils in spring.

It also matters how deep you’re planting that seed. Smaller seeds like lettuce and carrots usually are planted closer to the surface, which is warmer than 6” down. But can also cool off more. But this cooling is easily moderated by adding a layer of fleece or plastic row cover to the seeds.

For more information on Starting Seeds Read THIS ARTICLE

Soil Temperature FAQ:

What temperature do seeds germinate at?

Seeds vary widely in their preferred germination temperature range. From soil temperatures starting at just above freezing at 35°F to 75°F depending on where the seed naturally developed. So when northern gardeners want to grow warm weather crops, we need to trick seeds into germinating by raising temps inside.

Can I use a Meat Thermometer to Measure Soil Temperature?

While you can use a meat thermometer to measure temperatures, it is best to use a tool meant for outside if you plan on keeping it outside. The soil thermometers also have a different range of temperatures and larger font.

Air temperature matters, but soil temperature for seed germination matters more

Does soil temperature matter more than air temperature?

Short answer is Yes, but really, it depends… In general, seeds know what the soil temperature should be to germinate, remember they only have one shot. They are not reading the air temperature because they are in the soil.

But (there’s always a but), if you’re raising the soil temperatures by growing undercover you need to be more aware of late spring cold snaps that can kill off above ground plant greens. But if you start with the cool weather crops, you should be safe.

Air temperatures do matter, and most states gather this data and make it available online. In Minnesota our DNR hosts an interactive map with frost and freeze date probabilities that I find invaluable.

All of this is to say…

Know what your soil temperature is.
Know what temperature your specific seed prefers.

You’ll have better germination, less plant stress and a happier overall gardening experience…

So, when the time is right–
Dig In,
Michelle