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Vegetable Planting and Soil Temperature

The ideal or optimal soil temperature for planting and growing most vegetables is 65° to 75°F.
Soil temperature planting
The ideal or optimal soil temperature for planting and growing most vegetables is 65° to 75°F.

Vegetable seeds and seedlings require minimum soil temperatures to germinate and grow. Seeds and seedlings require optimal soil temperatures to thrive.

Soil temperature triggers not only seed germination but is an important factor in soil chemistry. Soil chemistry includes the release (dissolution) of mineral nutrients in soil moisture. Mineral nutrients are essential for vegetable plant growth and maturation to harvest.

The ideal or optimal soil temperature for planting and growing most vegetables is 65° to 75°F (18°-24°C).

Taking Soil Temperature

Soil temperature can be measured with a soil thermometer or gauge. Most home vegetable gardeners use a soil thermometer—a thermometer attached to a metal probe several inches long which is inserted into the soil.

The soil temperature for seed sowing should be taken between 1 and 3 inches deep. The soil temperature for transplants should be taken at 4 to 6 inches deep.

Commonly the temperature reading is taken after the thermometer has been in the soil for a couple of minutes.

Soil temperature is best taken in the early morning when the soil is coolest and not yet warmed under the day’s sun.

Take the soil temperature for at least three consecutive days and then average the results. Don’t depend on just one reading.

Planting and Soil Temperature

Vegetable seeds can be sown in the garden early in spring before the soil has warmed to optimal germination temperatures. If you sow early before temperatures are ideal, you cannot expect optimal germination.

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.

You can use the minimum soil temperature for germination and the optima soil temperature for germination to decide at about what soil temperature you want to get started sowing seeds and setting out transplants.

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.

For specific soil temperature requirements for crops you are planting see the How to Grow articles for each vegetable and herb. There are more than 60 crops covered in the How to Grow category.

Workable Soil Test for Direct Seed Sowing and Transplants:

Before soil thermometers were used in gardens and farms, the common method of determining when to plant was soil workability. (This is the tried-and-true old fashioned way to know when to plant.)

The soil is workable and ready for seed sowing or planting if it passes the Workable Soil Test. Here’s the test: squeeze a handful of soil in the palm of your hand; when you open your hand if the soil remains a wet or very moist clump, it is not workable. Let the soil dry. If the soil crumbles from your hand with a touch, it is workable.

When the soil is workable in spring, you can:

  • Direct sow: collards, kale, lettuce, parsnip, peas, radish, rutabaga, spinach, turnips.
  • Transplant out: broccoli, Brussels sprouts, cabbage, onion.

Of course, once the soil is workable in spring, it will continue to warm. Often, old-time farmers would look to lilacs and other spring flowering plants to decide when to plant. For more on this is see the articles on Phenology: Nature Planting Signals for Vegetables.

More tips at: Pre-Warm Your Soil Before Planting Vegetables

See also: Soil: Making the Kitchen Garden

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8 Comments

  1. Hello,
    I have been scouring the internet and books to find a chart of EACH vegetable plants specific NPK needs from seed to harvest. All info is non specific and nothing speaks to specific on any of the stages. This info in an easily accessible format would be a godsend, especially for a new gardener that is lost like myself! Any guidance would be helpful. Thanks!
    Becky

    • There are many variables that come into play when growing vegetables: soil composition and texture; soil pH and nutrient composition; weather air, and soil temperature; garden orientation, sun exposure, day length, and length of growing season; rainfall and irrigation–these are a few. These factors and others affect nutrient uptake and plant growth. One chart that would speak to ALL of these growth influences from seed to harvest and to EVERY microclimate and garden would be all but impossible to compose. Adding aged compost to your garden regularly will bring your soil pH to near neutral, that will allow for the uptake of most nutrients. Aged compost (or commercial organic planting mix) will also add a wide spectrum of nutrients to the soil; keeping the soil evenly moist will allow for the uptake of the nutrients. To aged compost, you can add an all purpose organic fertilizer. Organic fertilizers break down slowly and feed plants over weeks and months.

  2. I’ve planted cucumber seeds in large containers and the soil temp varies from 100 degrees on a warm sunny day down to 60 or slightly below in early morning. Can the seeds handle a large temperature swing, or does it need to stay consistently in the listed range? I give it some afternoon shade so it doesn’t go above 100, Should I also cover the pots at night to keep them a bit warmer? Thanks.

    • Temperatures in the 60sF are on the low end of what a cucumber plant will tolerate for growth. On the other hand, 100F is hot–even for cucumbers.
      Place a frame or four posts at the corner of your planting bed then drape shade cloth across the top. This will allow the plants to get morning and afternoon sun but will shelter them from the hot midday sun. The cloth will also protect the plants from chilly night temperatures.

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