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What is the Ideal Soil Temperature for Sowing Vegetable Seeds?

Sowing vegetable seeds in the garden soil

You have spent the latter part of the winter looking through seed catalogs and surfing online garden sites. You’ve ordered your vegetable seeds and grumble when it’s snowing again or when the nighttime temperatures are still causing your furnace to kick on way too often. If you’re anything like us, you can’t wait for the day you can get your hands dirty in the garden.

We know the feeling and we also know how hard it can be to be patient. For many gardeners, the time to plant seeds into the garden is still a ways away, while some warm-climate residents are already happily crawling around on their hands and knees as they sow the seeds for this year’s garden. (We’re jealous!) We thought we would pass along the optimal soil temperatures for sowing vegetable seeds outdoors.

However, there are some vegetable seeds that are best sown indoors and are rarely started right in the garden. For various reasons these seeds will germinate best and produce premium crops when sown indoors and then hardened-off and transplanted outdoors:

  • Broccoli: is best germinated indoors at temps of about 85°F, 6 weeks before you plan to transplant

  • Celery: is best germinated indoors at 75-85°F. These tiny seeds are very hard to sow without overplanting and will have to be carefully thinned to the strongest plants.  A handheld seeder is really handy for these dust-speck-sized seeds.

  • Kohlrabi: is best sown indoors for a spring crop, but can be sown outdoors for a fall crop with soil temps of at least 70°F.

  • Peppers (hot & sweet): are best started indoors at 80°F about 8 weeks before transplant

  • Tomatoes: are best started indoors at soil temps of 70 to 90°F, and then transplanted outdoors when soil temperatures are consistently above 50°F.

Chard is an exception to almost every rule: its seeds enjoy and germinate best in cooler temperatures. As soon as you can work the soil, sow your chard seeds.

The following seeds can be sown directly into the garden when soil temperatures reach a minimum of 40°F:

  • Beets

  • CabbageSowing vegetable seeds with a garden seeder

  • Endive

  • Herbs

  • Parsley

  • Potatoes

  • Turnips

  • Radish

  • Spinach

You can sow the following seeds when soil temperatures reach a minimum of 45°F:

  • Leek

  • Mustard

  • Peas

These vegetable seeds prefer slightly warmer soil and can be sown when soil temperatures are a minimum of 50°F:

  • Carrots

  • Cauliflower

  • Lettuce

  • Onionssmall hand seeder sowing vegetable seeds

  • Corn

These veggie seeds will germinate best when soil temperatures are at least 60°F:

  • Beans

  • Cantaloupe

  • Cucumber

  • Gourd

  • Kale

  • Pumpkins

  • Squash

It may seem late in the season, but these seeds prefer it warm and should be sown with soil temperatures at a minimum of 65°F:

  • Chicory

  • Okra

  • Popcorn

And last, but definitely not least, these seeds really like it warm! Sow them when soil temperatures reach a minimum of 70°F:

  • EggplantThermometer for testing soil temperature

  • Watermelon

  • Kohlrabi (fall crop)

Keep in mind your soil will not necessarily be the same temperature as is shown on your outdoor thermometer. Soil holds and releases heat at varying levels depending upon a number of factors. Your soil may not even be the same temperature as your neighbor’s—especially if you use compost and your neighbor doesn’t. You may use mulch, or over time you may have built your soil to a healthy, fertile level. It IS true that dark soil will hold both heat and water more efficiently; dark soil = healthy soil (in most cases). We recommend you purchase an inexpensive soil thermometer to ensure better germination results on direct-sown vegetable seeds.

One Response to “What is the Ideal Soil Temperature for Sowing Vegetable Seeds?”

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