Garden Reviews Seed Vegetables

Soil Thermometer – Knowing the Best Time to Plant

I’m sure you’ve noticed that about every seed pack and every “how to plant” article for spring crops starts out advising us to sow when the ground is workable.  So, we do.

How many times have you planted radishes, lettuce, peas, and other crops and waited 10 days, 2 weeks, or more for them to germinate.  In other years they’ve come up within a day or so.

As I have mentioned so often, each year has many variables.  Planting when the “soil is workable” does not consider the variables.  But if you time your planting based on soil temperature, you have a better chance of getting your crops off to a good start.

Optimal Soil Temperature Charts

There are plenty of charts on the internet that help you out by showing the optimal soil temperature for germination of various crops. One of my favorites is  But when planting without a soil thermometer you’re just guessing at best.

I ordered mine today.

A Significant Benefit for Warm Weather Crops

It will be especially helpful in determining when to set tomatoes and peppers in the garden.  If the soil is too cold they just sit there.  And I recently read that pepper plants can be stunted all season if planted when the soil temperature is under 70 degrees.  I have my suspicions this has happened to me, but with a soil thermometer I can avoid it in the future.

You’ll Know When to Expect Germination in Your Cool Weather Crops

I’m looking forward to knowing the soil temperature when I plant my peas and other cool weather crops.  According to the soil temperature chart the optimum temperature for quick germination of peas is 77 degrees.  Also according to the chart, if I want to plant at 50 degrees I can, but germination will take about 14 days.

Almost a Must to Know What’s Going on with Seed Started Indoors

Last year because of the cool spring my tomatoes didn’t germinate in my flats until June!  I would not have had tomatoes by July 4th had it not been for a good friend sharing some of his starts with me.  This year I have determined to try at least one flat of tomatoes inside. My soil thermometer will indicate if the soil temperature is right.

It’s Pretty Simple to Use.

  • You want to find consistent ground temperature over three days.  (Or average the temperature out over 3 to 5 days.)
  • Take the temperature at mid-day.
  • Leave the thermometer in the soil a few minutes before taking the reading.
  • When you are preparing to plant seeds get your measurement for soil temperature from the first 2 or 3 inches of depth.  Most seeds require the temperature to be consistent for this depth.
  • When transplanting measure 5 to 6 inches deep.

A Tip for Keeping Your Soil Thermometer Visible

I know one thing I’m going to do immediate upon receiving mine — and that is — paint the top red so I won’t loose it in the soil.  (I have lost tools for a year or more because when I turned around to look for them I couldn’t find them.)

Final Words

I think this little tool is going to be one of my favorite things. It runs about $6 to $10 (stainless steel is more) and can take the guess work out of when to plant.



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  • The “Planting by the Phases of the Moon” section in How to Grow More Vegetables by John Jeavons is interesting. I’ve found it to be helpful to promote seed germination. There is a straightforward explanation of the process.

  • Hi Terran,

    Your comment was timely — at least for me.

    I’ve been reading quite a bit about biodynamics farming this year, most especially when I wrote the post Organic Food What are our Options.

    I like the entire concept because it works with the earth’s forces for healthier soil and food. It is indeed a beyond-organic approach.

    I am looking forward to reading the material by Mr. Jeavons that you suggested.

    Thanks so much for taking time to comment.

    Best regards,

  • Love your site with all the ideas and helpful information. I am just sad that it often does not relate to my zone 5 dry climate. Your gardens always seem about a month to 3 weeks ahead, except when it comes to frost dates.

    Thanks so much for sharing and I will keep checking in…

  • Hi Bonnie,

    So glad you love TMG and find it helpfl.

    I know it can be inconvenient sometimes that I’m about 3 weeks ahead. But at least you receive the information at a better time than if I was 3 weeks behind. 🙂

    Have a great summer!

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