Warming Your Soil for Spring Planting

Best Way to Warm Garden Soil

Mar 9, 2018
Garden Soil

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Two weeks ago, I had 10 inches of snow in my yard, with more snow predicted. Last year, the daffodils were blooming. So, I set up to experiment with the best way to warm the soil for spring planting! 

We run a plant business and our season is short so it’s important to plant seeds as early as possible. I hope my advice helps you with spring planting, too.

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I put down squares of 1. black plastic, 2. clear plastic, 3. wood ashes, and 4. coffee grounds and tested each for how quickly they melted the snow and how fast they warmed the soil.

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On the few sunny and unseasonably warm days we had Mother Nature did a better job of making the snow disappear than the plastic which seemed to protect the snow from melting. I ended up with 2 snow squares that still haven’t melted!

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The ashes quickly melted right through the snow. The coffee grounds seemed to insulate the snow from the sun’s rays.

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After the snow was gone, I moved the 2 squares of plastic to one of the frozen raised beds to gauge their warming effect.

  • This time, the clear plastic worked best thawing the ground to 6 inches and heating the soil from 36 up to 56 degrees in 4 days! 
  • The black plastic only got to 50 degrees but still thawed the ground down 6 inches.
  • The ashes only thawed down 2-1/2 inches in that time and warmed to 48 degrees.
  • The coffee grounds were 1 inch and 40 degrees.
  • My control patch, which had no help with warming other than the sun, was thawed 1-1/2 inch and warmed to 44 degrees—better than the coffee grounds did!

Lesson learned: Use ashes to melt the snow and then put down clear plastic to heat things up. The clear plastic lets in the sunlight and UV rays and holds in the heat allowing the soil to warm up and the ashes will sweeten the soil and add potassium. If you live in an area that has naturally high pH soil, you’ll have to forego the ashes and wait for Mother Nature to do the melting for you.

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In the vegetable garden we always plan ahead in the fall and put up the pea fence where we will be planting the peas in the spring. This seems to act like a snow fence and prevents the snow from drifting deeply over that bed so it thaws out and warms up first. Good thing since I am very eager to get those seeds in the ground.

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The soil is still pretty cold, it was 45 degrees on the last sunny day but dropped back to 40 today since it is cloudy and raw out. Looking back thru my records, March 11 was the earliest I have planted peas in this garden and I had to replant them on April 2 because of poor germination. Probably rushed the season and the seeds rotted. Even though many seed packets say to plant peas as soon as the ground can be worked, the soil temperature really matters. At 50 degrees, it takes 2 weeks for the pea seedlings to emerge, at 60 degrees only 9 days, and 6 days at 77 degrees.

One old time trick is to plant peas when the forsythia start to blossom. See more clues of planting by nature’s signs.

Now see our video demonstrating how to warm your soil for spring planting.

About This Blog

Get inspired by Robin Sweetser's backyard gardening tips. Robin has been a contributor to The Old Farmer's Almanac and the All-Seasons Garden Guide for many years. She and her partner Tom have a small greenhouse business and also sell plants, cut flowers, and vegetables at their local Farmer's Market.

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warming garden soil early...

try a mixture of ash and green cow manure ....cover with clear poly the fermentation/composting will generate heat. also great for ruhbarb in early spring place green manure and ash in a circle minimum 6 inches from the new tips...helps with late frost to..

Warming soil

I use an amount of turkey "compost". This I purchase from the processing factory (chicken will have same effect). Spread over soil and dig in. In about one day you will see steam rising. It is very easy to get things too hot, and kill seedlings. Some experience will help to get amounts in balance for your climate. Happy planting. T

Thanks for the blog

I have been enjoying your reflections over the past few months and just wanted to throw out a sincere "Thank You" for your thoughts, comments, and on-going, common-sense, hands-on, practical ideas for the rest of us. Thank you. Think Spring . . . (and happy thoughts).

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