For daily wit & wisdom, sign up for the Almanac newsletter.
Gardening in regions with a short growing season can be an adventure. There always seems to be another spring snowstorm around the corner! To take advantage of every possible growing day, we need to get our snow melted and garden soil thawed as quickly as possible.
We run a plant business here in New Hampshire, where our growing season is short, so it’s important to get seeds in the ground as early as possible. To this end, I tested a few common methods for melting snow and warming the soil. I hope my advice helps you with spring planting, too.
Melting the Snow in the Garden
First, I put down squares of black plastic, clear plastic, wood ashes, and coffee grounds and tested each for how quickly they melted the snow.
Clear and Black Plastic: On the few sunny and unseasonably warm days we had, Mother Nature did a better job of making the snow disappear than either of the plastics, which actually seemed to protect the snow from melting. I ended up with two snow squares that still haven’t melted!
Wood Ashes: Surprisingly enough, the wood ashes quickly melted right through the snow.
Coffee Grounds: The coffee grounds seemed to insulate the snow from the sun’s rays, like the plastic, which resulted in little melting.
Warming the Garden Soil
After the snow was gone, I moved the two 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°F in 4 days!
The black plastic only got to 50°F, but still managed to thaw the ground down 6 inches.
The wood ashes only thawed down 2-1/2 inches in that time and warmed to 48°F.
The coffee grounds were 1 inch and 40°F.
My control patch, which had no help with warming other than the sun, was thawed 1-1/2 inch and warmed to 44°F—better than the coffee grounds!
Best Ways to Melt Snow and Warm Soil
Use wood ashes to melt the snow and then put down clear plastic to warm the soil. The clear plastic lets in the sunlight and UV rays and holds in the heat, allowing the soil to warm up.
One thing to note is that ashes will raise the pH of the soil (and add potassium), so if you live in an area that has soil with a naturally high pH, you’ll want to forego the ashes and wait for Mother Nature to do the melting for you. Learn more about how to test your garden soil.
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!
The soil is still pretty cold, it was 45°F on the last sunny day, but dropped back to 40 today since it is cloudy and raw out. Looking back through 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. It 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°F, it takes 2 weeks for the pea seedlings to emerge, at 60 degrees only 9 days, and at 77 degrees only 6 days.
Learn More
One old-time trick is to plant peas when the forsythia starts to blossom. See more clues of planting by nature’s signs.
Check out this video to see more ways to warm the garden soil.
Robin Sweetser is a longtime gardening writer, editor, and speaker. She and her partner, Tom, have a small greenhouse business, selling plants and cutting flowers and vegetables from their home and lo...
Albedo is a measure of how much light is reflected off a surface. Clean snow reflects most light. Wood ashes absorb the sunlight to melt the snow. A similar effect can be achieved with dry sand or dusty soil (especially with low organic content). Gather it dry in a 5 gallon bucket during warm season, set aside until needed. It will not change the pH like ashes do.
Reply to comment
Lisa WrightTue, 03/19/2019 - 06:46
Silly question, once it warms up, doesn't it get cold again and kill the plants? Is this to get seeds in the ground and you keep it covered?
Reply to comment
SamTue, 03/19/2019 - 09:40
If it's too early in the year, I would think so. I think there was something about that towards the end of the article where in a previous year, the soil was "workable" but still too cold for the peas. I think maybe waiting a day or so without anything on top of the soil and then taking the temperature again would work?
Spring weather is fickle and unreliable. Soil temps vary day to day depending on how cold it has gotten the night before and how much sun the plot has gotten during the day. It does pay to wait until the soil temperature readings are more consistent.
This is for starting those early seeds, things with seed packets that say they can be started "as soon as the soil can be worked". If the soil does not stay consistently warm enough, it may delay germination or even cause the seeds to rot. It is a gamble that could reward you with an early crop ...or not. Be sure to have extra seeds on hand just in case a second planting is needed later on.
Reply to comment
JenTue, 03/12/2019 - 18:45
We used to put wood ashes on the icy patches in our driveway for traction, guess I know why now. Thanks for your experiment!! I can so understand trying to rush spring!
Reply to comment
William StiresSun, 03/10/2019 - 11:44
I have taken to starting my peas indoors. I can start 50 plants in a regular flat. they germinate better and once they are 4" high, can be planted outdoors. these plants can withstand a mild frost, but I usually place a light cover over them until they get established.
It is an oldie but goodie I inherited from someone years ago. It has no markings or brand name on it but it works great and I haven't broken it yet!
Reply to comment
JohnyWed, 03/14/2018 - 02:49
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..
Reply to comment
Trevor MextedTue, 03/27/2018 - 07:22
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
Reply to comment
Kathy DiMon, 03/12/2018 - 17:06
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).
Albedo is a measure of how much light is reflected off a surface. Clean snow reflects most light. Wood ashes absorb the sunlight to melt the snow. A similar effect can be achieved with dry sand or dusty soil (especially with low organic content). Gather it dry in a 5 gallon bucket during warm season, set aside until needed. It will not change the pH like ashes do.