I’ve been messing around measuring this number recently and seeing what relationship air temperature and soil temperature might have with each other. On the air temperatures, my location is generally 2-4° F cooler than this official reading. The high of 71°recorded on the 23rd was just after midnight and it’s been well below 60°F since, at least for 48 hours. We never reached 50° here on the 24th, the official reading is on the other side of town and it was a lot warmer to the east on the 24th, one of the odd features of this particular air mass. Here, it has been 100 % overcast and misty or with light rain and below 50° and with stints around 38-39° for 48 hours plus.

In spite of that, the soil temperature seems to have stabilized around 60°. It had gotten close to 70° at ~seed levels 2-3 inches just prior to the weather turning colder and was in the mid 60s at 12”, about as far as I work the soil, but all the beds are around 60° now except at very shallow levels where they are a degree or two cooler.

I want to periodically look at soil temperature throughout the year and see what beds are doing what. Doesn’t seem like the raised beds are all that different than the in the ground one at this stage. Mulching hasn’t made a difference yet really either.

I checked this thermometer against another and it seems accurate.

I want to play around with this to see which bed has a tendency to stay cooler in summer or hold on to warmth better. Maybe there won’t be any differences, but I won’t know until I look into it.

@karstopography I do like your compost thermometer, so much so I went and purchased one on Amazon. Besides checking my compost, it may come in handy for checking the pond temperature during these frigid days. The one linked below has the 16" stem, what length is yours?

https://www.amazon.com/REOTEMP-Backyard ... m=1&sr=8-6

@pondgardner 20”

My compost pile is generating a little thermal energy, not a ton, but several degrees above the soil temperature and way above the current air temperature of 45°. I haven’t done anything in long time to encourage the composting process. It is full to the brim. It is One of these Geobin round types that are roughly 1 meter in diameter and about that in height.

This is NOT a waste of time.

Last year I was trying to figure out when to plant peas, and I learned that in spring you can reckon soil temperature to be about 5 degrees less than air temperature. So when we hit 50F days I reckoned the ground would be 45F and the right temperature for peas.
That same source also said that as you get into summer there is less and less difference between ground and air.

I'm a data geek by profession so it doesn't sound like a waste of time to me. Then again, I tracked historical temperatures for 120 years to prove there isn't a correlation between the garden folktale that "we always get a freeze at easter".

Soil type should be considered, too.

I think some soils insulate better than others. Our clay gets pretty cool, even when it's really hot. (If you want a natural air conditioner, just dig a hole and go inside.) I haven't noticed that with looser soil. I should get one of those to test.

The depth matters, too.

@Shule My soils are pretty heavy. I’ve amended all the beds with decomposed organic matter, but even the raised beds have a significant amount of heavy clay. The native soil on which all the beds rest without any barriers is all heavy clay, red clay is some spots and black in others. My garden seems to be on a boundary of the two. There’s also a thin layer of fine silt. Not every raised bed is exactly the same, though, some are a little fluffier with some peat and reed components and a little sand in the mix, all drain pretty well. The biggest bed isn’t a raised bed so much as amended native soil. All beds remain consistently moist, considering the weather outlined below.

I checked a couple of beds today, mid morning. Air temperatures have remained in the low to mid 40s from the previous soil check yesterday. A heavy overcast sky persists with intermittent mists so no chance for the soil to receive much solar energy beyond that which can penetrate a heavy and constant cloud cover. It’s been quite dark, especially for late February, here even at midday so the clouds must be extra thick. Core temperature of deeper, 6-12” soil layers, are down maybe a degree F from yesterday’s check. I’m a little surprised by the relative lack of movement on the soil temperature and relatively inability of the colder air temperatures to influence abrupt swings in the soil temperatures. Soil temperatures at ordinary garden vegetable root depths don’t seem to respond very quickly or abruptly to the temperature of the air, at least with the lack of sunlight influencing the temperatures.

I’ll hopefully keep playing around with this.

" 'we always get a freeze at easter'."

Easter has a pretty wide spread, earliest March 22--latest April 25.

The Gotch

Soil like any heavy material (stone, brick) absorbs heat slowly and also releases it slowly. So it takes more energy to warm it when it's cold but once it is warm it will cool very slowly.
The soil is like any 'passive solar mass' in engineering.
Soil in my greenhouse has not dropped below freezing this winter. Water in 2 liter containers also didn't freeze. But the air temp has definitely been below zero.

Went out this morning and checked soil temperature. We’ve had three days of mostly sun and warm temperatures, a little warmer than on the forecast graph a few posts up.

Soil temperatures haven’t moved much. Beans sprouted nicely in spite of the soil temperature being around 60°. The gaps are all around two or three bamboo stakes and completely missing any sprouts which makes me think I missed planting any seed there.

Cornelius_Gotchberg wrote: ↑Sat Feb 26, 2022 6:08 pm " 'we always get a freeze at easter'."

Easter has a pretty wide spread, earliest March 22--latest April 25.

The Gotch

Not to mention Eastern Orthodox Easter.

Oh, wait, I did.

My soil is at 58 right now and I hope it stays that way for a while. At 65 the nematodes wake up and they need to sleep longer!

Soil temperature as of the morning of March, 31st, 2022.

We're right at 65 right now. That's the point at which the nematodes start waking up.

@GoDawgs based on today and our previous posts from March 6th, your soil temperature is running roughly 5 degrees behind mine.

GoDawgs wrote: ↑Thu Mar 31, 2022 9:38 am We're right at 65 right now. That's the point at which the nematodes start waking up.

It's also the temperature that the plants start growing best.
A coincidence i think not.

Nematodes might be in tune with the plants, yes, that seems to make sense, lol.

At night, sometimes I dream up nematode cures. Covering the beds with plastic and putting in chunks of Dry Ice or flooding the beds with liquid nitrogen.

Maybe pumping in a lot of propane and igniting it. That might cause issues with the neighbors.

@worth1 , that's a great thought! It makes perfect sense. Stuff in nature is so in tune to those rhythms.

I've come to think that planting my most nematode-prone spring stuff behind the overwintered brassicas helps suppress the little bastiges! There was an article I read that mentioned something from the brassicas acting like a repellant. Of course, the effect only lasts so long but by the time it wears off, I'm beginning to think the succession plants' roots have matured enough that it slows down the damage. Still observing that theory.