@karstopography Thank you! Ive never been much for using black fabric to help to warm the soil, but I think I have some to experiment with. I will pass on my findings if you are interested.

We're having such a cold spring, I just ordered a soil thermometer as well. Definitely worth paying attention, and I'll be interested to hear your results with the fabric too, @CtGrower .

@bower @karstopography

Well the initial results are in, and so far clear plastic has warmed the soil the most in 1 day. We had a beautiful warm partly sunny day today so I'm sure that had an impact. The low this morning was 49F and high today was 70F. It is projected to be 50F tonight.

What I did was put down some garbage bags that I had. The black is 3mil thick single layer and the clear is 1.1 mil thick in a double layer. I put them down last night and measured the soil temps at 4" and 6" depth and then averaged those temps. I measured areas with no plastic, black plastic and clear plastic that were in proximity of each other to have the same conditions.

I measured the temps before putting plastic down on 5/25 and again at 9AM and 4PM today, 5/26. The results are plotted below.
The soil was warmer with either plastic (+2deg in morning and +4deg(black), +6deg(clear) in the afternoon). I will continue the study for at least another day. I'm curious to see how well the temperature is retained overnight.

Another interesting observation from this afternoon's measurements. It's not a surprise that the temperature at 4" was significantly warmer than at 6". The measurements at 4"/6" were: no plastic 63/59, black plastic 68/62, clear plastic 72/63. (edited to correct black data)

I'm feeling more optimistic to plant soon.

If you are in the US, ask your local Extension office , or do a search for the State Climatologist to see if they have a link for statewide soil temperature charts. In Nebraska the Ag Dept publishes a soil temperature chart via CropWatch at 4 inches. Pretty spot on with a weather station set up by a local retired meterologist. Now I use my soil thermometer (which I used to carry in my purse) infrequently and only when I sample my raised beds.

https://cropwatch.unl.edu/soil-temperature/
https://nemesonet.unl.edu/

- Lisa

Local conditions are so variable. You can't beat your own on site data, IMO.
It's surprising how much you can modify air temperature with a little cover. I know my starts of greens and strawberry plants here have survived quite a few frosty nights in recent weeks. Very interested in how you can modify soil temperature, it's definitely worth looking into for these dicey spring conditions!
Thanks for sharing your data @CtGrower !

greenthumbomaha wrote: ↑Mon May 26, 2025 5:28 pm If you are in the US, ask your local Extension office , or do a search for the State Climatologist to see if they have a link for statewide soil temperature charts. In Nebraska the Ag Dept publishes a soil temperature chart via CropWatch at 4 inches. Pretty spot on with a weather station set up by a local retired meterologist. Now I use my soil thermometer (which I used to carry in my purse) infrequently and only when I sample my raised beds.

https://cropwatch.unl.edu/soil-temperature/
https://nemesonet.unl.edu/

- Lisa

Interesting, I have not seen a soil temp map for Ct or Northeast. If there is one, it may not be perfect, but it could be useful to calibrate local conditions to the data station data. Thanks for sharing.

One last update on the plastic soil warming study. I measured for another day. I found it interesting that even though the clear plastic was warmer than black plastic in the afternoon, the soil temperatures were about the same in the morning. Maybe because the clear plastic was 30% thinner? Clear still has slight advantage. Use of either plastic raised soil temps over bare soil.

The 2 days I had the plastic on were very warm sunny days. I wonder how much benefit plastic would have on cloudy days? But that will remain a question for now because...I planted yesterday!!

Soil temps are very important or several crops, light colored bean seeds and corn in particular. Good ino in this thread, thanks to all for the info.