The soil temperature sensor is now in the ground and measurements have been coming in for days now. I have placed the NSLU2 computer in the windowsill and laid an Ethernet cable out to the raised beds. The scripts for this logging functionality are available here:
owfs is used as interface to the 1-wire network.
As expected the soil temperature is changing slower than the air temperature. Sometimes the soil temperature continues to go up while the air temperature is dropping. Maybe the soil temperature is determined by the amount of sun reaching the ground and the air temperature follows the wind, but I don’t know.
I actually thought that the soil temperature would be more stable, like 7 deg. C +/- 2 (45 deg. F) or something, but that is not the case here. Until now it has been in the range 3 to 7 deg. C (37 to 45 deg. F) and it seems like it would easily go below 0 deg. C (32 deg. F) given enough hours with air temperature below -5 deg. C (23 deg. F). On a second thought it might be true that a few meters down the soil temperature would be rather stable. But then it’s not soil anymore, right?
Anyway, it’s time to plant some garlic. We have some Chinese ones in the kitchen. They’ve traveled about 7000 km (4300 miles) … Geez, what were we thinking?