How do you measure soil temperature? Predictor of pest emergence?

Do an Internet search for "How do you measure soil temperature?" and up comes a bunch of things to buy. I have an extra instant read thermometer for grilling steaks that I can use. Do I really need another thermometer? If I use what I have, how deep do I plunge the thermometer? Morning, noon or night? If you have one of the special soil thermometers, how long do you leave it in the ground?

If you diligently measure soil temperatures, how much does it vary from year to year? Other factors?

Could one correlate pest pressure with soil temperature? Now that could be a worthy project. Has anyone made any observations on that?

Put your money away and don't buy anything. What I do here in Georgia is consult the Georgia Automated Environmental Monitoring Network page. The nearest station is about 30 miles away, but that's good enough for soil temperature as well as evapotranspiration, precipitation, soil moisture and a bunch of other data. If you Google your state and "soil temperature" in the search box, you will probably get a similar FREE government service that is woefully underutilized.

As underutilized as these services are, they are prime candidates for budget cuts, and the tax-cutting fools in the legislature are ready to take their scissors to the nose of all the farmers in the state. It's been estimated that the entire program's budget is less than the damage it regularly prevents to our blueberry crop.

Thanks, John nice to know ! Big AL

John Elliott wrote:If you Google your state and "soil temperature" in the search box, you will probably get a similar FREE government service that is woefully underutilized.

I tried it. It worked! The water conservancy district to the north about 50 miles as the raven flies. Will have to check the altitudes to figure out which station to use.

LOL, I can also find a citizen effort to monitor the prevailing wind coming off the Nevada Test Site should there be a radiation incident. There's a defunct link for wind around the Army chem demil plant in Tooele, now that they have finished burning of the chemical weapons arsenal maybe no one cares. Utah is a weird place.

Wow! You are right!

I was all set to go out every day with a thermometer so I could get extra early sweet corn, but now I do not have to!

Though, since the soil will be warmer during the day I will anyways just before I plant, to be sure. A book I have on corn says that if the soil temp at 2 inches deep is 60 degrees in the morning, then it is time to plant. The evening cool down should not hurt a thing.

As to the original question, any thermometer that can be stuck into the soil about two inches and registers temperatures in the range of 30 to 80 degrees will work. A mercury thermometer will be more accurate, but instant read digital thermometers are more convenient. The mercury will take several minutes to register accurately, depending on how far the mercury has to travel, so to speak. A non-digital, non-mercury, that is a bi-metal, thermometer will be calibrated to a certain temperature (eg. 350 for an oven thermometer) and its accuracy will decline as temperatures vary from that sweet spot. Even so you can follow warming trends as get in the ballpark.

John's answer was very helpful. I figure for most people the information they can get online will meet their needs. But you can still learn a lot about your local growing conditions with a soil thermometer. My "local stations" are 50 and 80 miles away and 1000 and 2000 feet lower in elevation and I expect they are going to give more approximations only. They aren't reporting soil temps now and I don't know when they'll start up in spring. I know from experience I can put plastic over a bed for two weeks and plant several weeks earlier than I would otherwise. My own thermometer allows me to monitor this process.

I have monitored soil temperatures and air temperatures at plant level pretty extensively in figuring out how best to use low tunnels and hoophouses to extend my high desert growing season. I've used instant read digital thermometers to determine how much mulch cools the soil and how much freeze protection you get from various weights, layers and combinations of row cover directly over plants, on wire hoops just above plants, and on pvc hoops further above the plants. I learned that plastic low tunnels give lots of heat on a sunny day, but basically no heat retention at night. Row cover protects at night, but does a better job if covered with plastic. A layer of the lightest cover directly over the plants is beneficial if there is another layer held above it by hoops. Part of my garden is protected by a south facing cinder block retaining wall. For every 3 or 4 feet away from this wall, the soil temperature in early spring decreases a degree or two until at 15 feet or so there is no warming effect.

Every year, every season is slightly different. I haven't made any correlations with "pest" pressure. Gophers are active year round and seem to appreciate that I warm the soil with low tunnels for them.

Old-timers say plant corn when the oak leaves are in mouse ear stage. Having the experience to make such observations is even better than looking at soil temperatures.

I have an old bi-metal meat probe thermometer that is used strictly for soil purposes. It was like $3. I've tested it against numerous other thermometers, (digital, mecury, and other bi-metal) and it is just as accurate. The display is off by 10 degrees, but it is accurate; assuming I can remember to add the 10 degrees to the reading displayed.

I can stick it in compost, soil, containers, worm bins, etc.... Well worth the $3, IMO.

Just to chime in from another location
http://climate.rutgers.edu/njwxnet/station.php?s=1032

This station is within a few miles of my NJ home, and it lists not only soil temperatures, but various insects and their "degree hours" - I am not at all sure quite what that means, but I am sure there's a way to gain understanding and then be informed.

And I am betting that the fact this weather station has reporting linked to various insects means that someplace, someone has done the studies about which insect pests start getting active at what temperatures.

If anybody cannot find this info for their state, ID has a system which is tied to a national system.
Go to IDaho Farm Bureau
There will be a national map, as well as regional maps. If you click any of these, they enlarge.
See attachments: US, and NW region

(As you can see, most of the inhabited parts of Canada are also included.)