Determining Soil Temperature

Determining Soil Temperature

Many of my seed packets indicate that seeds for certain plants (e.g., beets) should not go in until the ground temperature is at least 40 degrees.

I doubt we’re at 40 degrees yet (not at night, at least), so how do I determine soil temp in my backyard garden.

I looked online but haven’t found any sources of this info yet, though I did find this map which, unfortunately, does not include Chicago – though I see that it’s around 41 in St. Charles, so I’m guessing we have a little time to go before I can plant beets in my backyard.

I think soil temp can vary drastically even within the same garden. I've used a probe thermometer to check the soil temp in different parts of my yard and the areas that get a lot of sun can be 10 or 15 degrees warmer than areas that are mostly in shade. I have a raised section in my yard as well that is warmer than the lower portion by 5 degrees.

At this point I wouldn't worry about putting beets, peas, or radishes in the ground. At worse they'll just take a little longer to germinate.

Attrill wrote:I think soil temp can vary drastically even within the same garden. I've used a probe thermometer to check the soil temp in different parts of my yard and the areas that get a lot of sun can be 10 or 15 degrees warmer than areas that are mostly in shade. I have a raised section in my yard as well that is warmer than the lower portion by 5 degrees.

At this point I wouldn't worry about putting beets, peas, or radishes in the ground. At worse they'll just take a little longer to germinate.

Guess I need a probe.

I have radishes in already, ditto carrots and some microgreens; I'm laying in some leeks this afternoon.

Peas? Hmmmn, wasn't planning on planting any of those, but maybe I should.

Definitely grow peas! I grow a couple rows of sugar snap peas for the pea pods and 4 or 5 rows for pea shoots. It only takes 3 weeks or so until shoots are ready to harvest, so you can grow them in the same place you'll be planting warm weather plants later (peppers, cukes, squash, etc.).

Peas also affix nitrogen to the soil, naturally fertilizing it.

Attrill wrote:Definitely grow peas! I grow a couple rows of sugar snap peas for the pea pods and 4 or 5 rows for pea shoots. It only takes 3 weeks or so until shoots are ready to harvest, so you can grow them in the same place you'll be planting warm weather plants later (peppers, cukes, squash, etc.).

Peas also affix nitrogen to the soil, naturally fertilizing it.

Okay, I'm inspired, though I know very little about growing peas. Must study then plant.

Peas better get in the ground ASAP because they absolutely hate hot weather. Peas have great cold tolerance and are best planted in late March providing the soil is not too wet. Later planting reduces bearing time and hence yields. Peas will be trashed by heat and powdery mildew about the same time in July regardless of when they were planted. Oregon Sugar Pod II is a snow pea that is a bit more heat tolerant than many and might be a good variety to start with. The same also applies to spinach, which bolts in hot weather with long days.

Use a thermometer such as a lab thermometer stuck in the ground for soil temperature readings. Note that the temperature may vary a lot between the top two inches and five inches down in the same spot. In an urban environment with wide variations in shading from buildings there will be substantive differences within a few feet. Moisture content affects soil warming as does spring versus fall tillage. Fall spading or other tillage lets the soil warm up faster in the spring as well as have better condition. With fall spading I use a four-tined cultivator to prepare the soil for spring planting without bringing up colder soil from below.

MMMMMMMM fresh English peas. Not much better in my book. But, as ekrieder noted, they do need to get planted ASAP if you're going to get any yield.

Per the temp, I just took my trusty kitchen thermometer out there and stuck it in. I am only in EBs and SIPs. Today's temp in the box that is affixed to my fence was 60. It's in the sun all the time and I'd thoroughly worked the soil a few days ago, aerating it.

Compare that to the EB that is on the ground - it was 51.