Soil Temps & Taters

By Paul James

The other night my son asked me if it was time to plant potatoes. I paused momentarily to soak in the pride I felt knowing that he, along with his younger brother, have made gardening a part of their lives. (I’m sure their sister will do likewise once she moves out of her tiny apartment in Queens, NY.) Then I turned to him and said, “Check the four-inch soil temperature.”

“What’s that going to tell me?” he asked. “It’s going to tell you when you can plant potatoes,” I said.

Savvy veggie gardeners know that deciding when to plant is tricky. On the one hand, an early start means an early harvest, and cool-season vegetable crops do best when grown under cool conditions. On the other hand, getting started too early can lead to crop failure if temperatures nose dive.

However, because potatoes are planted below ground, deciding when to plant is based not on air temperatures but rather on soil temperatures, and when the soil temp hits 40 degrees (technically, when the four-inch bare-soil temp hits 40), you can plant away. The same is true of asparagus, rhubarb, and horseradish because they too are planted below ground, where they’re safely insulated from the cold.

Truth is, you can use soil temperatures to decide when to plant any and all veggies from seed. At 45 degrees, it’s safe to sow cool-season crops such as beets, carrots, lettuce, radishes, and spinach. But for warm-season crops it’s best to wait until soil temps are at or near 70 degrees (think beans, cucumbers, peppers, tomatoes, melons, and such).

And just how do you know what the four-inch soil temperature is? That’s easy. Go online to Oklahoma Mesonet www.mesonet.org or install the app on your phone. The Oklahoma Mesonet is a world-class network of 110 environmental monitoring stations scattered across the state, and it’s run by scientists from OU and OSU. The site displays real-time weather information of all kinds, and detailed maps of soil temperatures.

Of course, there’s always the possibility that air temperatures may plummet once everything is up and growing, and depending on how low they go your crops could take a hit. But that’s the chance we all take. Or, said another way, that’s gardening.