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Eager for spring planting? Let soil temperature guide you

Keep an eye on the forecast and consult the soil temperature to find out when to plant this spring.
Keep an eye on the forecast and consult the soil temperature to find out when to plant this spring. File photo

Spring starts Thursday, and daylight saving time already has us feeling it. Wondering when you can start planting?

Hardened-off cabbage, broccoli, cauliflower and onions can withstand temperatures near 20 degrees without being killed, Ward Upham of K-State writes in the Horticulture 2014 newsletter. “Lettuce plants are not quite as tough but will be OK if exposed to temperatures in the mid-20s. Don’t hesitate to put these plants out soon if extreme cold is not forecast and the plants are hardened off.”

Hardening off means acclimating plants to outdoor conditions. The process usually takes about a week Upham said: Start by placing plants in a shady, protected location and gradually move them into a more exposed, sunny location as the week progresses.

In addition to keeping an eye on the forecast, you can use a soil thermometer to check conditions below ground, or check the weather page in The Eagle every day at the back of the Local & State section under “Farm & Garden” for the soil temperature.

“Plant your cool weather crops when the soil warms to 35 or 40 degrees. Go with your warm weather crops when it gets up to 55 or 60 degrees,” said Shawn Olsen, an agriculture professor with Utah State University.

St. Patrick’s Day, which is Monday, is also seen as a potential planting date for potatoes. Make sure the minimum soil temperature is 40 degrees.

Also pay attention to the variability of maturity dates listed on seed packets and plants, Olsen said. “Many radishes, for example, mature in 30 days.”

Microclimates play a large role, Olsen said.

It makes a difference whether “you’re planting on the top of a slope, the middle or on the bottom, because cold air tends to go down,” he said.

Anything that is heat-absorbing or gives off infrared radiation at night is useful. That means planting alongside a house, stone walls or outbuildings.

“Generally speaking, the south side of a building is warmer; the north side cooler,” Olsen said. “Learn to take advantage of that.”

Loose, sandy soil with a sunny exposure will dry early, he said, while “wet, packed soil takes longer. Your plants will just sit there.”

Keep row covers handy to throw over plants if the weather takes a turn for the too-cold. March 29 is the average last day of a hard freeze in Wichita, and April 11 is the average last day of a frost (32 degrees).

Fertilize before planting, working the fertilizer into the soil, Upham said. Have a soil test done to be sure of what your soil needs, or use a vegetable fertilizer at the suggested rate, he said.

After the plants are planted, Upham recommends watering in with a root stimulator or transplant solution to water in after the plants are set. About 1 cup of solution per plant is sufficient.

Contributing: Associated Press