Soil Temps -Late Planting is Best for Home Gardeners

 

Home gardeners often plan to transplant seedlings after May 12th, the last estimated frost date for our area. More important than a date on the calendar is soil temperature. This year gardeners need to wait to allow the soil to warm up and the low air temperatures in the foreseeable forecast are consistently in the fifties or warmer.

"Soil temperature is a factor which few of us consider important enough to check before planting yet it probably is the most important factor affecting … seedling growth,” writes Dr. Jerry Parsons, Texas Extension Horticulturist. Warm soil allows plant roots to grow out into the bed quickly. planting yet it probably the most important factor affecting … seedling growth,” writes Dr. Jerry Parsons, Texas Extension Horticulturist. Warm soil allows plant roots to grow out into the bed quickly.

For the best start to the garden season, plant vegetables in the garden when the soil temperatures are best to do so. Plants are sensitive to temperature both above and below ground. If the soil temperature is not right transplants just sit there, biding their time until it warms up. This affects root development and can stunt growth throughout the growing season. Cool temperatures can also invite rot.

Tomatoes, one of our favorited homegrown summer crops,  are heat loving—not only should they not be planted in the garden until after danger of frost, it is best to wait until the soil temperature is warm. Memorial Day is the perfect time to plant tomatoes in much of Pennsylvania. If you plant too early, tomatoes will languish in the cold and may die during an unexpected frosty night.

During the week of May 11, 2020, in Fayetteville, Pa., the soil temperature in a sunny, raised bed was only 50° F. Soil temperatures will vary among different areas in a garden and between different yards. Soil in sunny areas and raised beds will warm the quickest.

Cornell University in Ithica, NY, publishes an up-to-date soil temperature map for the East Coast.

Use a soil thermometer and take the temperature at 2-3” deep around 10 to 11 a.m. Temperatures vary during the day with the lowest soil readings just after dawn and the highest in mid-afternoon. It is best to get a consistent reading over a period of four to five days.

The best temperature for transplanting local warm season crops is 60° to 65° F. These include tomatoes, peppers, cucumbers, cantaloupes, watermelons, pumpkins, and squash. Beans can go in at 55° to 60° F. but okra needs 70° F. or more. Penn State Extension Planting and Transplanting Guide.

~ Carol Kagan, Master Gardener

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