Plant Exchange Blog

With delayed spring weather this year, soil temperatures must be warmer to germinate most seeds. To find the approximate soil temperature in our area, the Mesonet at www.climate.sdstate.edu shows current soil readings for select locations around South Dakota. At Beresford, today’s bare soil temperature is 34 to 44 degrees F. The soil warms more slowly than average air temperatures. 

A soil thermometer reading 4-5 inches below the soil surface is a way to check soil temperatures yourself. The first seasonal episode of Backyard Farmer, a Nebraska public TV show, discusses when to plant vegetable garden seeds. The chart below is a general guide. The back of the seed packet information is more specific.

Garden Vegetable Seed Germination Temperatures

The soil temperature for planting vegetables:

40° F or warmer: Lettuce, kale, peas, spinach.

50° F or warmer: Onions, leeks, turnips, Swiss chard.

60° F or warmer: Broccoli, cabbage, cauliflower, carrots, beans, beets.

70° F or warmer: Tomatoes, squash, corn, cucumbers, melons, peppers.

The seed germination temperature is often much warmer than the plant’s growing temperature. Once established, many plants can handle much cooler air temperatures if the soil is warm enough. 

Whipsaw spring temperatures are one reason some begin transplants indoors. Set them out when spring temperatures have warmed, and this region’s April 27-May 3rd average frost date has passed. Local nurseries and garden centers sell transplants as an option.

Flower seed packets often stress planting seeds in the garden soil after the last frost.

A couple of garden TV productions in the region provide information.

Backyard Farmer, from the Department of Agronomy and Horticulture, University of Nebraska-Lincoln, has begun weekly hour Nebraska public television shows on Thursdays at 7:00p.m. or Saturdays at 10a.m. or may be viewed online from the website or at convenience later on YouTube.

Prairie Yard and Garden is a 30-minute South Dakota Public Broadcasting show that features gardens in the Upper Midwest. It airs at 3:30 on Saturdays or online at www.pioneer.org. Past video topics are on the website.