Soil Temperatures



How does the soil temperature affect your landscape?

Soil Temperature is the factor that has the strongest impact on plant growth, and its transition into dormancy. Due to different regional climates, soil temperatures will warm and cool as a delayed reaction to the atmospheric temperature. The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree, F zones, with a total of 26 zones in the United States. In Iowa, we cover 3 different Hardiness Zones, 4b, 5a and 5b. Locally, Linn and Johnson County are in zones 5a and 5b, respectively, with an average annual minimum temperature of -20 and -10 degrees Fahrenheit.


Soil temperatures are measured at a depth of 4” below the surface.  The surface temperature of the ground will be cooler, or warmer than the measurement at 4” below-surface temperature, depending on the time of season.  In other words, at 4” below surface, the temperatures are warmer than ground levels in the cold season (winter) and cooler than ground levels in the warmer season (summer).

As seen in the map below, our homes in Linn County and Johnson County are currently sitting at a temperature in the range of 28 to 30 degrees.

3-4-15 Iowa State Soil Temperatures

Though temperatures in our region tend to fluctuate with drastic highs and lows, the ground temperatures maintain more of a gradual change as the seasons change.

How do the soil temperatures affect the turf?

In Iowa, the most common type of turf is comprised of cool season grasses.  Cool-season grasses are grass species that thrive in areas with cold winters and hot summers.  Sounds familiar, doesn’t it? These grasses grow best when temperatures are between 65-80 degrees F, which is why they do most of their growing in the spring and fall. The most common grasses are Kentucky bluegrass, perennial ryegrass, tall fescue, and fine fescue. You’ll often see these seeds blended together for different microclimates and uses, such as high-traffic areas or lawns with sun and shade.  This practice also offers a diverse turf stand to ward off diseases and pests that thrive in monocultures.

Here are some common characteristics of how soil temperatures affect cool season grasses on both the high and low end of the soil temperature spectrum:

Cool Season Grasses (all temperature measurements shown in Fahrenheit)

90° Shoot growth ceases.

77° Root growth ceases.

70° Maximum temperature for root growth.

60-75° Optimum temperature for shoot growth.

50-65° Optimum temperature for root growth.

40° Shoot growth ceases.

33° Root growth ceases.

20° Low temperature-kill possible if temperature subsequently drops rapidly below 20°F

See where last year’s soil temperatures were during the calendar dates from April through December in Cedar Rapids, Iowa last year HERE. That late April to late May timeframe was optimal for growth last year.  We’ll see what nature brings us this spring, and hopefully it’s a lot of GREEN!

Your local professionals at Quality Care, the Nature Care Company in the Cedar Rapids and Iowa City areas are happy to help with any questions you have.

Contact us today!

Cedar Rapids area: (319) 366-7822

Iowa City area: (319) 354-3108

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