This winter provided some fascinating differences in soil temperatures among our roadside turfgrass mixture testing locations (Figure 1). Each site is equipped with a weather station that is collecting precipitation, air temperature, soil moisture, soil temperature, and electrical conductivity.
We found that Marshall, MN had only 8 days this winter where the soil temperatures at 2 to 3 inches was less than 32 degrees F, whereas our location in Brainerd (very sandy soil, little turf establishment) had 119 days with a mean soil temperature below 32 degrees F (Table 1).
Table 1. Number of days with mean soil temperature above and below 32 degrees F from September 28, 2018 to April 5, 2018. Note some locations have some missing data and not all had data collected up to April 5.
Days of soil temp >32F
Days of soil temp <32F
East Grand Forks
Snow depth at the research site in Roseville, MN was nearly nonexistent throughout January until late in the month when an inch or less was present, then in early February there was 8 inches and by mid-February there was nearly 3 to 4 feet of snow on the shoulder. By comparing the volatility of soil temperature between the two months you can see the buffering capacity that the snow layer provided. Also, notice how soil temperatures were slowly increasing when there was a thick layer of snow (Figure 2).
The weather data we are collecting can assist us in evaluating why some species or mixtures fail and others perform well along roadsides in different regions of Minnesota. If a thick layer of snow is insulating the ground it is very likely to stay warm and even get warmer. If the soil temperature remains warm then this could result in persistence of certain species that do not tolerate severe winters. For example, from previous research we have found that tall fescue is one species that is relatively less tolerant to low soil temperatures, so it may perform well at warmer locations, such as in Marshall (Figure 3) or Chatfield, MN.
Overall, the relationship between snow depth and soil temperature is one thing among many that influences the relative abundance of a species and this will assist us in recommending appropriate species and mixtures along roadsides for different regions of the state. This research is driven in part to reduce soil erosion and thereby enhance water clarity and quality, beautify our city roadsides, and ultimately save taxpayers money.