How is soil temperature important to plants?

Plants will not grow and seeds will not germinate if the soil temperature is too low. The biochemical reactions involved in growth and development are very slow when temperatures are low. Below 50 F (~10 C), most biological activity is essentially halts in most plants.

High temperatures in soils is not good, either. However, soils are poor conductors of heat and good insulators. So if the sun heats the soil surface to temperatures uncomfortable for most plants, the soil just a few of inches below the surface are much cooler. The plant can cool itself by drawing up water from those cooler depths.

In addition to the plant's needs for proper temperatures, soil organisms are inactive at low temperatures. Some of these organisms help the plant access nutrients, so when they are inactive, it will reflect on plant growth.