The soil temperature in which your grass lives greatly affects the speed at which the grass grows.
A warmer soil contains more energy. More energy available enables chemical process driving plant growth to work faster and more efficiently. This means grass can make food quicker (through photosynthesis) and therefore grow faster. There is a direct correlation between the temperature of the soil and the speed in which grass grows.
One of the main chemicals to cool season grass health is water. If the soil is cold or frozen, water cannot move through the grass plant easily and so growth slows or even stops. Conversely, if the soil temperature is too hot, water is lost too quickly through evaporation. This dries out the plant and its growth also slows.
The optimum range of soil temperature for cool season grasses is between 18-24 degrees Celsius. Grass will still grow outside of these temperatures, just not as quickly.
Different processes in the plant are activated at different temperatures. This table shows the soil temperatures which are needed to maintain good grass growth.
Grass Plant Growth Rates
|Soil Temperature||Grass growth pattern||Result|
|1 °C||Root growth stops||Cold stress|
|5 °C||Shoot growth stops||Cold stress|
|18-20 °C||Optimum for grass roots||Ideal temperature|
|15-24 °C||Optimum for grass shoots||Ideal temperature|
|25 °C||Root growth stops||Heat stress|
|32 °C||Shoot growth stops||Heat stress|
Soil temperature is not the same as air temperature
Soil temperature is not the same as air temperature. The earth acts like a giant radiator. It gradually absorbs the suns energy over time, and then releases it slowly. Air temperature can fluctuate dramatically as day turns to night and as the seasons progress. Soil takes a long time to change temperature.
In the spring, the soil is cold from the winter and can take a long time to heat up. This is why spring scarification and lawn repairing can pose problems due to the soil not having warmed sufficiently. Seed may not germinate quickly and grass growth can be sluggish.
In the autumn, the opposite is true. The air temperature maybe falling, but the soil retains a lot of heat. This helps seed germination and aids the grass in absorbing valuable nutrients from autumn fertilisation. Many lawns can continue to look green and lush well into autumn and early winter. Autumn is usually the best time for seeding and major lawn renovation work.
If you want to know how your grass is coping with the current climate in your then buy yourself a soil thermometer. Knowing the temperature of your soil will really help you provide the correct treatment for your grass at the right time.