Fall frost

Lucky for everyone involved, we get to deal with frost twice per year: spring and fall. Dealing with the frost and the subsequent delay differs slightly between spring and fall.

Spring frost occurs as everything is coming out of winter. The ground is very cold and the turf has spent months adjusting and hardening off to the cold weather. The turf’s ability to withstand frost damage is as high as it will get. Though it is still vulnerable, the natural defense of the grass has been built up through enduring the cold winter. None of this is true in regards to frosts that occur in the fall.

In the fall, the ground is not cold, which helps to make the first few frosts not as severe. But it also means that the turf is not yet ready to deal with the low temperatures. Because the grass is still adjusting to the cold, it is at its most vulnerable for damage. Luckily, because these initial frosts are not heavy, damage is usually minimal. Also, because the daytime temperatures and soil temperatures are still relatively high, the grass is usually able to grow out of any damage that may occur. Nevertheless, the early fall frosts are still a time to be very cautious and allow the turf to adjust to the cold.

The most crucial fall frost is the first heavy frost. This is the frost that makes everything look white when you look out on the course. We must be very careful with this frost because there is a high risk of damage. The plant’s defenses are just kicking into gear and the growth has slowed so recovery would be minimal.

The Grounds department has some strategies to deal with and help shorten the frost delay. But there is one strategy in particular that is not always available in the spring that is available in the fall. As mentioned, the soil temperature in the fall is still high. The soil is insulated and it takes much longer for the soil temperatures to change compared to air temperature. So although the air temperature may drop below freezing early in the fall, chances are, the soil temperature is nowhere near that cold. This has two implications. First, because the ground is not freezing, it means that we have not shut down the irrigation system yet. The ground has not become cold enough to freeze the water in the pipes so there is no worry of burst pipes. So we have the irrigation system at our disposal. Having irrigation water available means that we can “water the frost off” the turf. Basic chemical properties of water state that above 32 degrees Fahrenheit water is a liquid and not frozen. The frost on the turf grass plant is below 32 degrees. So the irrigation water is warmer than the frost on the plant and irrigating the frost will melt it or at least turn it to a slushy-icy mix. Seeing the slush on the plant versus frost, means that the plant is no longer cold enough to cause water molecules to freeze on the surface and create frost. Now the cells inside the plant are thawed too so the frost damage potential is nearly eliminated.

This does not mean that we simply turn on all the sprinklers on the course and declare the frost delay over. Timing of watering the frost off is still crucial. If the irrigation is used too early, when the air temperature is still too cold, the plant will thaw momentarily only to re-freeze. This is often the case in shaded areas. The coldest part of the morning is just at sunrise. The surface of the earth has been losing heat all night and morning, all the way until the sun starts to rise and begin heating the earth again. Once the sun starts warming the turf, frost can be eliminated quickly with only a quick watering. However, in the shade, where the sun has not had a significant affect yet, turning the irrigation will not provide the same response.

See you on the course!

Joe

jvillegas@bwrc.org