In northern climates, it is not uncommon for a lawn to be covered in frost on a cold fall morning. And if you walk across the lawn when it's in this state, you could be causing serious damage to your grass. Here's how frost affects grass, as well as some things you can do to minimize its impact.
How Frost Impacts Your Lawn
Frost typically occurs on cold, clear nights when atmospheric conditions cause objects, including grass, to become colder than the surrounding air. Depending on the conditions, frost can be light and scattered or heavy enough to kill annual plants and cause perennial plants to go dormant.
Grass blades move water through them for nourishment, but this moisture can freeze inside the grass during a frost. Water molecules naturally expand during the freezing process, so plant cells can be damaged as the moisture expands and ruptures cell walls. However, a light frost generally doesn't freeze the ground; your lawn's roots will remain above the freezing point. As a result, you might have some grass blade damage after a light frost, but the roots have a chance at healing the damage as the grass continues to grow.
Frost over several nights can lead to visible signs of damage, depending on the grass species. For example, Bermuda grass can acquire a brown, patchy appearance and will die relatively quickly if warmer temperatures do not return. In contrast, St. Augustine grass will develop a brown, yellow, or even purple hue in the damaged areas. You can try reseeding any damaged areas once spring arrives. The dead grass will eventually become thatch that nourishes the soil below as the new seeds germinate and grow.
Why You Should Avoid Walking on Frozen Grass
When a lawn is frosted, the grass blades are literally frozen. Any activity on the lawn while it is frosty, such as walking on it or mowing it, can break the grass blades. When a heavy object presses on frozen blades, the expanded water molecules slice through the grass and cause significant cellular damage.
You can see the results of the damage when the blades produce a white or beige hue from being crushed along with the icy frost. The lawn will recover eventually, but it might not fully bounce back until the following spring.
Rain delays are common in sports, but a "frost delay" can help prevent damage to a golf course or baseball field during cold weather.
How to Minimize the Effects of Frost
One of the most practical ways to prevent light frost effects across your lawn is by watering the turf in the evening. Deep watering allows the moisture to evaporate slowly overnight. This evaporation creates friction and heat around the grass blades. As the night air temperature drops below freezing, your grass will still have a slightly higher temperature due to the evaporative heat processes. Thus, your grass won't reach the freezing temperature necessary for the water molecule expansion that causes damage.
If your lawn does freeze and you need to walk on it or mow it, consider waiting until the sun is high enough to melt the frost. To speed up the process, do what turfgrass managers do at golf courses: Use a sprinkler to melt the frost with warmer water. If the weather is so cold that a sprinkler is not an option, then it's probably too cold to mow at that time as well.