A ground frost is the formation of ice on the ground itself or on other objects such as trees. This is because their surfaces have a temperature below the freezing point of water. Sometimes, when the ground cools quicker than the air, a ground frost will occur without there being air frost.
A grass frost can occur when other surfaces – such as walls, paths, roads – don’t experience a frost, because of their ability to hold any warmth. It is possible for a grass frost to occur in late spring or even early summer when the risk of more wide-spread frosts has disappeared and is something that gardeners in particular need to be aware of.
Walking on Frozen Grass
Walking on your lawn on a frosty morning can damage the lawn, causing bruised grass that soon turns brown. The problem being that these footprint marks wont go until the grass starts to actively grow again – in the spring!
When you walk across a lawn, the individual blades of grass are flexible. They bend underfoot and soon recover without damage. However, frozen grass loses its elasticity and blades rupture or snap, resulting in brown, foot sized prints.
The frost makes the blade and crown or the grass brittle and unable to yield to the foot pressure so they crack. However, it may also be due to ice crystals being sharp. When you step on them you press the sharp ice into the cuticle of the blade (the top layer of the blade is the cuticle). Once the cells are ruptured the grass is damaged.