Can you determine if there is going to be frost on the ground in the mornings in advance? I have noticed that sometimes on 25 degree mornings there is frost on the ground and other mornings when its 25 degrees there is no frost. This information is important to me because I work at SAS Soccer Park and we do not allow people to use our athletic fields when frost is visible because it will kill the grass.
Posted February 21, 2007
On the other hand, if the temperature is 25, as in your examples you mentioned, there may be no frost if the air is very dry and the dew point at grass level (also called frost point in sub-freezing conditions) remains at least a few degrees below the temperature at that same level. This situation, in which the temperature at ground level is well below freezing but no frost is present, is called a "black frost" and I'm not sure there is any reason to let anyone walk on the grass under these conditions if they are not allowed when frost is present. In other words, the actual temperature at ground level is more critical than whether frost has formed. In fact, when frost does form, it can be somewhat beneficial because the deposition of ice onto the grass releases latent heat into the blades and the air just above them that may prevent them from getting even colder. I suppose there could be a mechanical damage issue with the external ice crystals being ground into the blades when someone walks on them, but I don't know enough about turf health to know if that's the reason you prohibit walking on the grass when frost is there.
The NC State Extension Service has some excellent references on frost, among other weather impacts to horticulture, available online at