Plants already exposed to cool temperatures will be more resistant. Within our own properties we can find variations on different sides of the house, under trees, on south or north facing slopes, or low lying areas. Cool air settles at the bottom of slopes because it is heavier than warm air. Frost pockets will then form in valleys where cool air becomes trapped. Hilltops are also susceptible to cool temperatures.
Hillsides often remain frost free until a more severe frost occurs.
The two most common methods are covering to keep the plants warm or to warm the plants by sprinkling with water. Covering is the most effective for most people. Covering plants the night before with a sheet, blanket, or tarp will trap the warmth from the soil over the plants thus preventing freezing. This type of covering will usually protect plants when temperatures drop into the upper 20's. Plastic used as a covering usually doesn't work as well as the other coverings mentioned.