In marginal conditions, it is the local topography more than anything else which dictates where frost is most likely to occur. Air becomes denser and heavier as its temperature falls and, on a clear night, where the ground is uneven, cool air tends to slide downhill, flowing into cold "pools", into so-called "frost hollows", rendering the ground beneath it unusually prone to sub-zero temperatures. The practised eye can easily identify such spots.
It is also possible to create a frost hollow artificially without realising it. A newly built wall at the bottom of a sloping garden, for example, may act like a dam to create a reservoir of cold air on its uphill side. Frost in such a garden will then be a much more frequent visitor than was the case before the wall was built - when the cold air would simply continue on its way downhill.
Perhaps it was of this that the appropriately named poet Robert Frost was thinking he when he wrote: Before I built a wall, I'd ask to know What I was walling in or walling out.
Other structures, however, can be used to guard against the frost. The frames and cloches often used to cover low-growing plants and seedlings in spring confer the twin benefits of increasing daytime temperatures within and protecting against frost at night.
In achieving the former objective, cloches work exactly like a greenhouse. Firstly the glass is more or less transparent to short-wave radiation from the sun and let the energy in, but it is almost opaque to the long-wave radiation emanating from the ground - and so traps the heat inside.
Secondly, since a relatively small volume of air is confined within the cloche and is not continually replaced by cooler air wafted by the wind from somewhere else, any heat which may be trapped inside accumulates efficiently.
In providing protection from frost, two processes are at work. Firstly, as we have seen, long-wave radiation from the ground is significantly reduced by a covering of glass, so the tendency for the temperature of the soil to drop dramatically on cold clear nights is much reduced.
Secondly, the fact that it becomes warmer under glass by day than it is outside means that the soil within, acting rather like a storage heater, must cool much more at night to reach the freezing point.
When a very severe frost is expected, the degree of protection can be enhanced if the glass itself is covered with sacking or some other convenient material to provide extra thermal insulation.