Dealing with frost

I am interested in learning about practical methods to reduce the effect of local katabatic flow of air in making low lying areas cooler and more susceptible to frost. There are many references that cold air can be trapped in low lying areas and that landforms, hedges, windbreaks, embankments etc can affect the flow of cold air and hence the frost effect.
Most advice seems to be along the lines of "don't plant frost tender crops in hollows" or "plant in hollows later in the spring". Well if you have a property that has low areas there is no point in wishing it wasn't that way - you need to make the best of what you have.
Can anybody give me a reference to practical advice on how to use hedges, windbreaks etc to reduce the effect, by directing the cold flow away from the garden or crop?
Specificaly I am interested in how to diagnose the situation, to be able to find out to what extent cold air flow is affecting frost intensity on my property and secondly, if this is happening, how to go about reducing the problem where possible.
David
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On Sat, 22 Nov 2003 23:31:52 GMT, "David Hare-Scott"

I would try raised beds in the low areas, that would raise the crops up just a bit and into slightly warmer air.
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Landforms and embankments won't prevent frost forming in a low spot, though they may worsen it if they act like a dam, preventing the cold air flow escaping. So, if possible, give the cold air an unobstructed way out at ground level.
A light overhead canopy of winter branches on a tree, can make a surprising difference to soil temp below. The disadvantage is that in summer, the trees may deprive the plants below of light sun water and nutrients. A permaculture method is to grow crops between wide orchard rows. Otherwise, you can use fleece crop covers during late spring frosts and early autumn ones; or moveable cloches. Soil mulches of light airy material like straw or bracken will help a bit.

Come winter, you can do it by observation of how much white is on the earth or grass.Colder spots will show a thicker build up of frost; especially if its in shadow, it may lie there all day after higher areas have melted off. Much also depends on winter sun and shade, your latitude and the aspect of your garden and its surroundings. Here (56 N) the winter sun stays so low in the sky some areas behind hills etc get no sun until spring.
You could also put out margarine tubs equally filled with water at various points, then note which has ice, or which has the thickest ice.
Janet.
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