Lowest risk of frost damage: east, north, or south-facing?

General Fruit Growing
1

Which is the best slope on which to plant stone fruit in a frost-prone area?

I have heard people claim north, the idea being that there is not as much sun during the day so the trees stay dormant longer. Also south, to warm up the trees faster.

West-facing is the worst. You get no warmth in the morning, and then you get warmth in the afternoon to wake up the trees to make them more vulnerable.

So is east actually the best? Morning sun to dismiss the frost that tends to be maximal just before dawn. But then less exposure to the afternoon heat that can wake trees up.

2

Soil warms up last on the north side so trees should come out later in the season. trees will be less sensitive to frost if they come out later.

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3

Assuming you have a decent growing season and don’t need to risk waking up the trees too early, I vote for a north slope. Ideally the trees would get full sun when the sun is high in summer, but little or no sun when the sun is low in winter.

My premise is that cold temperatures don’t matter so long as the tree is fully dormant. So the major risk is that the trees get too warm in late winter and exit dormancy too early. The goal therefore is to keep them dormant as late as possible. Less direct sunlight in winter is better.

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4

The lowest temp is generally in the morning when the sun has little to no power to warm things up. A southern wall is going to be just as cold as a northern wall, when the sun peeks above the horizon at the coldest part of the day. You want to plant on the north side of a wall/house. This will keep more of the warmer mid-day sun off the dormant tree and generally slow advancement out of dormancy.

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5

There’s some additional factors to consider as well, assuming you are talking about a site in California. In the most common type of frost events we get here, cold air flows downhill and pools on the valley floor. Obstructions like buildings and windbreaks can prevent cold air from flowing through an orchard. Likewise, a slope with a steep angle will let cold air move through more rapidly than a more gentle slope. Third, there is an inversion layer, where warmer air sits on top of cold air. Somewhat counterintuitively, an orchard at a higher elevation can be 10 degrees warmer than one lower on a slope by being situated above the inversion layer in the thermal belt.

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