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Tuesday, October 30, 2012

When and How Do You Prune Pine Trees?


Q. I know you prune fruit trees when they're dormant, but what about pine trees and other conifers? Mine get a couple of growth spurts a year and I didn't know if there was a "better" time for pruning.

Pine tree candles.
A. Normally the decision to prune involves two pieces of information; when does it start growing for the season and if it has flowers or fruit that we value, we would normally prune after it finishes flowering or fruiting.

            In the case of pine trees that grow well in the temperate climates (those climates which have distinctive four seasons) we always default to the winter season for major pruning. So the normal time to prune nearly everything is during the winter months.

            In the case of pine trees that grow in temperate climates this is also the case. If we were talking about tropical pine trees (not in Las Vegas) then we would time or pruning to its normal season for dormancy which is the dry season.


Pine tree thinning to reduce blowover from high winds
and the subsequent loss of branch taper or caliper.
This practice can lead to branch breakage which it did
(see my other post on this blog). It is best to selectively
remove entire branches rather than lateral branches along
a major branch.
            An exception to this is a technique of pruning pine trees that encourages dwarfing and increased density of the canopy. This is a technique called “candling”. Candling is done when the new growth coming from the ends of the branches is about 4 to 6 inches long. This new growth as it is emerging resembles a candle.

            Candling is done with your fingers and simply breaks the new growth as it is emerging in the spring. Usually we break the candle in half, we never cut the candle. Cutting the candle with a pruning shears causes the tips of the needles, which are cut in the process, to turn brown. This is unsightly.

            By breaking the candle in half we cause the buds at the base of the candle to grow and instead of getting one branch to continue growing we may get three or four. These three or four new shoots will not grow as long as the single shoot we removed.


Pine tree thinned to reduce "sail" on the canopy resulting
several years later in caliper loss in branch and subsequent
limb breakage (bottom center).
            This new growth remains more compact. Having three or four new shoots instead of a single shoot increases the canopy density.

A recent problem has developed in pine tree pruning. This is the idea of "thinning" the pine tree canopy to prevent blowover. In some cases on shallow soils with shallow, frequent irrigations, pine trees might not have enough root structure to support the tree in heavy winds. With gale force winds these trees blowover damaging property.

One recent practice by arborists has been to offer "thinning" of the canopy by removal of branches thus reducing the "sail" effect of the canopy during high winds. This sounds good but you have to be careful WHICH branches are removed in the pruning process. If lateral or side branches are removed along a stem or branch, this might cause a decrease in the strength of this branch due to a future loss of branch "taper" or caliper. This decrease in strength due to a loss of branch taper can lead to breakage and dropping of these weak branches.

I posted about this earlier in my blog.
http://xtremehorticulture.blogspot.com/2011/09/problem-with-pruning-pine-trees-so-they.html

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