October 10, 2008

Dirt Gardener: Summer Pruning Has Its Adherents

By Buzz Bertolero

Q: My husband has read that fruit trees could be pruned once they stop producing. Is this true, or do we have to wait until all the leaves fall off to prune our plum, peach and nectarine trees?

A: The short answer is you don't have to wait for the leaves to drop to prune deciduous fruit trees, but this long-established norm is changing.

The winter months are still an excellent time to prune and shape, as the structure of the tree is easier to see without all the foliage. But dormancy starts many weeks or months earlier.

Dormancy is defined as "a period in which a plant does not grow, awaiting necessary environmental conditions such as temperature, moisture, and nutrient availability." It is a state of quiet inactivity. During the growing season, there can be several rest periods where plants are inactive between flushes of growth.

In the Bay Area, the growing season is March through the first Sunday in November, give or take. This happens to correspond with daylight saving time. Plums, nectarines, peaches and other deciduous fruit trees have only one flush of growth each year -- figs are an exception.

In some years, it's not uncommon for fruit trees to have a second set of flowers and set a secondary crop. This occurs when we have cool temperatures followed by above-normal temperatures late in the year. This secondary crop rarely matures. So once the flush of new growth has matured and the crop has been harvested, dormancy begins.

Fruit trees are fertilized before and during the flush of growth. Once the rainy season concludes, they're watered through the heat of the summer and, except for those trees with a maturing crop, you should stop watering them shortly after Labor Day. An established fruit tree is watered thoroughly once every 14 to 21 days. Apples and pears are the exception. Once the heat of summer has passed, water stress is no longer an issue.

One of the primary causes of borers and root rot problems in fruit trees is excessive moisture. Summer pruning is used to control the size and shape of an overly vigorous tree. It may also be used to thin the fruit or remove water sprouts and other undesirable wood.

Personally, I wouldn't prune severely the day after harvest. Instead, I'd wait until after the middle of September. If you remove too much of the foliage, the scaffolding and secondary branches are susceptible to sunburn, which then leads to other problems.

With apricots, fall pruning is being strongly recommended to prevent Eutypa dieback. Eutypa is an airborne disease that enters through the pruning wounds. It takes a couple of weeks for the pruning wound to seal. Cool and moist conditions are the chief contributor to this disease that doesn't show up until the following summer.

Here is a Web site that promotes summer pruning: www.davewilson.com/homegrown/BOC_explained.html.

Buzz Bertolero is executive vice president of Navlet's Garden Centers and a California Certified Nursery Professional. His Web address is www.dirtgardener.com., and you can send questions to [email protected] or 360 Civic Drive, Suite D, Pleasant Hill CA 94523.

Originally published by Buzz Bertolero, Oakland Tribune correspondent.

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