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Wally Peck/Master Gardener: Questions on apple tree yields

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Why is there no fruit on my apple tree this year? This is a common question with a complicated answer. I am going to paraphrase an excellent article from the Extension office at Penn State University that clears up some of the mystery of apple trees.

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One of the problems apple trees have with yield is improper vigor. That means both too much and too little. Trees that spend their energy producing twigs and branches do not put their energy into fruit. Also trees that are over pruned are stimulated to grow more branches and less fruit. Fertilizing the grass next to an apple tree can produce too much growth. If there is a question as to the fertility of the soil they are planted in, get a soil test.

Frost damage is a common problem, especially here in the north where we get late frosts after the flower buds have formed. Temperatures colder than 29 during bloom will keep fruit from forming. Also, early spring when the buds are just starting to swell is a critical time as well. A hard freeze at this time will also damage the buds. A solution here is to only grow later blooming varieties. That is why Honeycrisp is questionable here.

In addition to spring frosts, extreme winter temperatures December through March can also damage potential buds. When we have a January or February thaw followed by extreme cold, you will see buds in the spring that do not open. We are at the mercy of the weather on this one; however, planting in protected areas can help.

Pollination is the third reason apples do not bear fruit. Cross pollination is necessary for fruit formation so two different varieties must be located in the general vicinity of one another. Since honeybees, bumblebees and related species are the pollinators here, low numbers mean less fruit formation. If you use insecticides, don't expect much fruit because bees are affected greatly by any insecticide use, lawn chemicals included, even if spray drifts over from your neighbor.

Apples are affected by the effect of last year's crop. Since the flower buds are formed now for next year's bloom, not thinning your bumper crop of apples will show up next year. When the fruit is first forming in the spring two to four weeks after bloom, thin down to one apple per cluster and thin clusters to every 6 to 10 inches. It seems like a lot but it will result in fewer broken branches and better yield next year.

One last reason for low production is the application of carbaryl (a.k.a., Sevin) during bloom. It causes the fruit to drop. Keeping these things in mind you can better anticipate regular apple crop here in the north.

To find reliable information about vegetable gardening and other horticultural topics, go to the University of Minnesota Extension website at www.extension.umn.edu/gardeninfo Local master gardeners will also answer your gardening questions via a voice-mail service. Call 444-7916, leaving your phone number, name and the nature of your question. A volunteer master gardener will give you a call.

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