When to fertilize fruit trees: Tips from Oregon master gardeners

Horticulture -- U of M Varieties -- Tree fruits -- Apples -- #1

Established fruit trees don't need to be fertilized much besides annual compost, say OSU Extension master gardeners. Photo of Sweet Tango apples provided by the Regents of the University of Minnesota.

(Regents of the University of Minnesota)

When the fir needles are falling or your soil is getting too soggy, get the answers you need with Ask an Expert, an online question-and-answer tool from Oregon State University's Extension Service. OSU Extension faculty and master gardeners reply to queries within two business days, usually less.

To ask a question, simply go to the OSU Extension website and type in a question and the county where you live. Here are some questions asked by other gardeners. What's yours?

Q: I'm looking into fertilizing my fruit trees, which include apple, pear and peach, for better production, but I'm not sure when is the best time. I fertilized last year but did not get good results. The trees had a lot of new growth and not much fruit. When is the best time of year to fertilize? - Clackamas County

A: Your fruit production may have more to do with pollination than with fertilization. You don't indicate the age of the trees or whether fruit production was good in the past. If the trees are relatively young -- less than five years at your site -- it may be that they are a little too young to be producing a significant crop.

Both apples and pears benefit from having different varieties to help pollinate. I have one apple tree (there are other apple trees in the neighborhood) and two pear trees for precisely that reason. You can get the same effect with different varieties grafted onto the same tree.

It could also do with the population of pollinators. Our native mason bees are typically active for pollinating the earliest blooming fruit trees. See the Extension publication Encouraging Beneficial Insects in Your Garden for how to promote the population of these beneficial insects.

Pruning practices can also affect fruit production. Read Training and Pruning Your Home Orchard for information.

If these are established trees, you really shouldn't have to fertilize much besides annual compost.

You didn't say the type of fertilizer you used, but because there was "green" growth, I'm going to infer that the fertilizer was higher in nitrogen. Most fertilizers will list the macro-nutrients of N-P-K.

If the first number is larger than the other two, it will promote vegetative ("green") growth more than promoting bloom/flowering. To promote the latter, look for the middle, P for phosphorous, to be slightly larger than the first number.

You can review Fertilizing Your Garden: Vegetables, Fruits, and Ornamentals for more information about using fertilizers in your home garden.

It may be worthwhile to get a soil test now to determine macro- and micro-nutrients in your soil. Before applying fertilizer, we would recommend getting a soil test done for the areas in which your trees are located. Locally, this can be done by A & L Western Agricultural Laboratories. - Sara Running, volunteer OSU Extension Master Gardener

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