Margaret Lauterbach: The best ways to thin fruit

Special to the Idaho StatesmanJuly 4, 2014 

If the fruit trees in this valley are as laden as those in my yard, this will be a great year for fruit growers and state tax coffers. The problem now is thinning that fruit.

Why should we thin fruit? There are good reasons to thin fruit, even though we hate to do it after it has escaped killing frost, wind and bird beaks.

We must thin fruit for the sake of the tree. For one thing, fruit-heavy branches break, tearing bark and severely damaging the tree, and making it more vulnerable for disease. Bracing loaded limbs is only partially effective, since it's very easy for wind or a bump against the brace by animals or humans to dislodge it.

Another reason to thin fruit is to prevent the tree from going into a biennial bearing pattern. That is, bearing heavily one year, then very light crop or no fruit at all the second year. Some apple varieties such as Gravenstein are very prone to that. If you thin fruit, it's less likely to skip the following year.

Also, any tree can produce a limited amount of sugars, and if there's too much fruit on the tree for it to supply sugars, the tree may just abort the entire crop, almost ripe, but still stone hard.

After proper thinning, the remaining fruit should develop to maximum size and sweetness, since competition for sugars has been removed.

I prefer to wait until Mother Nature does some of the thinning for me, during the period known as "June drop." That means, though, that we'll be thinning fruit later than experts advise.

Some fruit that develops weakly or smaller than others is due to insufficient pollination. That misshapen fruit. for example, should drop during June drop. Just touching it usually is enough to cause it to fall. I then remove damaged or misshapen fruit before tackling the removal of too much good fruit. I also try to leave only good fruit on sturdy twigs, not the tips of slender twigs.

Apple trees have an efficient way of survival. They set clusters of blossoms, one larger than others known as the "king blossom." It's surrounded by other blossoms that open at different times, some perhaps killed by frost, others opening later. When you're thinning apples, if the "king blossom" fruit (in the center of a cluster) has survived, try to leave that one, removing others in the cluster.

Leave about 6 or 7 inches between fruits on a single limb. I find it useful to use a ruler to measure your hand spread between thumb and outstretched pinkie, then use that as a guide for thinning some fruits such as apples, peaches, nectarines and apricots so you don't have to guess or carry a ruler. Thinning apricots is a joke at my house, though, since squirrels have laid into every crop of apricots just before it's ripe to eat the "nut" in the pit, wasting the fruit.

European and Asian pears rarely need to be thinned, but if possible, remove misshapen, small or damaged fruit as soon as possible, then thin to about 4 or 5 inches. My Seckel pear tree is heavily loaded with fruit, but I don't intend to thin that unless I see strain in branches because the mature fruits are quite small dessert pears that some call "sugar pears."

European plum trees usually don't need thinning of fruit, unless the fruit produced is uncommonly small. Then, timely thinning should enable the tree to produce normal-sized fruit in future years. Japanese plums, though, are notorious for heavy bearing, and should be thinned to at least four inches apart.

You shouldn't need to thin cherries unless they're dropping undamaged fruit. Any spur should only bear about ten cherries.

Send garden questions to melauter@earthlink.net or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

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