Fruits may need thinning for growth, flavor
Jun. 26, 2013
Fruit trees that were so full of blossoms this spring that they looked like giant snowballs foretell a heavy crop of fruit later this year.
Too much, perhaps, for the branches to support. And surely so heavy that next year's harvest could be paltry.
Some fruit trees are prone to a feast-and-famine cycle — a heavy crop one year and a light crop the next. My Macoun apple tree is one of the worst in this regard among the score or so apple varieties that I grow.
Fortunately, this tendency toward "biennial bearing" can be reined in.
BLAME IT ON HORMONES
Hormones produced in fruit seeds are to blame for biennial bearing. The hormones suppress flower-bud formation, which begins in fruit trees the year before the flowers actually unfold. So a heavy crop one year — and, hence, a lot of seeds — quells flower-bud formation that year, and flowering and fruiting the next year. In a year with few fruits, hormone levels stay low, so many flower buds are initiated and in the next year trees are a riot of blooms.
The way to thwart this feast-and-famine tendency is to reduce the number of fruits in a tree's "feast" year.
Pruning is one way to do it — cutting off some stems that would have flowered and gone on to bear fruit. The time for pruning most fruit trees is past, though; it was back in late winter and early spring, before growth began again.
Pruning, of course, has effects beyond those on biennial bearing, and each kind of fruit tree has its own pruning needs. Still, as you prune to open a tree up to light and air, and to control its size, you are also removing potential fruits and seeds. And shortening branches puts remaining fruits closer to the trunk, where they are less likely to break a limb.
But pruning alone is generally not enough to get a fruit tree out of a bad habit. Now is the time to start looking over your trees and "thinning" — that is, removing — excess fruitlets. Focus your energy on larger fruits, such as apples, pears and peaches, because thinning would be too tedious — and has little effect — on small fruits such as cherries and small plums.
TAKE MATTERS IN HAND
The sooner you begin thinning, the greater the benefit next year, especially with apple trees. I use my thumbnail or a pointy pair of flower shears. If you have a lot of trees, you might opt for more labor-saving methods, such as blasts of water from a hose or batting the flowers with a piece of hose slid over the end of a broomstick. Many commercial orchardists thin their fruits with chemical sprays.
No need to complete all the fruit thinning in one session. Ideally, do it in two waves. The first is after fruits begin to form. The second is right after June drop.
After carrying extra fruitlets to get it through spring frosts and other early-season calamities, a tree gives a sigh of relief that danger has past, and decides it's OK to shed some fruits. Once that happens, look over your trees and put a few inches of space between each developing fruit, selectively saving those that are largest and most free of blemishes.
Fruit thinning has other benefits, too. It reduces pests, such as codling moth — the "worm" in an apple — because Ms. Codling prefers to lay eggs in apples that are touching each other.
Fruit thinning also lets the tree pump more energy, which translates into bigger size and better flavor, into those fruits that remain.
If you grow Asian pears and want to grow good-tasting ones, be especially bold with fruit thinning. These trees tend to bear heavily, and without bold thinning, the fruits are almost tasteless. Put a few inches between one fruit and the next, and their taste will be ambrosial.