Thin that fruit

Flower & Garden Magazine, May-June, 1997 by Alice L. Ramirez

Harvesting large, luscious fruit from a backyard tree takes more than water, fertilizer, mulch and insect control. Thinning out the developing crop is essential, too. It should be done, if possible, while developing fruits are still small -- about the size of peas. An overloaded tree is an unhappy tree, potentially an unhealthy tree, and certainly one likely to produce an inferior product.

Thinning benefits many homegrown fruit crops: peaches, nectarines, apricots, plums, pears, apples, loquats, guavas, tangerines, grapefruit, cherimoyas, mangos, litchi, mulberries and persimmons, among others. The culling process enables a plant to put all its energy into the remaining fruit. The harvest will be smaller, but those left to mature will be larger, with a better flesh-to-pit ratio than a comparable but heavier harvest of unthinned fruit. The remaining fruit will also have better flavor. A tree is best able to develop the necessary sugars, and therefore sweetness, if it can concentrate its efforts into a smaller number of offspring.

Thinning also protects the trees' health. The weight of too many fruits can lead to overloaded limbs that break and fall to the ground. It happens in a random and uncontrolled way that usually tears bark, thus exposing the tree to fungus and insect attack. Propping up an overloaded limb may be a temporary solution, but it only Weakens your tree in the long run. If, due to overcrowding, air cannot circulate through the tree, fruit and leaves also become increasingly susceptible to infestation and pathogens.

Allowing a very young tree to produce and ripen fruit retards its growth. By completely removing anything a very small, young tree produces, you enable the plant to develop the strength it needs to grow, ward off problems and sustain good harvests later on.

Some fruit gardeners also notice in their trees a tendency toward alternate bearing -- a heavy crop one year is followed by few or no fruits the next. Sometimes, but not always, thinning can alleviate this problem. A fruiting plant puts much energy into producing and ripening its offspring. A heavy set demands a great expenditure of vitality; afterward, the tree needs to recuperate. If left unthinned during a heavy-bearing season, it might produce a large number of smallish, inferior-flavored fruit, followed one year later by almost no fruit. Some species are naturally prone to be alternate-bearing, and there is little the gardener can do to change them. Even in these cases, however, excess fruit should be culled out to improve the quality of the harvest and general plant health.

Nothing is more discouraging to fruit gardeners than the dreaded "June drop." Under the stress of summer heat, trees can let go of all or most of their fruit. They do this spontaneously if the set has not been thinned. (The Japanese or "kaki" persimmon, Diospyros kaki, is particularly susceptible to this problem. It is not unheard of for a gardener to lose all but one or two fruits during a mass drop.) Take initiative early in the season to unburden a tree of its excess load to prevent the worst from happening.

A close inspection of early fruit set will reveal little green nubbins of varying sizes, indicating differing stages of development. In order to spread the harvest over a longer period of time, cull the immature fruits so that some remain in each of the various sizes. Doing so will prevent the urgent problem of what to do with 80 pounds of peaches, apricots or nectarines that all ripen simultaneously.

Loquats (Eriobotrya japonica) are an exception in that they should be thinned during flowering rather than the early fruiting stage. Lop off every other flower cluster, taking care to leave quite a few toward the top of the tree; these topmost fruits become the "fruit tax" that will be collected by birds. Experience has shown that if you leave some fruit up high, the feathered bandits are less inclined to peck holes in the fruits below -- those within easy human reach. Thin kaki persimmons during the flowering stage, too, or at least when the fruit is still pea-size.

When it comes to large-fruited species such as apples, pears or kaki persimmons, you are allowing your tree to bear too heavily if you can touch two immature fruits with one hand. On trees or bushes bearing small fruits such as strawberry guavas, loquats or mulberries, thin down enough to fit a thumb between fruits.

Many of these smaller fruits grow in clusters. A shortcut for those unwilling to fritter away an entire afternoon thinning out small fruit is to clip off entire bunches using scissors or small pruning shears. This method offers the same good effect as thinning individual fruits in terms of improved size and sweetness, but with far less work. A gardener who follows these spacing rules will be able to harvest the largest fruit possible, up to the plant's genetic potential.

Sunscalding can ruin the appearance of fruits such as persimmons or loquats. When thinning susceptible species, cull from the outside of the tree so that the ones remaining ripen farther inside where foliage will shade them. The fruits of other species, such as peaches and many varieties of apples, need exposure to sunlight in order to color up. Remove excess fruit from inside the tree -- those shaded by leaves and therefore not positioned where they can ripen fully -- in order to let the survivors on the outside develop the proper blush.