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Besides increasing fruit size, you need to keep trees bearing every year. Trees will set the fruit buds that will bloom in 2002 by mid-summer 2001. Thinning balances the fruit crop for this year with the bud production for next year. Trees produce only so much energy. They can devote the energy to fruit or buds. If too much energy goes to the fruit production this season, they form no blossoms for next year's crop. The trees go into biennial bearing and produce crops every other year. Many apple varieties are prone to this problem.
Young trees often set too much fruit. If they are not thinned, the energy of the tree goes into producing fruit at the expense of producing vegatative growth that will make a strong and viable tree. Remove the fruit from newly planted trees for the first few seasons to prevent this problem.
Thinning also promotes fruit color and quatlity. Many varieties have better fruit color and better taste when a heavy crop of fruits is thinned.
A final reason for thinning that will not be readily apparent until later in the season is to avoid tree damage. Every year many trees have sticks and boards propped under the branches to keep them from breaking. Many of them still split right down the center when the fruit load gets too heavy. Save the tree by properly thinning the fruit right earlier in the season.
The reasons for thinning are readily apparent now, but how to thin and when to thin is more difficult. Most fruit trees set far more blossoms than are actually needed to set a full crop of fruit. Some excess fruits must fall because there are simply too many.
The first drop occurs right after blossoming. Fruit that is not polinated does not develop and falls to the ground. This distresses many gardeners but is not as serious as it seems. If all the blossoms develop into fruits, it would be severly damaging to the trees. It takes only 10 to 20% of the blossoms to develop in heavy bloom years to have a successful fruit harvest.
The second drop is called the June drop. During this drop, many of the fruits fall because the tree is trying to regulate its crop. After this drop has occurred, it is time to do the final thinning by hand to insure a successful crop.
Excessive fruit set will ALWAYS reduce fruit size and quality. Removing part of the crop is the most effective way to improve fruit size. Separating fruit improves light distribution around the fruit thus improving the color. It also improves pesticide coverage reducing insect damage.
The earlier thinning is done, the more significant the influence on the fruit size. The later thinning is done in the season, the less it contributes to increased fruit size. Late hand thinning can help improve crop quality by grading out culls while they are still on the tree.
Space the fruit during thinning. On apples, each bud opens to reveal a cluster of five flower blossoms. The large central blossom is the king with four smaller ones around it. The king makes the larges apple and ideally only the kings would set fruit. Even then, many of those would also be thinned, leaving the fruit spaced about every 8 inches on the outside perimeter of the tree where they are exposed to sunlight. Thin pears the same way.
In years without frost and freeze damage, peaches set more fruit than the tree can support. Three to four weeks after bloom, when the largest fruits are the size of a quarter, thin so the remaining peaches are spaced every 8 inches. Fruit thinning allows the remaining fruits to develop optimum size, shape and color, and prevent depletion and breakage of the tree. Thinning plums is usually limited to the large, Japanese varieties that are spaced 4 inches apart.
It is more desirable to have the strength of the tree fo into moderate amounts of large fruit than a large amount of small fruit. From an economic standpoint, a bushel of large fruits is worth twice as much as a bushel of small fruit, so do not let too many fruits remain. For the best benefit, comlete thinning within 20 to 25 days after full bloom.
Hand thinning is the surest way of doing a good job of thinning the fruit. Damaged or poor quality fruit is removed in the thinning process. You can also use a piece of hose attatched to a stick to knock off fruit. This method is not precise but it is faster. Best results with this method are obtained early in the morning or late evening, when fruit stems are firm and crisp.
Chemical thinners are not recommended for homeowners. They are used with carefully monitored production practices and applied at precise dosages. Let commercial growers use these products unless you know exactly how to use them. If you don't, you may destroy your entire crop.
Do not fall prey to broken tree and little fruit sydrome this year. Get out in the orchard and remove the ecxess to insure a quality harvest this season.