Thursday, May 28, 2009

Thinning the Home Fruit Trees

As a relatively new fruit tree owner (last 2 years) I am trying to keep up with everything that should be done to the trees. This came in my email last week about thinning the fruit on your trees. I thought it was very useful and thought I would share, since it is time now to thin!! It is very hard for me to pluck those little fruits off when I have been so patient to get them.

Utah Pests’ Tree Fruit Advisory, 5-20-09 Page 3

University of Arizona Extension

Residential Growers: Thinning the Home Orchard

Fruit trees must like their job, because when left to their own devices they often produce more fruit than they can handle. Then, home gardeners are left wondering why their fruit aren’t as big or as sweet as those found in Utah’s farm stands and farmers markets. The solution to this problem is in proper pruning and thinning to keep a balance between fruit growth and tree health.

Why thin – The objective of thinning is to balance supply with demand (leaves per fruit) and in the case of apples and pears, to prevent or at least reduce biennial bearing. The goal is to have fewer fruit in favor of larger size, sweeter flavor, and a crop every year.

Supply and demand - For fruits to grow large and sweet, they require lots of energy in the form of carbohydrates. Maintaining a healthy root system and producing adequate new shoots and leaves also requires carbohydrate energy. This energy all comes from photosynthesis in the existing leaves. Too many developing fruits competing for the carbohydrates supply of a limited number of leaves result in lower fruit quality (smaller size, less sugar), weak shoot and root growth, and declining tree health. In the case of apples and pears, this energy drain in combination with plant hormones coming from the developing fruit, signal the plant to produce less flower buds for the following year.

Alternate cropping – Flower buds in temperate fruit trees begin their development the season before they open. For apple and pear, this starts 3 to 6 weeks after bloom. Peach flower buds begin to form 2 months after bloom. The presence of developing apple and pear fruitlets will prevent the short side-shoots known as spurs from initiating flower buds for the next year. If too many spurs set fruit in a given season, then there will be few or no blossoms the following year. This situation is known as alternate cropping or biennial bearing.

When to thin – Most fruit trees will partially thin themselves through natural fruit drop. However, this comes after a lot of energy is wasted on the extra fruit, and after the chance for improving return bloom has past. For best results, apples should be thinned when the largest fruits are between ½ and ¾ of an inch in diameter. Thinning late will help fruit size, but return bloom will be compromised. Peaches and other stone fruits should be thinned when fruits are ¾ to 1 inch in diameter. Stone fruits do not typically suffer from biennial bearing, but waiting too long wastes the plant’s energy and the opportunity to get the largest, sweetest fruit possible.

How to thin – When thinning, pick off the smallest fruits as well as any that are misshaped or damaged. Then adequately space the remaining fruits. Peaches, nectarines and other stone fruits should be spaced out 3 to 5 inches along a shoot. If the trees have not been properly pruned to reduce the amount of fruiting wood, additional thinning may be required to prevent a heavy crop from breaking limbs. To achieve the large sweet peaches that we all enjoy, a moderate-sized peach tree should only produce 100 to 150 fruits on the entire tree.

Apple blossoms come in clusters of five or six and, when pollination conditions are right, may try to produce three or more fruits on each cluster. For best results, apple clusters should be thinned to one fruit, and fruiting clusters spaced 6 to 8 inches apart.

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