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FRUIT TREES: THINNING FRUIT [continued]

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  MG Manual Reference
Ch. 11, pp. 23 - 24

[Care: fertilization | thinning | pollination | irrigation | pruning ]

IRRIGATION Top

Irrigation is essential for the production of fruit in the arid desert environment of Arizona. Water can be applied with many different methods. The most common method is the use of a garden hose delivering water into a basin dug around the drip line of the tree. Basin irrigation is an excellent way to irrigate fruit trees but certain principles need to be followed. Make sure the basin extends about 2 feet beyond the drip line of the tree. Do no allow water to contact the crown of the trunk Many are beginning to utilize drip and micro-sprinklers as a way to save water. All of these methods are effective. The key to successful irrigation is the application of the right amount of water at the right time. For the amateur this is easier said than done. In general, newly planted trees need frequent shallow irrigations. They should be watered about once every 7-10 days once they have developed new leaves. Do not irrigate transplants until leaves begin to develop, then apply small amounts of water as needed.
General Irrigation Guidelines for Fruit Trees

Method Remarks
Basin Infrequent but generous amounts of water
  7 - 14 days depending on soil and temperature
  Basin should extend 2 feet beyond drip line.
Drip Frequent
  3 - 5 day intervals for several hours
  emitters need to surround tree and be placed just beyond drip line to encourage root growth
Micro sprinklers Frequent
  3 - 5 day intervals
  Wetting pattern should be 360 degrees extending beyond drip line of tree
Fruit trees have an effective root zone of about 3-4 feet deep from which they extract water and nutrients during the growing season. Most of the water and nutrients are extracted from the upper 12-18 inches. A typical irrigation requires that enough water be applied to penetrate the effective root zone. For mature trees the roots are wider than the width of the branches (drip line) in mid-summer. Water should be applied beyond the drip line. This will encourage lateral root development for young and developing trees. This is easily accomplished with basin and drip irrigation methods. The frequency of irrigation depends on the soil type to a large degree. Sandy soils will need more frequent irrigation than silty or clay soils. The main point in watering trees is to apply enough water to penetrate soils 2-3 feet. In basin irrigation water should be applied to a depth of 4 inches. Keep the trunk free from water to prevent disease. When using the basin method, water less frequently, but add enough water to penetrate deep into the root zone.
Drip and microsprinklers are being utilized in the home landscape and are excellent methods for watering fruit trees. Make sure emitters and sprinkler patterns cover just beyond the drip line. Drip and sprinklers require more frequent irrigations to be effective. Water every 3-5 days. During the hot summer season make an effort to deep water about once a month to leach salts and ensure deeper roots have available moisture. Don't forget to water during the winter. Tree roots continue to be active in winter months and need to be kept moist to prevent drying and freezing.
If there is some doubt about the watering schedule check the soil for dryness by using a soil probe. Use a 1/4 or 3/8 inch metal rod and push into soil after an irrigation. When the rod hits dry soil it will stop. Hence you know how deep the water has penetrated the soil. Check the soil (both wet & dry) for moisture by rubbing it between your fingers. This indicates a moisture level that is needed for optimum tree growth.
Trees do not use large amounts of water until the leaves are fully developed. Once leaves are fully developed in early to mid-summer with a crop of maturing fruit, water use will increase dramatically. Once fruit is harvested, water use will decline but trees still need water for maintenance and acclimation into dormancy. Continue to irrigate after harvest but not as frequently. In Arizona, frequent irrigation in spring can cause yellow leaves, root rot and waterlogging.
Mulching is certainly an option in growing fruit trees. Mulch such as tree bark, straw or hay, aids in preserving soil moisture resulting in less frequent irrigations.

PRUNING Top

There are many reasons for pruning fruit trees in the home garden.

•Pruning stimulates shoot growth by reducing the number of buds available for growth.
• Pruning is a dwarfing process and can be used to control tree size.
• Pruning improves tree structure.
• Pruning thins the crop resulting in better fruit quality.
• Fertilizer and irrigation recommendations are based on a properly pruned tree.
The best time to prune is during the dormant season. This is usually during the first several months of the year. The structure of the tree is readily identifiable and decisions are much easier.
Fruit trees should be pruned annually starting at transplanting. There are three stages of pruning during the life of a fruit tree. These three stages are: 1) transplanting; 2) training; and 3) mature. In order to correctly prune these trees in all stages there are certain factors and characteristics related to each kind of fruit. They are: desired shape and fruiting habit. The shape preferred by a kind of fruit will fit into 2 basic categories or training methods. These are: 1) central or modified leader or 2) open or vase shape. Basically all fruit trees can be trained to an open center with judicious pruning. However, the normal growth habit of some kinds of fruit allow easier training to the central or modified leader system. Also a tree trained to a central leader will take less space. Table 5 represents various tree characteristics to consider when training and pruning the various kinds of fruit trees. Fruit trees are much easier to prune if they have been properly trained and pruned annually.
The training process starts immediately after planting. If the new tree is an unbranched whip, cut it back to 30 inches above the ground. This will remove 1/3 to 1/2 of the tree depending on size. If the tree has branches, select up to four that form wide angles (45 degrees or larger) with the trunk. Space about 4-6 inches apart on the trunk in a spiral arrangement. Prune these back to 1/4 of their length and prune the top to 12 inches above top branch for development into a central or modified leader. For an open center or vase shape prune top off just above the top branch. The training of trees to either the vase or central leader is illustrated in Figure 4.
Table 5. Growth and Fruiting Characteristics of Fruit Trees Related to Training and Pruning

Fruit Growth Training Method Annual Shoots Spurs Productive Life of Spurs Pruning of Mature Trees
Apple Spreading Central or Modified Leader Some Most 5 Years Very Light
Apricot Upright, spreading vigorous Modified Leader or Open Center Some Most 3 - 4 Years Heavy
Nectarine Upright, spreading Open Center Most Some   Very Heavy
Peach Upright, spreading Open Center Mosts Some   Very Heavy
Pear Various Modified Leader Some Most 10 - 12 Years Very Light
Plum (Japanese) Various Open Center Some Most 6 - 8 Years Heavy Thinning
Cherry, sweet Upright Modified Leader of Open Center Some Most 6 - 8 Years Light Thinning
Cherry, tart Spreading Modified Leader Some Most 3 -5 Years Very Light
Persimmon Spreading Modified Leader All     Light Thinning
Plum (European) Upright Modified Leader Some Most 6 - 8 Years Light Thinning
Quince Spreading Open Center All     Light Thinning
Walnut Upright Modified Leader All     Light

Figure 4.

Open Center
Open Center

To train trees to an open center, choose two, three, or four shoots to form main scaffold branches the first winter. Remove or severely head all others. Choose one or two more the second season. Scaffold branches should be at least eight inches apart on the trunk for a strong tree structure. Four main scaffold limbs evenly distributed around the trunk are enough; a fifth limb crowds.
Central Leader
Central Leader

To train trees to a central leader, choose a vigorous shoot high on the tree the first winter after planting. Cut off the top inch to stimulate branching if it is two feet long or longer. Head all other vigorous shoots more severely. Repeat the process in the following two seasons so that no side branches become vigorous enough to compete with the central leader.
Pruning mature trees is a very relaxing activity and provides a strong sense of accomplishment. When dormant pruning mature trees follow these general principles:
• Remove any dead or diseased wood.
• Remove broken limbs -- cut back to where limb originally began growth.
• No two limbs should touch one another. One should be removed.
• Watersprouts should be removed. These are upright shoots growing straight up from older limbs. These should be removed in the summer when possible.
• For central leader trees remove strongest growing limbs and leave weaker ones. This evens out the growth and leaves the more productive buds.
• Remove parallel limbs. These are two limbs in the same plane. The upper limb is shading the lower limb. Leave the one in the best position.
• Prune annually.
• For an open center (vase) trained tree, leave some strong one year wood on outer edges of canopy for future small shoot development. Always clean out center of watersprouts.
• Remove any root suckers, those that grow from the rootstock. They may be growing up through the soil from the tree roots. Prune them out at any time.
• When pruning large overgrown, neglected trees, never remove more than 1/3 of the branches in one year.
• A modified central leader tree has the central leader pruned back to a side shoot just below where the leader arises from. This is done annually to reduce vigor of the tree.


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