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FRUIT TREE PRUNING

by Phil Mathewson

 

There are no hard and fast rules of pruning for growing fruit organically. However, by observing your trees with the following general pruning principles in mind, you can find the best way to deal with your orchard, whether you are a commercial orchardist trying to get lots of low cost grocery store quality apples into chain stores or a backyard orchardist with two trees looking for a bushel of good macs and maybe one or two for juice or pies. Ultimately, you will be responsible for your trees and no manual can guide your hand.

There are two main types of pruning: renovation and maintenance. A third type, summer pruning, is far outside the scope of this article.

When renovating, you are trying to convert an overgrown, diseased or damaged tree into a healthier, better managed tree. This is usually accomplished over a period of time rather than all at once, the intent being to redevelop the tree’s fruit-bearing potential and to increase its health.

When maintaining, you periodically prune to encourage regularity of fruit production and lower disease pressures. This need not necessarily be done each year.

There are some general points common to both types. Organic fruit management requires overall better disease control, more restricted growth and better air circulation than conventional fruit production. Stand back and look at your tree before you start. Get acquainted with its form; note the way the branches develop and overlap and the angle of their ascent. Think of your intent with the tree and try to remember what you know of its history. What type or variety of fruit tree are you looking at? What is the rootstock? All this information will help you in your task.

Different species of trees require considerably different approaches; a weak tree requires invigorating treatment, a strong tree the converse. You need to know your soil and assess your moisture supply.

Novice pruners should be aware that trees have their own way of growing, influenced by factors such as strong prevailing winds or a nearby rock shelf. Try to respect the tree’s wisdom. Don’t try to turn Albert Einstein into a ballerina.

 

Renovation Pruning

In most cases this will involve the hardier fruits such as apples, pears and European plums. The degree and type of problems encountered for each type of fruit will be different.

That badly overgrown fruit tree that you inherited with your property can be brought back. Apples are forgiving and can be pruned almost anytime. Their wounds heal quickly, callousing easily even at quite low temperatures. They do not readily sustain infections at wound sites. As a rule of thumb, though, unless you are doubly sure of the mildness of your winter, stick to February 15 onwards. For pears, European plums and sour cherries, shift that date to about three weeks later.

The act of pruning opens tissue, stimulating healing processes. Dehydration and further tissue damage can result under cold and low relative humidity conditions.

You will seldom have to resort to serious renovation pruning on peaches, nectarines, sweet cherries and Japanese plums. These and most apricots seldom live long enough to need renovation. A peach at 25 is old. Because these fruits winter-damage easily, some renovation is necessary within the normal course of maintenance pruning. For sweet cherries, apricots, Japanese plums and Japanese pears, prune after March 15. Peaches and nectarines deserve special mention. These genetically identical trees heal their wounds so slowly at low temperatures that they should be pruned only after temperatures have risen above 15 C. In most places in Canada, that means late May or early June. The above date guidelines are for southern Ontario; adjust accordingly for wherever you live.

Fruit trees don’t go wild when neglected, but they can undergo several types of changes that make renovation difficult. In tackling a neglected tree, you must first assess its problems. Observe your tree from a distance to see how it was originally trained. Older trees on standard seedling rootstocks were usually pruned to control their size somewhat; once left alone, they grow up with the new higher branches shading and eventually killing many lower ones. Some old apples, apricots and sweet cherries can reach impressive sizes indeed.

Pick out all the dead and dying branches, but try to avoid cutting into living tissue. That should be the limit of your pruning for the first year. Pay attention to the tree’s growth over the coming season; see how it progresses and what it tries to accomplish with that one burden gone. If you have already removed diseased limbs, watch for reoccurrence of disease and remove accordingly.

Plums will often be choked with a lesion fungus known as black knot. This problem is not systemic but its mycelia extend into the wood under the bark for some distance. Although plums covered with this fungus look incredibly ugly and about to perish, I have successfully renovated dozens of them even in so radical a fashion as to cut them down to a virtual stub. Cuts must be at least 15 cm below the lesion so as to remove all of the mycelium. Burn or bury all removed wood because the fungus is still living and will continue to produce airborne spores that can reinfect your tree or others. Ditto for sour cherries.

Pears with conspicuous dead branches or limbs that have a peculiar dark colour and often clinging shrivelled leaves and/or fruit are likely afflicted with fireblight, a systemic bacterial disease. Commercially, antibiotics are used to fight this plague, but with limited and decreasing success. As an organic grower, your first line of defense is to cut and burn the affected parts, again well below the damaged area. Try to make a clean removal at a natural juncture.

Peaches, nectarines, cherries and apricots in age usually have one or more areas from which gum is extruding. This is usually the result of winter damage or mechanical damage such as sloppy pruning. This gummosis can be infected with bacterial canker which might eventually kill the tree. Remove these gummy limbs and twigs, again at a convenient natural juncture.

If the area is on the trunk or a main scaffold limb, you should leave it and try treating it topically. I have had some success excising such an area and keeping lime/sulphur or Bordeaux mixture on it.

At the same time as your first year limb removal, look for root suckers. Some species such as Prunus insititia (e.g. Damson plum) can form regular thickets. Try to locate the main trunk(s) you want to maintain and cut everything else off at the ground. With apples and pears, root suckers usually originate close to the main trunk but in extreme cases it can be difficult to deter-mine which is the grafted variety and which is the rootstock. At any rate, when you do know - it may take a year of fruitfulness to find out - remove all suckers to help the main tree prosper.

 

To Dress or Not to Dress

This is a bit controversial. There is little doubt that trees possess their own immunity and are fully capable of healing wounds effectively. Where cuts are made into dead wood, no dressing is required since this area is already sealed off. In fact, it may be detrimental by sealing unwanted moisture into the wood and inducing rot. Where cuts are few and small, there is no disease and you are moving into a warm period, no dressing is necessary. Where black knot, fireblight or bacterial canker has been removed, paint the cuts with lime/sulphur or Bordeaux mixed with soot from your stove pipes in colder weather. These organically acceptable fungicide/bactericides will have some beneficial influence on the tree’s condition. The soot helps to darken the mixture so as to absorb sunshine and speed healing. Check out commercial dressings before you buy them. Some may contain compounds unacceptable to organic certification agencies. If you do put on wound dressings, use a dark colour to absorb heat in cold periods, when you want to encourage healing and on all large pruning stubs. In warm periods, use white. Always use white on trunk and crotch wounds and on peach trees (which are pruned in warm periods only).

In the fall, after leaf drop, all dressed wounds, crotches and trunks should be painted white with a non-mercury-bearing latex paint or lime-based whitewash. This will guard against bark and cambium damage associated with the freezing and thawing of winter.

 

Maintenance Pruning

All of the principles of timing, dressing and disease management outlined for renovation pruning apply here. The main difference between the two is that relatively larger limbs are often removed in the second year of renovation pruning.

If your tree has a defined shape it is best to adhere to that shape. It will usually have been trained to one of two systems:

• Open Centre (see Fig. 1): This is where the scaffold limbs originate at the trunk and radiate from roughly the same height, much like spokes on a wheel.

• Modified Central Leader (see Fig. 2): In this system the scaffold limbs are staggered up the trunk, each facing a different direction.

Maintenance pruning involves checking your trees annually for these main problems:

1) diseased, dead, broken and overgrown limbs;

2) root and trunk suckers;

3) watersprouts; and

4) poorly positioned fruit spurs and branches.

 

Diseased, Dead, Broken and Overgrown Limbs

Few diseases are serious enough to warrant the chain saw. Remove any dead and broken wood. Occasionally limb or other damage can be repaired. I have successfully tied together an apricot that was split right down the middle and laid flat on the ground in a 52 mm freezing rainstorm, so always consider repair of an important limb. If the whole tree is diseased, try dealing first with its root and trunk suckers to get an idea of its chances for survival.

 

Removal of Root and Trunk Suckers

Rather than proceeding blindly and routinely with this operation, take a good look and consider some options. Trunk-borne watersprouts, if well positioned, can be used to replace a poor or diseased scaffold limb. Don’t cut unless you know for sure you don’t need it. Sometimes leaving a new shoot for a year or two will give you a clearer idea of its potential future role.

Root suckers can be prophets of doom. Some rootstocks produce copious suckers under just about any conditions; when reluctant types continue to push forth, they are trying to tell you that the upper part of the tree has problems and is limiting sap flow for one reason or another. The healthy roots are trying to grow another tree to alleviate the problem. If your tree is on its own roots, training one of these suckers to maturity is a good way to grow a healthy new tree. If it is grafted, you could field graft a new tree onto a root sucker and even change to a more desirable variety in the process. Or you can simply cut them all away and hope for the best.

 

Watersprouts

These are one- or sometimes two-year-old wood that arises from areas of the tree that provide vigorous growth. This includes crotch areas remaining when a limb has been removed, areas closer to the trunk than a diseased area or the higher part of an arched limb. They often occur in clumps and can become fruitful in two or three years. Some are useful in replacing other limbs but usually they can be removed since they drain the tree slightly, provide little food as they are often shaded and cut down air circulation in the centre of the tree. Organic fruit trees need air circulation. Occasionally watersprouts can get so out of hand that they can limit light penetration as well.

 

Poorly Positioned Fruit Spurs and Branches

As part of your renovation and maintenance pruning, limbs that otherwise are healthy and fruitful but are too high and adversely shade other parts of the tree can be removed. This allows lower, more conveniently placed fruit buds to prosper, giving them a better location with respect to light and air circulation.

You will need to determine how spurry your tree is and whether it is a terminal bearer. Tree species and different cultivars vary in their fruit-bearing habit. Apricots and plums are generously endowed with spurs and blossom buds while apples vary. Some are entirely spurry while others are completely terminal in their habit (see Figs. 3 + 4). Spurry trees can be pruned radically to shape and limit growth and still produce lots of bloom, while terminal bearers need most of last year’s growth to produce a good bloom.

Most fruits will do reasonably well unpruned so long as problems 1, 2 and 3 are dealt with, but to increase fruit size and quality some crop limitation and fruit positioning is required. Limiting the crop through pruning also assists in reducing the tendency to bear every other year in those varieties so inclined. Removal of undersized fruit-bearing wood or shaded wood allows the tree to concentrate on the fruit and wood most favorably located. Heavily spurred trees can be trimmed to reduce terminal fruit set. Sometimes supports or stretchers can be employed to position branches for maximum light exposure.

There is a general hierarchy of trees with respect to their training and pruning requirements:

• Peaches and nectarines should be trained to an open centre (OC).

• Sweet cherries should be trained to either OC or modified central leader (MCL).

• Sour cherries should be trained to MCL.

• Apples should be trained to either, with preference to MCL.

• Apricots should be trained to MCL.

• Pears should be trained to MCL.

• Plums should be trained to MCL, with the proviso that the centre of the tree needs more shade than the other species.

There are myriads of shears, saws, secaturs and other pruning tools available. The ones I favor are bypass secaturs, lopping shears and reverse cut (cut on a pull) pruning saws that have a tapered blade (thicker at the tooth than the spine). Whatever you use, keep the blades sharp. Learn how to sharpen them so your cuts will be smooth with less tearing. Poor cuts are much more susceptible to disease and can make good hiding places for insects.

Happy pruning!

 

 

Copyright 1993. Phil Mathewson

Reprinted with permission. All rights reserved.


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