Large, unpruned apple trees can be bucolic in the landscape, but they are not particularly productive. The longer a tree have been unmanaged, the harder it is to rescue. However, sometimes a neglected tree is present when purchasing or inheriting property. Also, owners may have an emotional connection with a particular apple tree and may want to preserve it. Although it usually takes multiple years to restore an overgrown tree, it may be worthwhile if it isn't heavily infected with disease or infested with insects.
In the case of an abandoned apple tree or orchard, it is often easier to replant with improved cultivars, especially those infected with fire blight. Newly-planted trees on dwarfing rootstocks require only three growing seasons to begin cropping. Alternatively, trees can be cut off and their limbs top-grafted with a desirable cultivar (see University of Missouri Extension grafting publication at: https://extension.missouri.edu/publications/g6971), but this requires some level of skill. Another approach is to purchase a rootstock and use scion wood collected from the old tree to propagate a new one by grafting. However, it is sometimes difficult to purchase only a few rootstocks from suppliers.
To determine whether or not to rejuvenate an apple tree by pruning, begin by assessing its canopy. A mature tree that has not been carefully maintained will have a round-shaped canopy or will be wider at the top than at the bottom. It will also bear few apples in the lower two-thirds of the canopy. A tree in this overgrown condition will require at least three years of intensive pruning and moderate annual pruning thereafter.
Dormant pruning, usually in February or early March, is used to rejuvenate an overgrown apple tree. In the first year, try to re-establish a center leader. Begin to lower the height of the central leader and reshape the tree into a pyramidal form. Then open up the canopy to allow better sunlight penetration into the tree interior and allow better air flow. Remove no more than six big limbs at the main trunk. Select branches for removal that are broken, diseased, or lie directly over another and shade the lower limb. Also, main limbs growing at narrow angles (less than 45 degrees from the central leader) are easily broken when fruit is present and should be eliminated. When making pruning cuts, cut main limbs back to the trunk. Take caution to remove no more than one-third of the tree canopy in a year.
In following dormant period, it may be necessary to remove a few more large-diameter limbs, especially in the upper portion of the canopy, to attain a pyramidal tree form. Also, there will be a flush of growth originating from the pruning cuts made in the previous year. If a renewal shoot is needed in that part of the tree, leave one new, outward-growing shoot that has a wide angle from the trunk and remove other shoots from the older cut. Continue thinning out smaller-diameter branches by cutting back to the main limb rather than making cuts between internodes. Eliminate branches that cross each other or grow towards the center of the tree or in a downward direction. Continue to reshape the tree canopy into a narrow pyramidal form and open it up to allow light into the tree for good fruit bud development throughout the tree.
By year three, the desired structure of the tree may be re-established and fruit will develop on the lower limbs. Continue removing any upright sucker growth and extra shoots arising from last year's cuts, leaving a shoot for renewal growth if needed. When pruning, always remove wood at a major juncture of two shoots, limbs, or a limb and the trunk to avoid stimulation excessive new growth.
In subsequent years, prune annually during the dormant period to stimulate small-diameter fruiting wood. In all years, remove any diseased limbs. If fire-blight infection occurs (necrotic, die-back at shoot terminals), prune the shoot at least six inches below the symptomatic tissue) as soon as it appears in the spring and summer. When removing fire blight-infected tissue, dip pruning shears in a disinfectant, such as 70% isopropyl alcohol, between each cut.
When rejuvenating an apple tree, have patience. It takes several years to reverse the effect of multiple years of neglect.
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REVISED: January 7, 2021