overgrown apple tree tops

Apr 6, 2022
Tips for managing tree height, apical dominance in apple orchards

Managing tree height in orchards can be a difficult task. Michigan State University Extension shares concepts and practices to help maintain apical dominance and tree shape.

Once trees fill the canopy space and reach the top wire, they may become too tall, shading out nearby trees in the orchard, or they may have many laterals competing with the central leader (pictured at top). Cutting trees back excessively or using heading cuts can lead to a vigorous flush of growth at the top that is difficult to manage. In general, heading cuts result in overly dense canopies, as compared with thinning cuts (Figure 2).

Heading cuts remove apical dominance
Figure 2. The result of heading cuts (left) compared to thinning cuts (right) after a couple seasons of growth. Heading cuts remove apical dominance, causing lateral buds to break, the production of many vigorous shoots, and an overly dense canopy. Source: MSU Extension

Understanding apical dominance and related pruning concepts can help inform strategies for managing tree height. Apical dominance is the concept that the apical or terminal bud exerts control over nearby buds. A plant hormone produced in the apical bud, called auxin, is transported basipetally, or downward. This suppresses nearby (lateral) buds, preventing them from breaking. However, if the apical bud and the auxin produced in it are removed, buds directly below will break.

removal of competing laterals in apple trees
Figure 3. Selecting a single vertical shoot and removing competing laterals. Before (left) and after (right). Photos: Ron Perry, MSU

Strategic pruning cuts can be used to mitigate this concern. Before trees reach their full height or become overgrown, tops should be managed by selecting a strong apical shoot and removing any competing laterals during dormant pruning (Figure 3). This will maintain the central leader growing habit of the tree and keep the top narrow to prevent shading of the lower part of the canopy.

pruning weak lateral top in apple tree
Figure 3. Once a tree reaches its full height, it should be maintained by cutting back to a weaker upright shoot. Photo: Todd Einhorn, MSU

If tops become overgrown, the height may need to be reduced using bigger cuts. The result can be a big flush of vigorous upright shoots. One strategy that can be used to maintain apical dominance is to cut back to weak lateral growth (Figure 4). Sometimes this is not possible because trees are too tall or there are no good alternate shoots available. In this case, apical dominance can be maintained by replacing the natural auxins in a tree with a synthetic auxin application. NAA (1%) can be painted onto the tops where pruning cuts were made. This should be done 1) following a summer heading cut to prevent regrowth or 2) following a dormant cut, but only once the sap begins to flow in the spring (bud break). A summer pruning cut may be preferable in this case because the response will be less vigorous than a dormant pruning cut. However, there is often more time available during dormant pruning, and cuts may be easier to see.

– Anna Wallis, Michigan State University Extension


Current Issue

On-farm AI: Water, farm, labor research guide decisions

Data collection tool expands farm management

Carmel Valley winegrapes: Parsonage Village Vineyard

IFTA Yakima Valley tour provides orchard insights

IFTA recognizes tree fruit honorees

Pennsylvania recognizes fruit industry professionals

Fresh Views 40 Under 40

see all current issue »

Be sure to check out our other specialty agriculture brands

produceprocessingsm Organic Grower