NDSU Extension - Burke County


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Pruning Trees

County Agent News
Dan Folske
April 9, 2018 

Pruning Trees

          When should I prune my trees and why should I prune my trees are two common questions I get from this time of year through late June.

          The first question, “Why?”, can have a lot of different answers. Modifying the appearance and preventing or treating disease are the two main reasons. Homeowners can have many different reasons for modifying appearance. It may be minor trimming to maintain a neater appearance. Unfortunately it is often to remedy a problem which started many years before. The wrong tree or shrub in the wrong place. Species and variety selection are the most common landscaping mistakes made by homeowners. Planting location is also part of this problem. Species and varieties with mature sizes which are too large for the planting location can be a costly mistake. Most tree and shrub species can be kept trim and neat if pruned regularly but all too often the pruning doesn’t get done and a homeowner ends up hiring a tree removal/ pruning service to remove large trees or limbs that have become a threat to power lines, roofs, siding and other parts of the property. Roots of trees planted in the wrong place can also become a threat to sewer lines and building foundations. Smaller trees and shrubs can also become too large for their locations. Most shrubs like Lilacs and Caragana can be cut back either small amounts or all the way down to just above the soil line. These shrubs will regrow to a nice moderate size within a few years. Cedar, Juniper, and Arborvitae however will not get new buds and growth from old wood. Sever trimming or topping of these species can leave a very unsightly shrub or tree which will take many years to achieve a more normal appearance and may not ever do so.

            The second part of the “Why” is disease prevention or treatment. Opening up the canopy of apple or other fruit trees allows freer movement of air throughout the canopy which speeds up drying of the canopy after a heavy dew or a rain event. This makes the tree much less susceptible to diseases of the leaves, branches, or fruits. It also makes applications of fungicides, insecticides or insecticidal soaps much easier and more effective when needed. Trimming of infected branches is an important part of treating diseases like fireblight.

            Pruning of apple and other fruit trees also lessens the fruit load of the tree allowing the tree to put more energy into a healthy root system and into development of next year’s buds. This may lessen this year’s crop but will provide a more consistent crop from year to year.

            The other big question is “When”. That depends on both the species and the “Why”. Generally late fall or very early spring are good times to prune. Spring pruning of most species should be done before the buds start to swell. Waiting until after buds swell and trees begin to leaf out can weaken the tree and also leaves an open wound for disease pathogens which are active in warm wet weather.  Late spring pruning of most species after they have broken dormancy will result in a great deal of weeping from the wounds which is both unsightly and a veritable “free lunch” sign to insects which can be disease vectors. For ornamental crab apple species and lilacs I like to wait until after bloom for major pruning. These species will develop next year’s flower buds on this year’s growth so pruning after flowering allows regrowth and the setting of buds for next year’s flowers.



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