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Primer on Pruning

January 9, 2012
Julie Monson

As an observer of gardens everywhere, I’ve become particularly sensitive to how trees and large shrubs are pruned.  While not all mature trees require pruning, many are healthier and more attractive when sensitively pruned. I find it’s always a pleasure to admire properly pruned, mature trees in public and private gardens. Often, however, one sees in the urban landscape perfectly dreadful examples of trees tortured by heavy-handed, unorganized chopping, and shrubs rounded by power hedge trimmers into unnatural green balls.  It doesn’t have to be that way.

The subject of tree and shrub pruning is far too vast to cover in this article.  I can begin, however, with some basic concepts followed by examples from my own garden.  For many plants, pruning is best done in winter (January and February), when plants are dormant, resting up for their spring growth.  Now is a good time to examine your garden and make a plan for any necessary pruning in the coming months.

Pruning is cutting back or cutting off branches of any size in order to shape a tree or shrub.  Judicious pruning can help train young plants, tidy up a plant’s appearance, control shape and size, promote flowering and fruiting, invigorate stagnant growth, and remove damaged or pest-infested growth.  If properly shaped when young, most trees and many large shrubs require little pruning after they mature. 

The two main types of pruning cuts are heading and thinning.  Heading is cutting from the tip back to a lateral branch, and I imagine heading as a haircut, since it is often done uniformly over the plant.  Typically, plants respond to heading by producing new shoots directly below the cut.  Heading is not a useful technique for reducing the size of a tree or shrub for the plant will respond by producing more growth at its tip or top. 

Thinning involves removing a branch back to its origin, or shortening a branch’s length by cutting to a lateral large enough to assume the terminal role.  Thinning is preferred if the object is to retain the plant’s natural character.  Properly done, thinning opens up the center of the plant and removes crisscrossing or other branches that interfere with its natural shape.  Thinning also requires the pruner to make many decisions about which branches to remove. This can be unnerving for the novice home gardener and takes some practice.  Most “mow and blow” gardeners have not been trained to thin trees properly, which is why you often see heading rather than thinning on plant material in shopping centers, public and private gardens. Professional, trained arborists practice thinning, especially (in my experience) when asked to do so. 

Around the first of January, I start my annual inspection of all the shrubs and trees in my Japanese-style garden, with an eye to which might need pruning and how much.  The azaleas will need heading, that is, shaping into curved forms, but not until they have bloomed. If I did it in January, I would cut off all of March’s flowers.   Nandina is pruned by cutting older stems at ground level and by removing sprays of spent berries.  I will shear the ground cover, Blue Star Creeper. 

Maples are my biggest challenge.  Last winter, I decided to raise and open the leafy maple tree canopy in order to allow more sunlight into the garden.  This was a task far beyond my tools, expertise and strength.  I hired an aesthetic pruner and he did a fabulous job, following the basic tenants of thinning.  Ordinarily, mature maples do not require pruning, but in this case I felt that the garden would be much improved with more sun for understory shrubs and groundcovers.   Evergreen shrubs, such as choisya, huckleberry, camellia and correa, I will prune with thinning techniques to improve their shapes.  I will enhance my pots of bamboo by cutting off the older or dead canes.   My point here is that one size does not fit all.  Each plant has its own needs and genetic direction.  My job is to help that plant thrive given its natural inclination. 

My plant inspection is followed by a tool inspection.  It’s time to take my clippers, loppers and saws down to the hardware store to be sharpened.  Sharp, well-oiled, clean tools make pruning much easier. 

There is much more to pruning. Other useful sources of information include:  Sunset Western Garden Book and The American Horticultural Society’s Pruning and Training: A Fully Illustrated Plant-by-Plant Manual by Christopher Brickell and David Joyce.

Sometime in the next few weeks, I will have my annual conversation with my garden plants and work out our winter pruning plan.  It’s a very nice way to spend a winter’s day in the garden.

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