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Garden Life: Refresh your knowledge before pruning

By Robb Rosser

Published: February 19, 2015, 12:00am

Robb Rosser The crew from Distinctive Landscape gets an early start on seasonal hedge trimming at Officers Row.

Late winter or early spring, before buds break from bare tree branches, is the time to prune most deciduous trees and shrubs. This includes fruit, flowering and shade trees. Trees have a unique healing process. Unlike our skin wounds, where skin cells regenerate to heal skin tissue, trees work to “wall off” or compartmentalize their wounds. That process of forming callus tissue forms quickly at this time of year.

As always, I remind you not to prune any spring-blooming plants at this time. Think about it. If you pruned these trees now, you would remove this year’s flowers. If you’re not sure when your plants flower, find the plant tag and look up the exact name in a reference book or take a sample of the plant with stems and buds intact and ask a professional at one of your favorite garden centers.

Spring-blooming plants flower on wood that formed last year. Prune these only after they have finished flowering. A prime example in Washington is the rhododendron. Only after the plant has finished blooming would you deadhead, or snap off the spent flower heads. This kind of pruning encourages next year’s bloom. You can also reach into the shrub and cut out crossing or overly long branches to enhance the natural shape of the plant. Some other spring bloomers are azaleas, forsythia, mockorange and flowering quince.

Sometimes, all the different rules and gardening concepts get as tangled up as the plants that we need to trim. It’s no wonder the suggestion of pruning causes many gardeners to shudder with apprehension. I find that the key to understanding how to prune is to answer the question, “What is the purpose for pruning this particular plant?” Remember, every plant does not need to be pruned. In my opinion, most plants look best if allowed to follow their natural form.

The general purpose of pruning is not to reduce the size of a plant that has grown too large. Pruning stimulates growth. Weak growth can be stimulated by cutting back significantly and vigorous growth is best checked by light pruning. This is important to know if you are fighting to keep a large shrub within the boundaries of a small space. The best pruning advice for a plant that is too large for its location is to move it.

Most pruning is done only once a year. Thinning certain shrubs, which is just another form of pruning, is done only every two or three years. The most effective reasons for pruning are to help establish the shape of a plant along its natural lines; to improve flower or fruit production; to control the time of bloom (as in pinching back chrysanthemums); and for espalier and hedge shaping. These are all methods of seasonal pruning that enhance a plant’s best qualities

Plants that can be pruned from late winter into spring are plants that will bloom later this summer on wood produced this growing season. These include abelia, Rose of Sharon (Hibiscus syriacus), butterfly bush (Buddleia davidii), caryopteris, hypericum, shrub roses, and Russian sage (Perovskia spp.). For these plants, hard pruning produces a well-shaped shrub that flowers vigorously in late summer or fall.

Prune shrubs grown for colored winter stems before new spring growth begins. These include the shrubby dogwoods (cornus alba and cornus stolonifera), the bright salmon red salix britzensis and the ghostly, white-stemmed bramble rubus cockburnianus. The key to successful pruning of all of these shrubs is to keep them eternally young; vigorous new shoots are longer and more brightly colored or bloom more freely than older, unpruned growths.

It’s only natural to need to refresh your memory before tackling a job that you do infrequently. Make it part of your pruning habit before each outing and only deal with the type of pruning needed in the current season. If you have a large yard with a variety of trees and shrubs, or are particularly interested in the art of pruning, I highly recommend that you buy a basic pruning book to keep on hand.

I continue to recommend the book, “Pruning and Training Plants” by David Joyce and Christopher Brickell. The American Horticultural Society and the Royal Horticultural Society have both published new editions of this book with the same content. One complete book is all most gardeners will ever need, as it thoroughly covers each type of plant, as well as groups of plants. Without a doubt, having diagrams and photographs to look at before you tackle each type of pruning job will improve both your confidence and competence.

Robb Rosser is a WSU-certified master gardener. Reach him at Write2Robb@aol.com

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