Why Do We Prune?

Why do we prune in gardens and in the Preserve?  Some reasons are obvious.  Diseased or damaged branches need to be removed as soon as possible to prevent the spread of disease.  Growth that presents a safety hazard must also be removed promptly.    But we prune plants for reasons other than safety and health.

One reason is to shape them.   If growing a hedge, we prune out  irregular branches in the beginning and then maintain the shape by regular hedge-trimming.   Similarly, we remove branches that grow in the wrong direction when training a new tree to a pleasant shape.   Some local gardeners take plant shaping to a high level, creating elaborately shaped shrubs in traditional Japanese or European styles.   These examples demonstrate the degree to which certain plants can be shaped.

Gardeners sometimes prune to control the size of trees and shrubs, often with limited success.  In general, plants continue to grow until they achieve their natural mature size.  They will keep trying to achieve this size – or die in the process. That’s why pruning to limit size is an endless task.  It’s far easier to choose a plant with the right natural size in the first place.  This is particularly important with California native shrubs, some of which become quite large.   But choosing a plant based on its mature size makes sense for any plant. 

Southern California’s native trees, shrubs and even grasses need to be pruned for another reason – to keep them youthful and healthy.   Hikers sometimes comment that wild shrubs appear to be pruned by an expert gardener.  In a way they are, but the ‘gardener’ is not who you might expect.

In truly wild areas, deer, rabbits, elk  - even wildfires, wind and water - prune plants on a regular basis.   Deer and elk browse the fresh growth of trees and shrubs in spring and summer.  Rabbits eat grasses and smaller vegetation.    The plants respond by producing new growth.  If the plant is not over-grazed, the result is a plant that’s fuller, more youthful and more attractive to the eye.

Fires also play a role in plant regeneration.  In the past, wildfires burned local foothills and mountains every 50 to 150 years depending on the area.  Fires are a consequence of our long dry summers and Santa Ana winds.  This weather pattern also occurs in other mediterranean climates like the Mediterranean region, South Africa, western Chile and western Australia.  

Plants from mediterranean climates have adapted to fires over the course of thousands of years.   Many mediterranean climate trees and shrubs have the capacity to re-grow after fires, allowing them not only to survive but also to rejuvenate themselves.    In fact, these plants are so dependent on fire that they literally need periodic fires to survive.   Without them – or their surrogate in the garden - they die prematurely.

Native Californians understood the need for periodic rejuvenation.  In the past, they regularly pruned, divided and even burned plants to keep them young and productive.  Over time, Native Californians became an integral part of the natural cycles of plant life.  They literally became a force of nature.

Most gardens and smaller nature preserves are no longer home to deer, rabbits and other forces of nature.  Even the wind patterns and water flow are altered in populated areas.   But the native plants still need the yearly and occasional catastrophic processes that keep them youthful and healthy.  And that’s where proper pruning plays a role.

Like the deer and rabbits, we need to prune back some of the fresh growth on native shrubs to encourage dense, well-shaped plants.   Like the wind, we need to prune out weak and damaged growth.   And like fire, we occasionally need to prune mature native grasses and some shrubs more harshly.   We literally ‘become’ the deer, rabbits, wind and fire for the native plants in our care.

Pruning native plants is not difficult, but you do need to know how to prune each plant.   Prune a native plant incorrectly – or at the wrong time of year – and you risk damaging or killing it.   The trick is to imitate the natural processes.  Many of us have little direct experience with these processes in the wild.  That means we need to learn how to prune our native plants. 

One easy way is to attend a pruning workshop at Mother Nature’s Backyard or the Gardena Willows Wetland Preserve.   The fall/winter pruning season is almost over, but we will have sessions in summer and again next fall.  See our schedule at http://www.gardenawillows.org/events.htm,   or call 310-217-0681.  Pruning classes are also given at CSU Dominguez Hills (see http://nativeplantscsudh.blogspot.com/p/calendar.html). 

For more information on pruning common California native plants see http://nativeplantscsudh.blogspot.com/2012/11/pruning-common-native-plants.html  or http://mother-natures-backyard.blogspot.com/2012/11/pruning-common-native-plants.html    A great book which includes information on pruning is California Native Plants for the Garden by Carol Bornstein, David Fross & Bart O’Brien (Cachuma Press, 2005). 

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Constance M. Vadheim  (Adj. Professor of Biology – CSU Dominguez Hills; Board Member – Friends of Gardena Willows Wetland Preserve)