|The best time to prune your evergreen trees and shrubs comes at my favorite time of year; just before they begin to grow. This is called dormant season pruning and is generally done between February and May. Both seasonal factors and species will influence your pruning decisions. Is your plant in the appropriate environment? If not, you may have to contort your shrub into something it would rather not become. So often we prune as a result of site limitations or other environmental factors that were not considered during the design / installation phases. The use of natives and plants that work, along with wise placement is critical in the development of a successful design. Environmental requirements are more important to a plant’s survivability than are those of aesthetics. Therefore site selection is critical. So, once plants are in, what’s next?
Topiary gardens certainly have their place, but transforming the Plant Kingdom into the Animal Kingdom is stressful on a plant’s physiology. (Remember, pruning is a matter of tangible, genetic relationships not magic). Leaves generally cannot grow without a relationship with light. Sunlight, for which they hunger, is all-powerful. Shearing evergreens forces them to grow leaves along their outer parameter only. This inhibits light from reaching the plant’s interior and debilitates the tree’s ability to manufacture or work with chlorophyll. The phenomenon of photosynthesis is the keystone to plant health, and we can make sunlight available to the entire evergreen through a technique called naturalized pruning.
In contrast to shearing, which cuts off only branch tips creating an even denser shrub, natural pruning reaches into the plant and prunes from within, opening the ends and the interiors to light. You actually want your work to have a transparent or translucent look when viewed from the top or side of the plant. You can still have a formal look or shape but the plant must be open to light if it going to grow leaves along its interior.
Rule #1; take the greatest amount of wood with the fewest number of cuts. If you have two branches that are doing the job of one, remove the weaker of the two. The idea is to see into the plant while helping it look as natural as possible. Plants that respond well to this type of pruning are most hollies such as Nellie Stevens, Japanese varieties, blue holly and Helleri, yews, junipers, boxwood, (especially English box) only to name a few. By opening the plant, it begins to grow leaves on all its surfaces. Simply put, the more open the plant, the more leaves it can grow. The more leaves it has, the more efficiently the plant can feed itself. That’s right, feed ITSELF; we have nothing to do with feeding plants, you cannot feed your plants. We can put things into soil that a plant may or may not use, but as far as the feeding goes, well, we better leave that to the Almighty or Pan and their ole buddy the sun! (I guess that was kind of a smart allec lecture and I apologize, but the facts are what they are). The evergreens we prune every year or every other year are the one’s we rarely treat for mites, insects or diseases and most species of evergreens can be pruned this way. On the other hand, large, needled trees are the general exception to the rules, please keep reading.
While hollies and others mentioned are pruned in late winter early spring, there is a group of evergreens that we must not prune during the dormant season. Some are Rhododendron, mountain laurel, azaleas, pieris Japonica or Andromeda and of course Southern magnolia which most people prune after enjoying their late season flowers. Generally, the evergreens that flower with great show and vigor are pruned after the flower show is over and flowers have fallen. They will create their flower buds within the next month or so, but what about those large needled evergreen trees?
Needled evergreens are similar in some ways but are also different from their broadleaf relatives. Placement of spruce, fir, pines is critical. Quite simply they were not made to prune. They grow in a very distinct, genetic pattern and enjoy being in the open with “room to grow”, and when allowed to do so are magnificent. There are, on the other hand a few evergreens that do withstand good pruning and unlike spruce and a few others, will put on new growth as a response to pruning.
Cryptomeria, Leyland cypress, chamacyparis and white pine prune very well. The first three conifers can be pruned the same way most deciduous trees are done. They can be thinned or reduced in size, always remembering to cut back to healthy laterals and “branch collars”. They will begin to fill back in nicely during the next growing season. We will discuss more of that at a later date. White pines respond to pruning in a special way and should be done as one of your final early spring pruning responsibilities. This type of reduction pruning will keep your pines fuller and more compact and it should be done in April.
After weeks of warmer weather, you will begin to notice the “terminal” buds on your white pine are beginning to swell and elongate. They are not yet needles but instead look like a stalk or “candle” protruding from the end of each branch. Stand by. When the candle is at full length, 2-5 inches, it will begin to open, exposing the new tender needles. At this time or just prior, cut one-half to two-thirds off of each candle. That’s right, just cut back the candle. This will disrupt the energy being moved to the end of the branch and in turn re-direct that energy to the side or lateral branches. This is a good way to keep a row of white pines as a hedge, but on the other hand is extremely labor intensive. If we need a hedge, let’s plant a tree or shrub that will grow to your desired height. Remember, it is easier and healthier to choose the correct species for the task, than to ask a large plant to stay small.
I hope that gives you a place to start. There is one more thing to remember. Evergreens are both elegant and functional. Think about that beautiful Nellie Stevens holly hedge that affectionately and laboriously surrounds and protects your backyard; and while you’re picturing that, think about the goldfinches, kinglets and pine siskins that are able to tolerate our winters because they have evergreen trees for food and protection from the elements.
As we care for these shrubs, think of them not only as a weekend task but also as a canvas and your pruners as your brush. Shrubs truly are a work of art and will become more beautiful with age if we will let them.
I’ll leave you with this: The only reason you ever need to prune a large evergreen tree is because it was put where it cannot fulfill its genetic obligation. Once you shorten a fir or spruce or cedar or cypress you begin the long term process of removing that particular tree. Right plant, right place; nothing in the horticultural world is more important. Happy evergreening!! Peter
Copyright 2005 by Peter Deahl. All rights reserved.
The Pruning School 16 Berkeley Court Sterling, Virginia 20165