By Sarah Christian

WHY PRUNE?
If a plant is planted in the right place, minimal pruning will be required. People often don’t do their research on a plant’s mature size and plant it in a space that is not big enough. Windows may become covered or paths or gates may become obstructed by growth. Furthermore, plants can be placed too close together by those in search of instant gratification and a full look. A few years later, the plants have to either be drastically pruned or removed. Over time, excessive pruning weakens and disfigures shrubs and results in a lot of unnecessary work and yard waste. However, If you have selected a plant whose mature size fits its location, there are several reasons when pruning is appropriate.

1) Health – prune dead, damaged or diseased wood so that energy can go to producing new growth
2) Crossing branches that rub together – one of the two should be removed
3) Undesirable growth – suckers at the base of a plant, limbs encroaching on sidewalks, etc.
4) To encourage flowering – by thinning at the base or rejuvenation. Proper methods of pruning to encourage flowering will be discussed below.





HOW TO PRUNE

“A good pruning job is like a good haircut. It should hardly be noticed at all.”





 PRUNING TYPES

Many shrubs will look their best when allowed to grow to their natural form with just occasional pruning of dead, damaged or diseased wood. Avoid making cuts at a uniform edge creating a round ball or other unnatural shape or across the top of a shrub. This is a common pruning technique because it is quick and easy.






Frequent, unnecessary shearing that is done incorrectly can cause shrubs to lose their natural shape, resulting in an unhealthy structure with dead sections and reduced flowering.





If you really want a tightly sheared look in your garden, choose a plant that is suited to this type of pruning such as boxwood.


1) Branch by Branch Shaping

One proper pruning technique is branch by branch shaping which involves cutting the longest and oldest branches back to the point of origin where the branch grew from its parent branch.. This results in branches of varying lengths and a more natural looking shrub. It is an acceptable method for deciduous shrubs but does not significantly encourage new growth of wood on flowering shrubs for maximum bloom.


 2) Thinning

One of two methods to encourage shrub flowering is thinning. The objective is to cut one-third of the oldest wood to the ground each year which stimulates new, better flowering growth from the base of the shrub. This method is time-consuming and does not work well on twiggy, multi-stem shrubs like spirea. For overgrown shrubs, it is best to do rejuvenation pruning, followed by thinning.



 3) Rejuvenation

The other method to encourage shrub flowering is rejuvenation. Rather than just cutting one-third of the oldest wood, the shrub is cut entirely to the ground or just above it in the early spring before new growth starts. The shrub regrows from the roots, giving a compact new plant with maximum bloom. This method is preferred for many flowering shrubs such as multi-stemmed, twiggy-type shrubs such as Spirea, Blue Mist Spirea, Potentilla, Red-twig Dogwood, Sumac, and Hydrangea. You can also use this method to rejuvenate Lilac, Privets, Barberry, Forsythia, Quince, Mockorange, Weigela, and many Viburnums. Rejuvenation should be followed by thinning new canes to several strong ones over the next several years with weak cane growth removed at the base. After three to five years, rejuvenation may be repeated again when the shrub begins to look woody.



WHEN TO PRUNE

If pruning is necessary, you can do light, corrective pruning any time of the year. More severe pruning of most deciduous trees and non-blooming shrubs should be done during their dormancy in the late winter to early spring before they leaf out. Insects and disease spores are less likely to infest pruning cuts during this time. This is especially important for fruit trees that are vulnerable to fireblight. It is also easier to see the plant’s form when it is without leaves. In spring to early summer, energy reserves are being used for new growth and heavy pruning can weaken a tree or shrub. By late summer and early fall, plants begin storing their energy reserves in their roots to use in dormancy for next season’s spring growth. Pruning should be limited during this time since it may encourage new growth that would not have time to mature before being subjected to freezing temperatures. By late fall after they have lost their leaves and there have been several hard freezes, more of the energy reserves are in their roots and there is less stress on the plant.

Exceptions:

Spring-flowering shrubs bloom on the previous year’s growth. Flower buds develop in midsummer through fall so pruning in the fall and winter removes the coming year’s flower buds. If you thin right after bloom before the flower buds are set you will maximize the next season’s flowers 


Spring-flowering shrubs include Forsythia, Nanking Cherry, Quince, Bridalwreath and Vanhoutte Spireas, Viburnums, Beautybush, Lilac, Peashrub and Weigela. It is recommended that you deadhead the faded flowers after they bloom. This not only makes the plant look tidier but conserves its energy for seed development.

Summer-flowering shrubs bloom on new wood that grew earlier in the current growing season. Flower buds develop in midspring through midsummer so pruning during this period removes the season’s flower buds. If you thin right after bloom before the flower buds are set you will maximize the next season’s flowers. Removing older canes of flowering shrubs also allows better sunlight penetration which results in better flowering throughout the shrub instead of just at the top.


Summer-flowering shrubs include most Butterfly Bush, Blue Mist Spirea, Hancock Coralberry, Mockorange, Potentilla, Japanese Spirea, Annabelle and Peegee Hydrangea, and Althea/ Rose of Sharon.

PRUNING TECHNIQUES FOR TREES & SHRUBS

Know where to cut: A very common pruning mistake when removing branches is to cut them off too close to the main trunk. By doing this, you remove the branch collar, an area of tissue cells that help the pruning wound to heal. The branch collar looks like a small swelling or bump and is located where the branch meets the trunk. This natural protection boundary prevents disease from entering the trunk. Without it, you open a wound that allows entry for disease and pests. The rules are don’t cut branches flush to the trunk, don’t leave stubs, and cut at an about a forty-five degree angle away from the tree or shrub as shown in the drawing and photo below.




Know How to Cut: When pruning trees, heavy branches can fall and rip bark before you’re done making a clean cut. To avoid this, use a three cut method as described below. If you feel like you are in over your head, contact a certified arborist.



Over-pruning: Trees should not be pruned until about five years after planting other than removal of dead or diseased limbs. No more than about 25% of a mature tree's limbs should ever be trimmed off per season. If a tree is already stressed, it should not be heavily pruned or it will be unable to produce enough food and transfer nutrients.

About Urban Gardens, Inc.: Urban Gardens provides landscape design and consulting services to residential clients whose projects range from historic renovations to new subdivisions with a blank slate. Sarah Christian owns and operates Urban Gardens in the internationally recognized Stapleton Development in Denver, Colorado. She received her Masters degree in Landscape Architecture from the University of Colorado at Denver in 1995 and has worked in Colorado since that time. She is licensed by the state of Colorado and is a member of the American Society of Landscape Architects. You can visit her web page at www.urbangardensinc.com