Thursday, May 12, 2016

PRUNING by Sharon Faircloth

Admit it, you’re either intimidated by pruning or you attack with a relish!  I fall into the scaredy cat variety.  It seems so overwhelming to know when to do it, if you should do it and what if you don’t do it right.  Luckily, if you need some courage or a refresher, there’s very detailed information from CSU Garden Notes and our Extension Offices to assist.

So firstly, why is pruning important?  With deciduous trees, it’s necessary to develop structure in young trees and maintain structure in mature trees.  Living in the high country where we have mostly evergreens, little pruning is needed.  Helpful hints on pruning evergreens can be found in CMG Garden Note #617.  It’s also helpful to know how to remove limbs causing a hazard or for safety.  Good idea to hire professionals if your trees need to be cleared from electrical lines!

When pruning evergreens, protect against damage to the trunk.  Pruning the trunk leaves the tree susceptible to smaller leaders developing and then the tree may be damaged by wind and the elements.  To ensure structural integrity, make sure all the branches are no more than one-half the diameter of the trunk. There is extensive information on pruning cuts in CMG Garden Notes #612.
On evergreen trees, remove large branches back to the trunk using a three-cut method.  Make the final cut just outside the branch collar.  Needles only grow from the growing tips out and will not develop on the interior branch wood without needles. CMG GardenNotes #617 online at

So when is the best timing to prune?  If you have hazards, dead or diseased limbs, you can prune anytime of the year.  With live branches, it gets trickier.   If you do want to prune or shape young evergreens, it’s best to do it late winter or early spring.   The firs and spruce are tolerant to pruning but slow-growing species are best left alone. 
Pruning spruce and fir back to a side bud or side branch will encourage growth of side branches. [Line drawing by CSU Extension]  CMG Garden Notes #617 online at
Rather than pruning young pines, it’s preferable to pinch back the new growth tips rather than risk damaging terminal buds. 
On pines, for bushier new growth “pinch” growing tips by snapping off one-third of the “candle” tips with the fingers.  Because pines produce few side buds, they are intolerant of more extensive pruning. CMG Garden Notes #617 online at
Pruning junipers and arborvitae back to a side shoot hides the pruning cut. [Line drawing by CSU Extension] CMG Garden Notes #617 online at
Pruning junipers and arborvitae rarely needs to be done but the best time is spring and the best method is cutting individual branches.  Growth comes from the tips so if you cut back to the trunk, it will not grow back.  Shearing is rarely recommended and one easy tip to remember is NEVER prune during drought!

More common pruning used in the higher altitudes is for flowering shrubs.  Pruning will help shaping, protection from pests and enhance flowering.  Thinning, done in the spring, will encourage new growth. A guideline is to remove one-third of the oldest wood to the ground each year.

Rejuvenation pruning is when you take a shrub back to the ground early, before any growth.  New growth will come from the roots and then it will start back like a new plant.  Usually this method is done every 3-5 years and works best on more woody shrubs like potentilla and blue mist spirea.  The down side is that the shrub will not bloom that year and if it’s too woody or has too many dead branches, it probably won’t respond as well.

Shrubs that flower in the spring like spireas, viburnums, lilacs and forsythia develop buds midsummer through fall.  Rejuvenation should be done in early spring and thinning after the blooms have dropped.

Butterfly bush, Rose of Sharon, and other summer blooming shrubs do better if you remove older canes allowing more sunshine and encouraging flowers throughout the bush.  For more information on how to shape shrubs, please see CMG Garden Notes #616.

Pruning can protect bushes like lilac from oystershell scale and borer problems.  The more air circulation, the less likelihood of various diseases including leaf spot and powdery mildew.

When choosing pruning shears, the anvil-type have a sharp blade and a fixed, non-cutting surface (hence the anvil).  These shears are good for smaller woody stems and work best when kept sharp.  It’s preferable to have an ergonomic design and quality parts.  You may also want to make sure you can tighten or loosen so that it cuts with precision.  The head size will correlate to the diameter of the branch.

So to my scaredy cat friends, go forth and clean up your shrubs and easy does it to you enthusiastic hackers!

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