A GROWING CONCERN: To thin or to head? That is the question

THE GREAT, WARM, unseasonably nice weather continues, so now your pruning must really begin in earnest.

So, again today we will continue our pruning course, keeping in mind the essential tenets:

• Be confident that you can do this correctly and that it is good for the plant.

• Be able to visualize the finished product before pruning down the plant to it’s inner self.

• Be decisive, making each cut for a particular reason in altering the height, shape, size or character of the plant.

With these tenets, let’s add the two basic techniques of all pruning you will be performing.

Regardless of the plant, you will be using a repertoire of two basic cuts: Heading and thinning.


Thinning is a prune designed to remove a branch from which it is originated.

This cut is made nearly flush with the main branch (or trunk), leaving a very small branch collar an inch or less from the main branch.

Never leave a large noticeable stub here to rot away into the plant.

Leaving this small collar helps the plant in callusing over the cut and does not destroy the cambium layer (layer of rapidly dividing living cells that form wood and bark level) crucial to the plant’s survival.

Thinning allows remaining branches to grow naturally in the intended direction and in their normal character.

Thinning opens up the plant, which reduces wind damage, snow load, or ice and rain damage.

Thinning also greatly increases sunlight to both the interior of the plant and the ground.

This increased sunlight creates a healthier, lusher plant and at the same time provides for better growing conditions under the plant.


Heading is the other technique of pruning in which one cuts the branch back to a bud, pair of buds or a node rather then down to the next branch.

When a plant is headed back a lot of the newest tip growth is removed.

Heading tends to remove the terminal (growth tip) buds. This is good, for it causes those bud areas behind the cut to grow (break).

As the nodes break along the branch the plant becomes dense.

When we shear hedges, we perform a type of heading. All those neat topiary plants in various shapes are accomplished by heading.

All too often people head their plants when they should be thinning instead.

The topping (heading) of large trees for views or because of electrical wires is often extreme and wrong.

Thinning is the form of pruning you should use in order to reduce trees, roses, heather, lilacs, evergreen trees or anything into the house.

Heading produces a thick veneer growth right on the surface, which grows faster toward the object upon which it intrudes.

Successive wrong pruning creates a tangled mess of sticks and twigs just underneath the growth line.

In the case of heather or low laying evergreens next to walks and driveways, once you head this inner woody zone, you are left with an unattractive, leafless, brown mob for years to come.

Thinning is the technique to be used, reaching far into the plant and cutting whole branches off the trunk.

This week’s work

So now comes this week’s work. We are off to thin.

First go to any hedge or formally controlled bush and thin.

Remove all crossover branches and those that rub other branches.

Look at these leafless structures and just take in how thick it is.

Remove whole branches or secondary branches in order to thin that top-heavy growth.

Next lets move to your evergreens and discuss evergreen’s inherent dilemma.

All conifers require a slightly different approach. Most needled evergreens grow slowly from the branch tip.

Heading, if made behind this tip, only causes stubs or notches that are left not to grow back.

Approach evergreens as all other plants. First cut away all weak, broken, crossover branches.

Remove all errant growth and deadwood on the plant.

Now decide if you want the branches limbed up, or you looking for the gentle, ground-sweeping character?

Make all these cuts thinning cuts only. If you want limbs out of the driveway, then thin that limb way back into the primary or secondary branches (scaffold).

If you want that evergreen thick and lush and at the same time limit it’s growth rate, then you will head the newest growth.

During the growth season on pines, cut off half of the new candle(wrap new growth at tip seen roughly February to May) after it has elongated and turned slightly green.

Thicker evergreens

To make other evergreens thicker, make a series of minor thinning cuts.

By taking secondary tip branches back to a side shoot, you will reduce size and encourage thick new growth.

Next week, we’ll attack your shade trees and the orchard, so have a good bow or orchard saw ready.


Andrew May is an ornamental horticulturist who dreams of having Clallam and Jefferson counties nationally recognized as “Flower Peninsula USA.” Send him questions c/o Peninsula Daily News, P.O. Box 1330, Port Angeles, WA 98362, or email news@peninsuladailynews.com (subject line: Andrew May).

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