How Topping Hurts Trees

We’ve written about tree pruning before, but today we had a chance to see clear examples of how poor pruning techniques are harmful to our front yard trees and our street trees, while talking a walk with arborist Cy Carlberg and garden designer Judy Horton.

In the winter when leaves have fallen, it’s easier to see the effects of topping trees, the practice of cutting off the tops of tree branches or rounding the tree that leaves stubs where branches once grew. This Crepe Myrtle was severely topped at one point, as evidenced by the spiky stubs at the top of the tree.

Once the tree starts to grow back and the leaves fill in, you look at the inside branches to see how the harsh pruning harms the tree forever. The inside branches in this Jacaranda look very different from the rest of the tree, and the balance and structure of the tree is jeopardized because the tree was topped, forcing new growth to pop out unevenly.

Below are examples of trees that have been allowed to grow naturally without harsh pruning. The classic structure of these elegant trees looks beautiful even without any leaves!

Horton noted that most trees need very little pruning, not more than ten percent of the tree annually.

“Most of us have trees that were planted before we moved in,” explained Horton.  “Many of these trees were planted shortly after the house was built. Often, we take these trees for granted and that can be good for them, as once a tree is well established there is seldom need to fertilize or water it. In fact, fertilizer and overwatering can do harm.”

Here are some suggestions Horton prepared for her clients and shared with us.

In the case of trees, what not to do in the garden is more important than what to do. Here are the basics:

• If the tree is healthy, leave it alone. Trees hate change.
• Always use a certified arborist for any tree care. Trees should be laced out, not topped.
• Mature trees do not need supplemental water except in times of drought, and no fertilizer unless to correct a deficiency.  Either should be administered by a certified arborist.
• Know the tree’s growing season.
• Check with a soil probe during times of drought. If the soil is bone dry, irrigate with a soaker hose to the depth of at least 12” during the tree’s growing season.
• The root crown (base of trunk) is a vulnerable area. Never leave dirt, debris or mulch piled against the trunk and do not allow water to collect on or near the root crown.
• Do not till soil or plant anything other than ground cover under the drip line.
• Keep lawn and groundcover well away from the trunk.
• Tree roots are in the top 12-24” of soil and extend well beyond the drip line (the outermost area of the tree canopy (foliage).
• Protect your trees during construction, following the advice of a certified arborist. Construction anywhere in the root area can cause harm. The harm comes from soil compaction due to heavy equipment; mechanical injury of roots, trunks or branches; change of grade either exposing roots or suffocating them by raising soil level.

If a tree shows stress – such as change in color or the dying of some branches – call a certified arborist for diagnosis. Unfortunately, by the time that stress is visible, it is often too late. Damage during construction or during drought may not show up for 2-3 years, and by then it may be impossible to reverse. 

How does one know when to water? The only sure way is to check the soil to a depth of about 15” with a soil probe. With a soil probe or sampler, you take a core of soil out and examine it. Most often you will find wet gummy soil, a sign to cut back on irrigation. But in times of low rainfall, especially after 2 or more years of drought, you could find dry, dusty dirt.

The best way to water trees is with soaker hoses wrapped around the tree at the drip line, and left on for several hours. After a session with the soaker hose, wait one day then test the soil again to make sure the water penetrated to 12-16”. Do not water trees when they are dormant. Most trees are winter dormant, but California natives are summer dormant.