Ask the Arborist: When should you top your trees? Never!

Topping is perhaps the most harmful tree pruning practice known. There is a reason Certified arborists are forbidden to top trees.  

“Topping” is the removal of a large portion of a tree’s crown to make it smaller and/or rounded. This misguided practice has reduced the lifespan and created hazardous situations of many shade trees throughout our community.

There are three basic rules for pruning shade trees:

1. Never remove more than 25% of the leaf surface area at one given pruning (annually).
2. When reducing the size of a limb, make sure that the lateral branch (the one that you intend to leave as the new end) is at least one-third the size of the branch that you are removing.
3. Never make a cut on a tree without a good reason (i.e. dead or rubbing limbs, branch level, house clearance, limbs with defects, etc).

“Topping” breaks ALL of these rules. Let me explain why.

The physiological process of a tree’s response to a topping cut is rather simple. The leaf surface produces food through photosynthesis. The woody portions of a tree (i.e. trunk, limbs, roots) use what they need and store the surplus. When a tree is in relatively good health (with adequate stored food) and it is topped, the tree will grow back rapidly (4-5 times its normal growth rate) until it recovers lost leaf surface. For example, Silver Maples grow between 12-16 inches each year. If you “top” it, the tree will respond by producing adventitious sprouts, commonly referred to as “suckers.” These suckers will grow 4-5 feet or more in the next season and continue at that rate until they reach the same size that it was before the damage. If the tree is not in good health when the damage is done, the tree may die outright. More frequently, the tree will begin a downward spiral of decline until it’s inevitable failure.

Secondly, the decay associated with the topping cuts is of even more concern. The vascular system of a tree, which transports water and nutrients, is located just beneath the bark. This is the area that a topped tree will produce the “suckers” to re-grow a canopy. These suckers are weakly attached to the side of the trunk! The sapwood and heartwood (innermost areas) will begin to decay. NOTE: Trees do not heal, they can only seal and hide their wounds. Now, the previously exampled Silver Maple has several suckers (4-8 or more) growing (4-5 feet or more) each year with decay developing between them. Ironically, most people top their trees because they think it will make them safer. The fact is TOPPING CREATES HAZARD TREES. Any defect on a tree will allow decay pathogens to invade and cause rot. There are many things that can cause these defects. Purposely creating these defects by topping your tree is not a good idea.

Finally, it’s not aesthetically pleasing. The natural beauty of a tree’s crown is a function of the uninterrupted taper from the trunk to even finer, more delicate branches. The strength of all trees to support their own weight is associated with taper also. Some species are weaker than others and this should be considered when determining what pruning specifications should be implemented, if any. Topping should certainly never be an option. If a tree is in such bad shape that topping is the only “safe” (I use this term ever so loosely) alternative, then the tree should be considered for removal.

Consider the length of time it takes for shade trees to get large. Many tree species last longer than people, some live past several generations. It is disturbing to everyone who loves trees to recognize that 90 years of growth, beauty and struggle to survive can be destroyed in a couple of hours.