What Is Crown Reduction and When Is It Used?

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Crown reduction means making the crown of a tree smaller while keeping its natural shape. Not cutting it off at a height — reducing it, evenly, all over, so that afterwards it looks like the same tree, smaller.

How It Is Actually Done

Each branch being shortened is cut back to a point where there is a suitable side branch to take over as the new leading growth. That side branch needs to be big enough relative to the wood being removed — the convention is roughly a third of the diameter — because it now has to draw the sap and seal the wound.

Work through the whole crown doing that, and the tree ends up perhaps a couple of metres smaller in every direction, with an outline that still reads as a tree of that species.

Why This Is Not Topping

Topping is cutting the main stems off at a convenient height, without regard to what is growing there. It is quicker and cheaper and it produces a dramatic result, which is why it still gets sold.

What it leaves is a set of stubs with no growth point to take over. The tree responds to losing most of its leaf area by throwing out a mass of fast vertical shoots from dormant buds just below the cuts. That regrowth is:

• Attached to the outside of the old wood rather than growing from the structure, so it is weakly held and prone to tearing out
• Faster than the original growth, so the tree is back to its previous height in a few years, denser and heavier than before
• Growing out of a wound the tree cannot seal, because a stub cut into old wood has no mechanism to close over. Decay gets in behind it

There is a narrow and legitimate exception: pollarding, where a tree is cut back to the same points on a regular cycle, starting when the tree is young. A pollard maintained properly from the beginning is a long-lived, stable form. It is not the same as topping a mature tree once and walking away.

When Reduction Is the Right Answer

• The crown has grown over a roof, a conservatory or a boundary
• The tree is casting more shade than the garden can carry
• It is in an exposed position and the wind loading is a concern
• A long lateral limb is carrying too much end weight
• The tree is large enough that its scale has become uncomfortable relative to the house

How Much Can Come Off

As a rule of thumb, up to around a quarter to a third of the crown in one go on a healthy tree. Beyond that you are into territory where the tree's response is a stress response rather than normal growth, and where finding suitable growth points to cut back to becomes difficult — which is the point at which reduction quietly turns into topping.

Older trees tolerate less. A very mature specimen is better given a light reduction repeated over years than a heavy one in a single visit.

The Related Techniques

• Crown thinning — removing a proportion of the branches throughout the crown without changing its size or outline. This is the one for light, and it does not make the tree smaller
• Crown lifting — removing the lowest branches to raise the clearance underneath. Useful over a path, a drive or a lawn
• Deadwooding — taking out the dead material and leaving the live crown alone. Often the whole answer where the concern is things falling

Quite often somebody asks for a reduction when thinning or lifting is what would actually solve their problem, and it is worth saying so — both are less work and less intervention.

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