How much of a tree can be pruned at one time?

The number and where it comes from

The 15 to 20 percent figure is from UNR Extension's fruit-tree guide for Northern Nevada, which says to avoid removing more than that share of a mature tree's live wood, and that dried-up dead wood is not counted. It is written for fruit trees. We use it as a sensible ceiling for other mature deciduous trees too, and we say so because the guide does not claim it for every species.

Conifers are a separate case: a pine, spruce or juniper will not regrow from bare old wood, so an arborist takes even less live crown and leaves the green growth that carries the tree.

Why more is not better

Leaves feed the tree and the roots. Strip a large share of the crown at once and the tree draws on stored energy it may not be able to replace, especially in a dry year. The ISA also advises avoiding heavy cuts to live tissue right after the spring growth flush.

The usual response to over-pruning is a thicket of fast, weak shoots from the cut ends. See why water sprouts grow after pruning.

What a big tree needs instead

If a tree is too large for its spot, cutting it back to stubs is topping, and ANSI A300 advises against it. A better plan spreads the work. Dead wood can come out in one visit. Reduction of the longest limbs, cut back to a lateral branch large enough to take over, can follow in another season. Thinning, raising and reduction each have a different limit.

Sometimes the honest answer is that the tree no longer fits the site, and removal is cleaner than a series of heavy cuts.

Ask for the numbers at the estimate

A good plan says which limbs come off and roughly how much of the live crown that is. The arborist who walks the tree sets the amount, and the free estimate is the time to ask. Our office number is 775.232.8243.

A note on species

Different trees take different amounts. Fast, soft-wooded trees such as cottonwood bounce back more readily than slow pines or junipers. The figure here is a ceiling, not a target.