Pruning is a series of decisions, then a series of cuts.

The four things pruning can be

ANSI A300 names the objectives, and it is worth knowing them because they are what should appear on a written scope instead of “trim.”

• Cleaning removes dead, dying, broken and diseased wood. It is the lowest-risk pruning there is and it removes no live crown, so it does not count against the dose. Most trees need this and little else.
• Thinning selectively removes live branches to reduce density. Genuinely useful in a crowded, crossing canopy. Massively over-sold everywhere else, for reasons below.
• Raising removes the lowest branches for clearance over a drive, a walk or a roof. Careful with young trees — those low branches are what builds trunk taper.
• Reduction shortens limbs back to living laterals. That has its own page.

Lion-tailing, and why your tree looks like that

Stripping out the interior branches and leaving a tuft of foliage at the end of each limb is common, profitable and actively harmful. It is easy to sell because it looks tidy from the driveway and because somebody said the wind should “pass through.”

What it does is move all the weight and all the leverage to the far end of a limb, delete the interior foliage that was feeding the limb along its length, and expose bark that has never seen direct sun. The limb responds by pushing epicormic shoots from the stripped section, which are weakly attached, and the limb itself becomes more likely to fail, not less. A properly thinned tree still has leaves along the inside of its branches.

Where the cut goes

At the base of every branch is a swelling of overlapping trunk and branch tissue — the branch collar — and running up into the crotch is a raised seam called the branch bark ridge. Between them they mark the line. The cut goes just outside the collar, angled to follow it, leaving the collar intact and the wound as small as it can be.

Cut flush with the trunk and you have removed the collar, which is the tissue that grows the ring of callus over the wound. There is nothing left to close it with, so the decay column runs down into the stem. Leave a long stub and the stub dies back before the collar can reach it, with the same result and worse looks.

Anything heavier than an arm comes off in three cuts, not one: an undercut a foot or so out, a top cut beyond it so the limb falls without tearing, then the final cut at the collar on the remaining stub. Skip that and the limb peels bark down the trunk as it goes.

Dose, and the number to ask about

Roughly a quarter of a mature tree’s live crown is the working ceiling for one season, and less on a tree that is old, drought-stressed, root-damaged or recently moved. Dead wood does not count — it was not feeding anything.

Young trees tolerate more, and structural pruning on a young tree is the single highest-value thing anyone can do to it: choosing a leader, subordinating the competing stem, spacing the scaffold branches. Ten minutes with hand pruners at year five prevents the codominant union that needs cables at year thirty.

Timing, and no paint

Dead wood can come out any time. Heavy live pruning is best avoided during the spring flush, when the tree has spent its reserves and not yet got them back, and during a hard drought, when it cannot afford the water loss either. In practice, late winter is easy on most of what grows here.

No cut is painted, tarred or sealed. Dressings hold moisture against the wound and against the decay organisms that are already there, and a tree does not heal a wound — it walls the damage off internally and grows new tissue over it from the collar. Paint gets in the way of the second half of that and hides the cut from whoever inspects it next.