The best time to prune trees in western Oregon

The calendar

Scroll sideways on a phone. Dark green is the best window, pale green is fine, and red is best avoided.

Pruning calendar for the Beaverton area, by type of tree and month
Tree	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Most shade trees: oak, linden, elm, zelkova	Best	Best	Fine	Avoid	Avoid	Fine	Fine	Fine	Fine	Avoid	Avoid	Best
Maples and birches	Fine	Fine	Avoid	Avoid	Avoid	Best	Best	Best	Fine	Avoid	Avoid	Fine
Apples and pears	Fine	Best	Best	Avoid	Avoid	Fine	Fine	Fine	Avoid	Avoid	Avoid	Fine
Cherries, plums and other stone fruit	Avoid	Avoid	Avoid	Avoid	Fine	Best	Best	Best	Fine	Avoid	Avoid	Avoid
Spring-flowering trees: dogwood, magnolia	Fine	Fine	Avoid	Fine	Best	Best	Fine	Fine	Avoid	Avoid	Avoid	Fine
Douglas-fir, cedar and other conifers	Best	Best	Fine	Avoid	Avoid	Avoid	Fine	Best	Best	Fine	Fine	Fine
Arborvitae, laurel and other hedges	Avoid	Fine	Fine	Avoid	Fine	Best	Best	Fine	Avoid	Avoid	Avoid	Avoid
Oregon white oak	Best	Best	Fine	Avoid	Avoid	Avoid	Fine	Fine	Fine	Avoid	Fine	Best
Dead, broken or hazardous limbs	Best	Best	Best	Best	Best	Best	Best	Best	Best	Best	Best	Best

Best Fine Avoid. Timing is for the Tualatin Valley. A cold or early spring shifts everything by a few weeks.

A calendar like this is a guide to what is ideal, and it matters most for large cuts and heavy pruning. Taking a few small branches off a healthy tree in the wrong month does no lasting harm. Taking a third of the crown off at the wrong time can.

What kind of tree is it?

Pick yours for the window and the reason.

Which tree are you pruning?

Pick one and the answer appears here.

December through February.

With the leaves off you can see the structure, the tree isn't spending energy on growth, and it has the whole spring to begin closing its wounds. Light corrective pruning in summer is fine. Avoid the weeks when leaves are opening, when the tree's reserves are at their lowest.

Midsummer, or the first half of winter.

Maples and birches pruned in late winter drip sap for weeks. It looks alarming and does the tree no real harm. If it bothers you, prune in June through August once the leaves have hardened, or in December and early January before the sap rises. Birches stressed by bronze birch borer should be pruned as little as possible.

Late winter, February into March.

Prune for structure and fruiting wood while the tree is dormant, late enough that the worst of the cold and wet is past. Summer pruning in July and August is a useful second visit for controlling size and removing water sprouts, because it slows the tree instead of stimulating it.

In dry weather, June through August.

This is the biggest difference from advice written elsewhere. In our wet winters, fresh cuts on stone fruit invite bacterial canker and fungal diseases that enter through wounds and can kill whole limbs. Prune after harvest, in a dry spell, so the cuts dry and seal before the rain returns. The same applies to ornamental flowering cherries and plums.

Right after it finishes blooming.

These trees set next year's flower buds during summer. Prune in winter and you cut off the display. Prune in the few weeks after flowering and you get both good structure and next year's bloom. Dogwoods are prone to anthracnose in wet springs, so keep cuts small and tools clean.

Winter, or late summer.

Conifers are best pruned when they are not pushing new growth, which means avoiding April through June. Remove whole limbs back to the trunk. Conifers don't resprout from bare wood, so a branch cut halfway stays a stub. Pines can be kept compact by pinching the new candles in late spring, which is a separate technique.

Late spring to midsummer, after the first flush.

Shear once the spring growth has firmed up, usually in June, and again lightly in July if needed. Stop by early August, because growth pushed out late doesn't harden before frost. Laurel and photinia can be cut back hard in late winter. Arborvitae can't, since it won't regrow from brown wood.

Winter, and sparingly.

Our native oak needs little pruning beyond dead wood and clearance, and it is best done while dormant. Oregon doesn't have oak wilt, the disease behind the strict oak pruning seasons in the Midwest and Texas, so the timing is about the tree's energy, not infection. What happens on the ground under an oak matters far more than any pruning.

Why timing matters more here than elsewhere

Wet winters spread disease

From October to April, rain splashes bacteria and fungal spores onto every fresh wound, and cool temperatures mean the tree closes those wounds slowly. That is the reason behind summer pruning for stone fruit, and the reason autumn is the poorest season for large cuts on almost everything. Decay fungi release most of their spores in the fall rains.

Spring leaf-out is expensive

A tree spends its stored reserves pushing out leaves, and doesn't start earning them back until those leaves are full size. Heavy pruning in April and May removes the new leaves the tree has just paid for. Bark also slips and tears easily in spring.

Dry summers bring their own limit

July through September is reliably dry, which is good for wounds and hard on trees. Don't prune heavily during a heat wave or a drought year. A stressed tree needs every leaf it has.

Birds nest from March to July

Active nests of most native birds are protected by federal law. We check before we cut and work around a nest until the young have left, which is usually a matter of a few weeks.

How much, and how

When you prune matters less than how. A well-placed cut in the wrong month is better for the tree than a bad cut in the right one.

Cut at the branch collar, the swollen ring where a branch joins the trunk. Not flush with the trunk, and not leaving a stub.
Take no more than about a quarter of the live crown in a year, and much less from an old or stressed tree.
Never top. It doesn't matter what month it is.
Don't paint the wounds. Sealants don't prevent decay and can trap moisture.
Start young. A few small cuts in a tree's first ten years prevent the large, risky ones later.

The tree trimming page has a drawing of where a proper cut goes, and what flush cuts, stubs and topping do instead.

Three timing myths

"Prune in fall, once the leaves are down." It feels tidy, and it is the worst season for big cuts here: the wettest weather, the most fungal spores, and a tree that is shutting down and won't respond until spring. Wait until December.

"Never prune in summer." Summer is the right season for stone fruit, a good one for maples and birches, and a useful one for slowing an over-vigorous tree. The limit is heat and drought, not the calendar.

"It has to wait for the right month." Not if it is dead, broken, cracked or hanging. A hazardous limb over a roof or a walkway comes out the week you find it.

Questions people ask

When is the best time to prune trees in Oregon?

For most shade trees, December through February, while they are dormant. Cherries, plums and other stone fruit are the exception: prune those in dry weather from June to August. Dead and hazardous limbs can come out at any time.

Why shouldn't I prune my cherry or plum tree in winter?

In western Oregon's wet winters, fresh cuts on stone fruit let in bacterial canker and fungal diseases that can kill whole limbs. Pruning in a dry summer spell lets the wounds dry and seal before the rain returns.

Is it bad that my maple drips sap after pruning?

No. Maples and birches pruned in late winter bleed sap for a few weeks, and it does the tree no real harm. To avoid it, prune in midsummer once the leaves have hardened, or in December and early January.

Can I prune trees in the fall?

Small cuts and dead wood, yes. Large cuts are best avoided in October and November, when rain and fungal spores are at their peak and the tree is shutting down. Wait until the tree is fully dormant in December.

When should I trim an arborvitae hedge?

After the spring flush has firmed up, usually in June, with a light second trim in July if needed. Stop by early August so new growth hardens before frost. Never cut into bare brown wood, because arborvitae won't regrow from it.

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