Best time to plant trees in the Pacific Northwest

When is the best time to plant trees west of the Cascades?

Portland and Seattle say nearly the same thing. Portland’s Urban Forestry program recommends planting from October 1 through April 30 and advises against planting from May 1 through September 30; trees that do go in during summer need extra water to survive and establish. Seattle’s tree program calls fall the best time, because trees planted from October to December use the fall and winter rains to build roots before the next summer dry spell.

The rain calendar explains it. At Portland International Airport, NOAA’s 1991–2020 normals put 27.32 of the year’s 36.92 inches in October through March, while July and August together average 1.05 inches. Plant in May and the tree heads straight into the driest months, which is why Portland asks for extra watering on summer plantings.

The International Society of Arboriculture (ISA) puts the ideal window in the dormant season everywhere: fall after leaf drop, or early spring before bud break, when cool weather lets roots establish before summer heat pushes new top growth. Healthy container and balled-and-burlapped trees can go in throughout the growing season, ISA adds, though Portland asks for extra water on any summer planting. OSU Extension calls fall planting “a counterintuitive but useful tool” for keeping stress off a new tree, and its October garden checklist says to plant trees and shrubs.

When to plant trees in Oregon and Washington, east and west of the Cascades

East of the mountains the rain math changes. Spokane averages 16.45 inches of precipitation a year and Bend 10.62, and neither gets a wet fall that does the watering for you: Spokane’s October normal is 1.37 inches, Bend’s 0.65. ISA’s dormant-season windows still apply there, early fall after leaf drop or early spring before bud break, but every new tree will need a hose. Spokane’s Urban Forestry program puts the growing season at April to late October and says to keep watering new trees until mid-fall, tapering off as it cools.

Source: NOAA NCEI U.S. Climate Normals 1991–2020, monthly precipitation; stations Seattle-Tacoma Intl Airport (USW00024233), Portland Intl Airport (USW00024229), Salem McNary Field (USW00024232), Medford Rogue Valley Intl Airport (USW00024225), Spokane Intl Airport (USW00024157), Yakima Airport (USW00024243) and Bend (USC00350694). Computed by Westcoast-Tree.org, checked 2026-10-02.

The west-side cities get about three-quarters of their precipitation from October through March, so winter rain does most of the watering for a fall planting. The east-side stations get far less in total and a smaller share of it in winter, so plan the irrigation along with the planting date.

Are Northwest summers getting drier?

Compared with the 1981–2010 normals, the 1991–2020 normals show a wetter October at all five stations below and a drier July and August at four of them; Seattle’s midsummer total barely moved. The two periods share the years 1991 through 2010, so the change reflects swapping the 1980s for the 2010s. Treat it as a nudge toward fall planting, not proof of a trend.

Source: NOAA NCEI U.S. Climate Normals, 1981–2010 and 1991–2020 monthly precipitation (inches), same stations as above. Checked 2026-10-02.

Bare-root, container or balled-and-burlapped: when to plant each

Nursery trees come three ways, and the type changes both the timing and the prep. ISA’s guide to buying trees describes each; the planting windows below combine ISA’s advice with Portland’s and Seattle’s seasons.

Sources: ISA, Buying High-Quality Trees and New Tree Planting; City of Portland; City of Seattle. Checked 2026-10-02.

How to plant a tree, step by step

These steps follow ISA’s New Tree Planting guide and the planting instructions from Portland’s and Seattle’s urban forestry programs. They agree on what matters most: a wide, shallow hole, the root flare at ground level, the native soil going back in, and mulch kept off the trunk.

1. Call 811 two business days aheadBoth states require a locate request before most digging; the rules are in the 811 section below.
2. Find the trunk flareThe flare is where the trunk widens into the first big roots. If it’s buried in the pot or root ball, scrape off soil from the top until you see it.
3. Dig wide and shallowMake the hole 2–3 times as wide as the root ball and only as deep as it, so the ball rests on undug soil.
4. Unwrap and fix the rootsRemove the pot, and take as much burlap, twine, plastic and wire as you can from the top and sides of a B&B ball; ISA says to remove the wire basket or cut off one or two top rings. Straighten, cut or remove circling roots, and pull out bamboo stakes and nursery tags.
5. Set the heightLift by the root ball, not the trunk. The flare should sit at or slightly above grade and stay partly visible; most of a tree’s roots grow in the top 12 inches of soil, and planting too deep harms it.
6. Backfill with the soil you dug outSkip compost and fertilizer in the hole; Portland allows amendments only in very poorly drained or heavily urbanized soil. Break up clods and water as you fill to settle out air pockets. Seattle says to firm the soil in; Portland warns against over-compacting.
7. Water it inSoak the backfill and root ball right after planting, then start the weekly schedule in the watering section.
8. Mulch, but not the trunkSpread 2–4 inches of mulch in a circle about 3 feet out from the trunk, and keep it a few inches off the bark. Seattle suggests bark mulch or arborist wood chips; see where to get free wood chips.
9. Stake only if it won’t standMost trees don’t need stakes. ISA notes that unstaked trees grow stronger trunks and roots, though bare-root trees and windy sites may need support. Remove stakes after about a year.
10. Hold off on pruningIn the first year, cut only dead or broken branches. ISA says to wait until the second or third year for structural pruning.

How much to water a new tree the first three summers

OSU Extension notes that people often underestimate how much and how often a newly planted tree needs water. The local programs put numbers on it:

Sources: City of Portland, Establishment care; City of Seattle, Young tree care; Friends of Trees, Summer tree care in the Pacific Northwest (July 7, 2026); City of Spokane, Tree watering quick guide. Checked 2026-10-02.

In practice that means a slow, deep soak once or twice a week from late spring into fall for at least the first two or three summers, with extra rounds during heat waves. Check before you water: Friends of Trees suggests pushing a pencil about two inches into the soil to see whether water is reaching the roots, and Spokane’s guide uses a finger test, where soil that sticks to your fingers means you can wait.

The payoff grows with the tree. i-Tree, the USDA Forest Service’s tree-benefit software, assigns each tree its share of avoided stormwater runoff in proportion to its leaf area, and treats leaf area as a key input for air-pollution removal and carbon storage. A tree that dies young never builds that leaf area.

Call 811, check street-tree permits and pick the right spot

Both states require a locate request through 811 before you dig, with only narrow exceptions, and Oregon’s 811 center names tree planting as a reason to call.

Street trees need a permit in Portland and Seattle

Portland requires a permit to plant any tree in the city right-of-way, usually the strip between curb and sidewalk; planting on private property needs no permit. Seattle asks for a free planting permit from the Seattle Department of Transportation’s Arborist Office, and whoever plants the street tree takes on its care, including summer watering. Removing a tree later is a separate question, covered in the Oregon tree removal permit guide and the Washington tree removal permit guide.

Free trees in Portland and Seattle

Portland’s Trees for Your Yard program gives residents up to three free trees, with registration opening each September for fall pick-up events around the city. The city also plants free street trees, with three years of watering, in planting strips at least 4 feet wide in the neighborhoods with the fewest trees (staff contact eligible owners), and it partners with Friends of Trees on free plantings in select neighborhoods. Seattle’s planting page points residents to its Trees for Neighborhoods program; check that page for this season’s sign-up.

Right tree, right place

ISA’s utility guidance splits a yard into zones by distance from distribution lines: within 15 feet, choose trees that top out at 20 feet or less; from 15 to 50 feet, 40 feet or less; and keep large species at least 50 feet away. The utility tree trimming pages show who trims near lines in each service area, and the guide to telling whether a tree is too close to your house covers mature size against walls and roofs. Check winter cold with the Washington and Oregon hardiness zone lookup, and for species picks see the best privacy trees for the Northwest or Japanese maple care.

If the new tree is replacing one that came down, the old stump sits in the obvious spot. Stump grinding clears it so you can plant close to where the old tree stood.