At a glance
- Region ID: PNW
- Anchor cities: Seattle, Portland
- USDA Hardiness Zones: 8a–8b
- Climate: Maritime — cool wet winters, mild dry summers, extended overcast
- Catalog size: 89 plants
- Climate factors: Year-round moss and lichen pressure, slug capital of the US, excellent conditions for hydrangeas, Japanese maples, rhododendrons, and conifers
Pruning & maintenance calendar
January – February
March – April
Forsythia and spring-blooming shrub pruning after bloom. Hydrangea dead wood cleanup. Slug bait deployment — iron phosphate baits down before spring growth surge.
May – June
July – September
Japanese maple pruning window — sap movement lowest. Bigleaf hydrangea post-bloom pruning. Dry season = reduced disease pressure across all species.
October – November
Fall cleanup. Moss treatment on hardscapes. Prepare for wet season — ensure drainage is clear, reduce mulch depth where slug pressure is heavy.
December
Minimal activity. Wet conditions limit site access. Structural inspections of mature trees during storms.
Regional pest & pathogen pressure
- Slugs — year-round, the defining regional pest. Devastating on hosta, bedding plants, and young transplants. Iron phosphate baits are the primary control.
- Boxwood blight — pressure heavy. Wet maritime conditions are ideal for the pathogen (Calonectria pseudonaviculata). Dark leaf spots, rapid defoliation, black stem streaking.
- Anthracnose on dogwood and maple — chronic in wet springs. Dogwood anthracnose pressure heavy in coastal conditions; performs better inland.
- Powdery mildew on crape myrtle and roses — chronic in the maritime climate. Limits crape myrtle bloom production compared to Southeast.
- Black spot on roses — wet conditions favor year-round pressure.
- Root rot (Phytophthora) — wet winter soils; drainage critical for susceptible species.
- Moss and lichen on hardscapes and woody plants — cosmetic but universal. Clients frequently mistake it for disease.
- Apple maggot and spotted wing drosophila on fruit trees — common in residential landscapes with edible plantings.
Core staples (commonness 1)
Currently: 12 of 89 plants profiled. Remaining plants tracked in the catalog data.
Red Maple
Core staplePruning — late winter during dormancy
Reliable shade tree across the PNW. Fall color variable but generally good. Site in well-drained soils — surface roots develop at maturity and can heave hardscape.
Common pathogens
Disease Anthracnose
Chronic in wet springs. Irregular brown leaf spots and premature defoliation. Trees typically recover with warmer dry weather — rarely fatal but visually alarming to clients annually.
Crape Myrtle
Core staplePruning — late winter, before bud break
Marginal climate for crape myrtle. Powdery mildew is chronic in the maritime climate — bloom production is lighter than in the Southeast. Cold-hardy cultivars survive, but this is not a plant that thrives here. National Arboretum "Indian Tribes" series bred for mildew resistance. Never top.
Common pathogens
Disease Powdery mildew
Chronic in the PNW maritime climate. White powdery coating on leaves and flower buds. Reduces bloom production significantly compared to warmer, drier regions.
Flowering Dogwood
Core staplePruning — after bloom, May–June
Anthracnose pressure heavy in coastal PNW conditions — performs better at inland sites with more air circulation. Kousa dogwood (C. kousa) is the more disease-resistant alternative frequently specified in the region. Site in well-drained soil with afternoon shade protection.
Common pathogens
Disease Dogwood anthracnose
Leaf spots, twig dieback, and cankers — can be fatal in severe cases. Pressure heaviest in wet coastal conditions with poor air circulation. Inland sites with good drainage fare significantly better.
Japanese Maple
Core staple · Climate-idealPruning — late summer (July–September)
PNW produces the best Japanese maple plantings nationally. The maritime climate — cool wet winters, mild dry summers — is near-ideal for the species. Hundreds of cultivars available from regional specialty growers. Prune in late summer when sap movement is lowest to minimize bleeding. Avoid heavy pruning — the species' natural form is the point.
Cultural notes
The signature small tree of Pacific Northwest residential landscapes. Laceleaf (dissectum) forms for understory and specimen plantings; upright forms for structure and screening. Fall color exceptional in the PNW climate. Protect from hot afternoon sun in eastern exposures — leaf scorch is the primary cultural issue.
Green Giant Arborvitae
Core staplePruning — late spring to early summer shearing
Reliable screening and privacy tree in well-drained sites. Fast growth rate (3–5 ft per year when young). Drainage is critical — Phytophthora root rot in wet winter soils is the primary failure mode. Deer-resistant. Tolerates shearing well for formal hedging.
Camellia (Sasanqua)
Core staplePruning — immediately after bloom (January–February)
Performs well in PNW maritime conditions. Fall and winter bloom provides off-season color when most of the landscape is dormant. Site in well-drained acidic soil — the same conditions that suit rhododendrons.
Common pathogens
Disease Algal leaf spot
Moderate pressure in wet conditions. Raised green-to-orange spots on leaf surfaces. Cosmetic primarily — rarely affects plant health. Improved air circulation reduces incidence.
American Boxwood
Core staplePruning — late spring to early summer
Boxwood blight pressure is HEAVY in the PNW. Wet maritime conditions favor the pathogen (Calonectria pseudonaviculata) year-round. Dark leaf spots, rapid defoliation, and black streaking on stems. Remove and destroy affected plants — do not compost. Blight-resistant cultivars (NewGen series) or alternatives like Japanese holly (Ilex crenata) and Distylium are increasingly specified.
Common pathogens
Disease Boxwood blight
The defining disease of boxwood in the PNW. Spores spread in wet conditions and persist in soil and leaf litter for years. Once established in a site, replanting boxwood is not recommended.
Bigleaf Hydrangea
Core staple · Climate-idealPruning — after bloom (July–August)
Near-ideal climate — bloom production exceptional in the PNW. Blooms on old wood; late pruning removes next year's flower buds. The acidic soils common in the region produce blue flowers naturally. Protect from afternoon sun in eastern exposures. Endless Summer and similar reblooming cultivars provide extended color.
Cultural notes
The PNW produces some of the best hydrangea displays in the country. Flower color is pH-dependent — acidic soil (common in PNW) = blue; alkaline = pink. Aluminum sulfate amendments push color bluer.
Panicle Hydrangea
Core staplePruning — late winter, before new growth
Reliable in the PNW. Blooms on new wood — prune in late winter without risk to flower production. Limelight and Little Lime are the most commonly specified cultivars. More sun-tolerant than bigleaf hydrangea.
Common pathogens
Disease Bacterial leaf spot
Moderate pressure in wet springs. Angular water-soaked spots on leaves. Improve air circulation; avoid overhead irrigation.
Knock Out Rose
Core staplePruning — after Presidents' Day (traditional PNW timing)
Rose rosette virus (RRV) present but lower pressure than in the Southeast and Midwest. Black spot is the more frequent issue in the PNW — wet conditions favor it. Prune hard in late winter (after Presidents' Day is the traditional PNW timing). Remove and destroy any plant showing RRV symptoms: witches' broom, excessive thorniness, distorted red growth.
Common pathogens
Disease Black spot
Circular black spots with fringed margins; yellowing and defoliation. Wet conditions favor — chronic pressure through the rainy season. Good air circulation and morning sun exposure reduce severity.
Disease Powdery mildew
White powdery coating on new growth. Chronic in PNW conditions.
Hosta
Core stapleMaintenance — spring through fall
Slug pressure YEAR-ROUND — the defining management challenge for hosta in the PNW. Climate is otherwise ideal: cool summers, consistent moisture. Iron phosphate baits (Sluggo) are the primary control. Evening hand-picking during peak activity. Reduce mulch depth around hostas to limit slug habitat. Thicker-leaved cultivars (Sum and Substance, Blue Angel) show better slug resistance than thin-leaved varieties.
Common pests
Pest Slugs
The defining pest-plant interaction of the PNW. Irregular holes in leaves, slime trails. Pressure is year-round — not seasonal. Every hosta planting in the region requires an active slug management program.
Liriope / Monkey Grass
Core staplePruning — late winter (February–early March)
Reliable in shade — workhorse border and groundcover plant. Mow or string-trim entire planting to 2–3 inches before new growth.
Common pathogens
Disease Anthracnose
Pressure in wet winters. Reddish-brown leaf spots and tip dieback. Cut back hard in late winter to remove infected foliage before new growth emerges.
Inside the app
Skip the spreadsheet. Verdant Meridian seeds your library with the regional palette on day one.
Pick your region at onboarding — the app loads commonness-1 and commonness-2 plants into your element library.
Try Free — 30 DaysHow this list was built
Compiled from regional wholesale grower availability lists — not retail garden references. No chemical, fungicide, or product recommendations appear anywhere in this database. Diagnostic and cultural information only.
FAQ
Can you grow crape myrtle in Seattle?
Marginal. Powdery mildew is chronic in the maritime climate, and bloom production is lighter than in the Southeast. Cold-hardy cultivars survive, but crape myrtle will never perform in Seattle the way it does in Atlanta or Charlotte.
What is the best tree for a small yard in Portland?
Japanese maple. The Pacific Northwest produces the best Japanese maple plantings nationally — the maritime climate is near-ideal. Hundreds of cultivars available from regional specialty growers. Prune in late summer when sap movement is lowest.
Why is my boxwood dying in the Pacific Northwest?
Most likely boxwood blight. The wet maritime conditions are ideal for the pathogen — spores spread in wet conditions and persist in soil and leaf litter. Remove and destroy affected plants; do not compost. Consider Ilex crenata or Distylium as alternatives.
When should I prune hydrangeas in the Pacific Northwest?
Depends on the type. Bigleaf hydrangea (H. macrophylla): prune after bloom in July–August — it blooms on old wood. Panicle hydrangea (H. paniculata): prune in late winter — it blooms on new wood.
How do I control slugs in my garden?
Year-round pressure in the PNW. Iron phosphate baits (Sluggo) are the most effective broad control. Supplement with evening hand-picking. Reduce mulch depth to limit habitat. Copper barriers around raised beds provide a physical deterrent.
Cite this page
Verdant Meridian, “Pacific Northwest Plant Palette,”
verdantmeridian.app/regions/pacific-northwest, updated May 2026. CC-BY-4.0. Raw data: /data/plants.json.Published under CC-BY-4.0. Free to use, redistribute, build on — attribution required.
