Yes — Strong Match
plains coreopsis is grown in zones 2-11, which covers every zone Washington contains (4a-9b). Whether the season is long enough is the question that remains.
Plains Coreopsis in Washington — the short answer
Plains Coreopsis in Washington: grown in zones 2–11, full sun, against a state median of ~208 frost-free days.
- Plant zones
- Grown as an annual — see the growing season
- Growing season, not a hardiness zone
- Washington zones
- 4a-9b
- USDA PHZM 2023
- Frost window
- Mar 16 - Apr 15 – Oct 24 - Nov 18
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 131 days
- NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — per-field provenance varies and is published with the dataset.
Your yard isn't the whole zone.
Plains Coreopsis is grown as an annual, so your winter zone isn't the deciding factor — your frost-free window is. A typical Washington site runs ~208 frost-free days, but that is a state median, not your yard: slope, trees, and low spots move the last-frost date across a single parcel. Enter your address and we'll score plains coreopsis against your land's actual frost dates, sun, and soil.
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Washington is not one climate
A single Washington answer averages 39 counties whose growing seasons are 169 days apart — from 131 frost-free days in Whatcom County to 300 in San Juan County. Which end of that your land sits nearer changes what plains coreopsis can finish before the first hard freeze.
The middle half of 39 counties runs 192–248 days, with a median of 208 days — a 169-day span end to end.
Measured across 39 Washington counties. NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze. Quartiles are order statistics — every figure shown is a value a real county recorded, not an interpolation. Your own site sits somewhere inside this range; a parcel report resolves where.
Where in Washington Fits Best
Even within Washington's zones 4a-9b, county microclimates differ enough to change what thrives. These counties carry the closest zone match for plains coreopsis (USDA PHZM 2023):
Zone Comparison
Plains Coreopsis Needs
- USDA Zones: 2-11
- Sun: Full Sun
- Mature size: 3 ft tall
- Picking window: ~60 days of harvestWe haven't confirmed this against a published source yet.
- Drought tolerance: Low
Washington Has
- USDA Zones: 4a-9b
- Last Hard Freeze (28°F): Mar 16 - Apr 15
- First Hard Freeze (28°F): Oct 24 - Nov 18
- Annual Rainfall: 6-90 inches
- Common Soils: Volcanic ash, Silt loam (Palouse), Sandy loam
Plant Zone Range (zones 2-11)
Preferred Soil pH
We haven't confirmed this against a published source yet.
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS, and university Extension sources — per-field provenance varies and is published with the dataset. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Plains Coreopsis in Washington
The frost window
Across Washington, the last spring hard freeze (28°F) clears between Mar 16 and Apr 15, and the first fall hard freeze lands between Oct 24 and Nov 18 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 192-day window you can count on — up to 247 days on a mild site in a kind year. That marks the hard freeze, not the last light frost, so tender transplants usually wait another 2-3 weeks.
When to start the seed
Those dates are when plains coreopsis goes out, not when it starts. It is sown under cover about 6 weeks ahead, so counting back from Washington's late-side last freeze of Apr 15 is what fixes your sowing date — and a yard that clears frost earlier than the state's late date starts earlier still.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: Growable Ground Plant Database — frost-free days from FAO ECOCROP, days to harvest from university Extension production guides, and growing-degree-day and chill-hour minimums that are compilation estimates rather than published figures. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Soil + Drainage Fit
Plains Coreopsis likes near-neutral soil (pH 5.5-7.5). That's the common-ground band across Washington's volcanic ash and silt loam (palouse) — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 6 and 7 — worth knowing before you decide whether a Washington soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Washington site is heavier clay or sits in a low spot, a raised bed lifts the roots above wet ground, or work in compost. pH range and preferred pH: We haven't confirmed this against a published source yet.
Plant pH requirements: FAO ECOCROP and USDA PLANTS, with the remaining rows from other published sources or Growable Ground compilation. Drainage: FAO ECOCROP, with the remaining rows from other published sources or Growable Ground compilation. Washington soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
What Else to Consider for Plains Coreopsis in Washington
The zone range tells you where plains coreopsis is grown — but Washington growers also need to think about:
Extreme rain divide: 90+ inches west, 6 inches east of Cascades
East side requires irrigation — no rain from June through September
Slug and root rot pressure on the wet west side
Short seasons at elevation in the Cascades and northeast corners
What to actually do about these — and the constraints that apply to every Washington grower, not just plains coreopsis — is covered on the Washington growing guide.
Where in Washington Plains Coreopsis Is Zone-Hardy
Plains Coreopsis is rated for USDA zones 2–11. Every one of Washington’s 39 counties sits inside that band — from Ferry County at zone 6a to San Juan County at zone 9a — so winter cold is not what decides this plant anywhere in the state. What is left to vary is your own parcel: slope, shelter and cold-air drainage routinely move a site half a zone either way from the county figure.
Across those 39 counties Washington’s winter-low ladder runs from zone 6a in Ferry County to zone 9a in San Juan County — 3 USDA zones of spread, which is 30°F between the two counties’ average coldest night of the year. That is why a statewide hardiness answer is where you start and not where you finish.
The planting window moves with it. Whatcom County holds its last hard freeze (28°F) until about May 29, while Island County is clear by Feb 8 — 110 days apart. Set plains coreopsis out on your county’s date, not the state’s.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. County last-freeze dates: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F killing freeze — earlier than the folk 32°F "last frost". Plains Coreopsis’s zone 2–11 band: a season crop, no zone claim. A parcel report resolves your address’s own zone and frost dates rather than its county’s.
Pollinator + Wildlife Value
Plains Coreopsis draws honeybees, native bees, and butterflies (high value). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, plains coreopsis can only work that bloom inside Washington's frost window — roughly 208 days, opening after the last 28°F freeze (Mar 16 - Apr 15) and closing at the first (Oct 24 - Nov 18), per NOAA Regional Climate Centers ACIS, 1991-2020. Pollinator value: We haven't confirmed this against a published source yet.
Washington Cooperative Extension
For Washington-specific cultivar recommendations, planting calendars, and pest pressure for plains coreopsis, the canonical source is WSU Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Plains Coreopsis native to Washington?
The USDA PLANTS Database (accessed 2026-10-19) lists Plains Coreopsis as native to the Lower 48 and records it growing in Washington, but it does not say whether those Washington plants are native or introduced. Your state's native plant society or Cooperative Extension can tell you whether it is part of the local flora.
State records: USDA PLANTS Database state-distribution data (presence, not state-level nativity), accessed 2026-10-19.
Common Questions About Growing Plains Coreopsis in Washington
When can I plant Plains Coreopsis in Washington?
Washington's last spring hard freeze (28°F) clears between Mar 16 and Apr 15, and the first fall hard freeze lands between Oct 24 and Nov 18 (NOAA Regional Climate Centers ACIS, 1991-2020). Time outdoor planting to after the last hard freeze for your specific site — a further two to three weeks for anything tender — and count back from those dates for transplant scheduling.
What hardiness zone is Plains Coreopsis grown in across Washington?
Washington spans USDA hardiness zones 4a-9b (USDA ARS PHZM 2023). Plains Coreopsis carries a range of zones 2-11, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Washington site have?
A typical Washington site sees ~208 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Plains Coreopsis should be matched against that window, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Plains Coreopsis native to Washington?
The USDA PLANTS Database (accessed 2026-10-19) lists Plains Coreopsis as native to the Lower 48 and records it growing in Washington, but it does not say whether those Washington plants are native or introduced. Your state's native plant society or Cooperative Extension can tell you whether it is part of the local flora.
How should I amend the soil for Plains Coreopsis in Washington?
Plains Coreopsis prefers pH 5.5-7.5 and well (dry spells) drainage. We haven't confirmed this against a published source yet. That sits in the common-ground band across Washington soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Plains Coreopsis actually grow on my specific land in Washington?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores plains coreopsis against your address's mapped soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in Washington
State-level data is a sketch. Your Growable Ground report scores plains coreopsis against your land's mapped soil, modelled sun, drainage, and frost data — not zone averages.
Three things about your lot that Washington plains coreopsis averages can't show:
We read public map data around Washington — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Washington plains coreopsis average
Explore More
Growing guides for plains coreopsis
Explore Washington county by county
Washington carries 39 counties with their own USDA zone — a sample of the growing pages for plains coreopsis there:
Where else plains coreopsis grows
Plains Coreopsis's zone band crosses state lines — these are the states closest to Washington in winter climate where it also has a page, plus the far ends of its range. Each one re-answers the question with that state's own record.
More to grow in Washington
Washington has a growing page for 1,033 plants — a rotating sample of the rest of the shelf.
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