Generally — Most Areas
blue vervain (zones 3-8) suits most of Washington (4a-9b) — zones 4-8 are in range, and the rest of the state is the exception.
Blue Vervain in Washington — the short answer
Blue Vervain in Washington: hardy in zones 3–8, against a state median of ~208 frost-free days.
- Plant zones
- 3-8
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- 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.
Washington spans zones 4a-9b, but your yard sits in exactly one — and slope, tree cover, and cold-air pockets nudge it further. Enter your address and we'll score blue vervain against your parcel's actual hardiness, soil, and sun.
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Washington is not one climate
Washington’s winter-low ladder runs across 39 counties, from zone 6 in Ferry County to zone 9 in San Juan County. That is 30°F between the two counties’ average coldest night — the difference between blue vervain overwintering in the ground and coming under cover.
The middle half of 39 counties runs 7–8.5 zones, with a median of 7 zones — a 3-zone span end to end.
Measured across 39 Washington counties. USDA PHZM 2023, per county. 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
Blue Vervain is rated for zones 3–8 — a cold floor USDA puts at -40 to -30°F. Against Washington’s 39 counties that band holds in 26 of them, and the line runs at Ferry County (zone 6a), the coldest county still inside it.
Inside zones 3–8
26 counties
- Okanogan County · zone 6a
- Pend Oreille County · zone 6a
- Douglas County · zone 6b
3 of 26 shown
Above the zone 8 ceiling
13 counties
- Clallam County · zone 8b
- Clark County · zone 8b
- Cowlitz County · zone 8b
3 of 13 shown
Too little winter chill rather than too much cold — a low-chill selection is what changes it.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. A zone is a 10°F band of average annual extreme minimum temperature, so the floor above is the band the plant's rating denotes, not a single measured kill point. Slope, shelter and cold-air drainage routinely move a site half a zone either way from its county figure — which is the part only your address resolves.
Even within Washington's zones 4a-9b, county microclimates differ enough to change what thrives. These counties carry the closest zone match for blue vervain (USDA PHZM 2023):
Zone Comparison
Blue Vervain Needs
- USDA Zones: 3-8
- Mature size: 5 ft tall
- Picking window: ~45 days of harvest
- 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 3-8)
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 Blue Vervain 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.
Winter standing
Washington runs as cold as USDA zone 4, and no sourced winter-hardiness floor is on record for blue vervain, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether blue vervain is a permanent planting or a replant-every-spring crop for you turns on your own zone within Washington; check its hardiness range against that before treating it as long-lived ground.
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.
What Else to Consider for Blue Vervain in Washington
Zone compatibility tells you about winter cold survival — 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 blue vervain — is covered on the Washington growing guide.
Where in Washington Blue Vervain Is Zone-Hardy
Blue Vervain is rated for USDA zones 3–8. 26 of Washington’s 39 counties fall inside that band. The coldest that does is Ferry County at zone 6a. 13 counties sit above its zone 8 ceiling, where the limit is too little winter chill rather than too much cold. Where you are in Washington decides this one.
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 blue vervain 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". Blue Vervain’s zone 3–8 band: USDA PLANTS / Growable Ground plant database. A parcel report resolves your address’s own zone and frost dates rather than its county’s.
Pollinator + Wildlife Value
Blue Vervain draws honeybees, native bees, butterflies, and hummingbirds (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, blue vervain 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.
Washington Cooperative Extension
For Washington-specific cultivar recommendations, planting calendars, and pest pressure for blue vervain, the canonical source is WSU Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Blue Vervain native to Washington?
Yes — the USDA PLANTS Database (accessed 2026-07-01) documents Blue Vervain as native to Washington. Planting it supports the pollinators and wildlife that evolved alongside it.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing Blue Vervain in Washington
When can I plant Blue Vervain 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). No sourced winter-hardiness floor is on record for Blue Vervain, so this page does not state whether it overwinters in Washington and publishes no fall establishment date for it — check its hardiness range against your own zone before treating it as a permanent planting.
What hardiness zone is Blue Vervain grown in across Washington?
Washington spans USDA hardiness zones 4a-9b (USDA ARS PHZM 2023). Blue Vervain carries a range of zones 3-8, 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). Blue Vervain 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 Blue Vervain native to Washington?
Yes — the USDA PLANTS Database (accessed 2026-07-01) documents Blue Vervain as native to Washington. Planting it supports the pollinators and wildlife that evolved alongside it.
Will Blue Vervain actually grow on my specific land in Washington?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores blue vervain against your address's exact 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 blue vervain against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Washington blue vervain 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 blue vervain average
Explore More
Growing guides for blue vervain
Explore Washington county by county
Washington carries 39 counties with their own USDA zone — a sample of the growing pages for blue vervain there:
Where else blue vervain grows
Blue Vervain'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 1,038 plants — a rotating sample of the rest of the shelf.
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