Yes — Strong Match
moonflower (zones 3-11) covers every zone Washington contains (4a-9b), so hardiness is not what limits it anywhere in the state.
Moonflower in Washington — the short answer
Moonflower in Washington: hardy in zones 3–11, full sun, against a state median of ~208 frost-free days.
- Plant zones
- 3-11
- 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
- Days to maturity
- 80 days
- Growable Ground Plant Database
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.
Moonflower 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 moonflower against your land's actual frost dates, sun, and soil.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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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 moonflower 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 moonflower (USDA PHZM 2023):
Zone Comparison
Moonflower Needs
- USDA Zones: 3-11
- Frost-Free Days: 30+
- Sun: Full Sun
- Mature size: 15 ft tall
- Picking window: ~90 days of harvest
- Drought tolerance: Medium
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 3-11)
Preferred Soil pH
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 Moonflower 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 moonflower goes out, not when it starts. It is sown under cover about 4 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.
Days to maturity vs. the window
At 80 days to maturity (Growable Ground Plant Database), counting from the last hard freeze it ripens with 112 days to spare even in Washington's tightest freeze scenario — room for a later start or a second sowing.
Timing tuned to sub-state frost dates — Whatcom County, not the statewide average.
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.
Growing Season Fit
The zone check says moonflower survives winter here. Whether the season is long enough — and warm enough — is a different question.
Frost-free days
Moonflower wants 30+ frost-free days; a typical Washington site sees ~208 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Moonflower needs ~1200 GDD (base 50°F) to ripen. The state median runs ~1740 GDD (from PRISM 1991-2020 climate normals), so Washington's typical season clears that easily.
GDD and chill-hour figures are computed from PRISM 1991-2020 monthly climate normals; frost-free days from NOAA Regional Climate Centers ACIS, 1991-2020. Each is the state median across its counties (P25/P75 span the within-state spread). Hardiness-zone range is USDA PHZM 2023.
Soil + Drainage Fit
Moonflower tolerates a wide pH range (pH 4.3-7.5) — 3.2 units, acid ground through alkaline — so soil acidity is rarely what limits it in Washington. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant. It will grow across that whole span, but it does best between pH 5 and 7 — worth knowing before you decide whether a Washington soil test result is a problem or just a number. Drainage requirement: poorly (saturated >50% of year). A soil-survey lookup (NRCS SSURGO) flags whether your specific site matches.
Your land, not the state average
Washington's soils run mostly silt loam, but SSURGO maps the series, texture, and drainage under your exact parcel. Moonflower needs about 7 inches of workable depth, so it is that horizon — not the surface — you are testing for. That map unit, not the state average, decides how moonflower performs.
Check your parcel → Source: USDA NRCS SSURGO.
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 Moonflower 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
Growing moonflower here specifically
Washington's soils run mostly silt loam (Mollisols), and whether that suits moonflower's pH 4.3–7.5 preference comes down to your exact parcel, not the statewide picture.
Pull your parcel's SSURGO map unit, test pH, and amend toward moonflower's 4.3–7.5 target before planting. How to handle it →
What to actually do about these — and the constraints that apply to every Washington grower, not just moonflower — is covered on the Washington growing guide.
Timing shifts within Washington
Washington isn't one climate. In Whatcom County, the last hard freeze (28°F) holds until about May 29 — roughly 54 days later than the recorded state median — so plant moonflower to your county's window, not the statewide date.
Moonflower needs about 30 days of frost-free season to complete its cycle. Even Whatcom County — Washington’s shortest season at 131 frost-free days — clears that by 101 days, so season length isn’t the constraint anywhere in Washington. What varies is your own parcel.
Across Washington’s 39 counties the frost-free season runs from 131 days in Whatcom County to 300 days in San Juan County — a spread of 169 days, which is why a single statewide planting date misleads. The median Washington county sees 208 frost-free days, leaving moonflower about 178 days of slack on a typical parcel — room for a second sowing where the season runs long.
County last-freeze dates and frost-free day counts: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F freeze (earlier than the folk 32°F "last frost"). Moonflower's 30-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Pollinator + Wildlife Value
Moonflower draws moths and hummingbirds (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, moonflower 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.
Good to Know Before You Plant Moonflower
Moonflower is listed as toxic to dogs, cats (seeds) at a mild level (ASPCA). Most listed plants only cause brief upset — a raised bed or a fenced corner usually keeps curious pets clear. Worth knowing for placement: in Washington this is a one-season plant and the first hard freeze (Oct 24 - Nov 18) takes it down, so the exposure above is a summer-long one rather than something standing in the bed all year.
Recommended Moonflower Varieties for Washington
Washington publishes no state variety trial for moonflower, so we won't invent a "best for Washington" list. Choose types rated to your USDA hardiness zone (4a-9b), and confirm winter survival and drainage against your own parcel.
Washington Cooperative Extension
For Washington-specific cultivar recommendations, planting calendars, and pest pressure for moonflower, the canonical source is WSU Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Moonflower native to Washington?
Moonflower is native to parts of the Lower 48, but the USDA PLANTS Database (accessed 2026-07-01) does not document a native range in Washington. It can still earn a place in a Washington garden — the zone comparison above tells you whether it will thrive.
Looking for plants that belong here? The Washington growing guide lists USDA-documented natives for the state.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing Moonflower in Washington
When can I plant Moonflower 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.
Can Moonflower mature before first frost in Washington?
Yes — Moonflower matures in 80 days (Growable Ground Plant Database), and Washington's dependable hard-freeze-free window runs 192 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 112 days of margin. Plant once the last hard freeze has passed — two to three weeks later for anything tender — and it ripens ahead of the first fall freeze.
What hardiness zone is Moonflower grown in across Washington?
Washington spans USDA hardiness zones 4a-9b (USDA ARS PHZM 2023). Moonflower carries a range of zones 3-11, 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). Moonflower needs 30+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date. In cooler counties like Whatcom, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Moonflower native to Washington?
Moonflower is native to parts of the Lower 48, but the USDA PLANTS Database (accessed 2026-07-01) does not document a native range in Washington. It can still earn a place in a Washington garden — the zone comparison above tells you whether it will thrive.
How should I amend the soil for Moonflower in Washington?
Moonflower tolerates pH 4.3-7.5 and poorly (saturated >50% of year) drainage (FAO ECOCROP). That is a 3.2-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a Washington site — amend for drainage and organic matter first.
Will Moonflower actually grow on my specific land in Washington?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores moonflower 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 moonflower against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Washington moonflower 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 moonflower average
Explore More
Growing guides for moonflower
Explore Washington county by county
Washington carries 39 counties with their own USDA zone — a sample of the growing pages for moonflower there:
Where else moonflower grows
Moonflower'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.
Analysis by the Growable Ground research team, grounded in USDA PLANTS, USDA NRCS SSURGO, NOAA Climate Normals (1991-2020), and named Cooperative Extension sources. How we know →
Cite this dataset
Kirchick, M. (2026). Growable Ground Plant Database [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21435643
Licensed CC BY-NC 4.0. DOI 10.5281/zenodo.21435643
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