Generally — Most Areas
black seed (zones 5-10) suits most of Washington (4a-9b) — zones 5-9 are in range, and the rest of the state is the exception.
Your yard isn't the whole zone.
Black Seed 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 black seed against your land's actual frost dates, sun, and soil.
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Zone Comparison
Black Seed Needs
- USDA Zones: 5-10
- Frost-Free Days: 90+
- Sun: Full Sun
- Mature size: 1.3 ft tall
- Picking window: ~21 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 5-10)
Preferred Soil pH
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Black Seed 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
Black Seed is direct-sown where it grows rather than started under cover, so there is no seed-tray head start to bank — Washington's dates above are the whole calendar for it. That makes the last-freeze date the binding constraint, and a warmer pocket of your own yard is worth more to this crop than it is to a transplanted one.
Days to maturity vs. the window
At 100 days to maturity (USDA PLANTS Database), counting from the last hard freeze it ripens with 92 days to spare even in Washington's tightest freeze scenario — room for a later start or a second sowing.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: USDA PLANTS Database. 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 black seed survives winter in part of Washington, not across all of it. Whether the season is long enough — and warm enough — is a different question.
Frost-free days
Black Seed wants 90+ 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
Black Seed needs ~1500 GDD (base 50°F) to ripen. The state median runs ~1740 GDD (from PRISM 1991-2020 climate normals), so Washington sits right at the threshold — pay attention to siting and microclimate.
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
Black Seed likes near-neutral soil (pH 5.5-8). 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 7.5 — 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, raised beds or amendment with compost solve it.
Plant pH and drainage requirements from USDA PLANTS Database. Washington soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Black Seed in Washington — Quick Answer
- Verdict: Generally — Most Areas
- Plant Zones: 5-10 (USDA PLANTS Database)
- State Zones: 4a-9b (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Mar 16 - Apr 15 to Oct 24 - Nov 18 (NOAA Regional Climate Centers ACIS, 1991-2020)
- Days to Maturity: 100 days
What Else to Consider for Black Seed 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 black seed — is covered on the Washington growing guide.
Timing shifts within Washington
Black Seed needs about 90 days of frost-free season to complete its cycle. Even Whatcom County — Washington’s shortest season at 131 frost-free days — clears that by 41 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 black seed about 118 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"). Black Seed's 90-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
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 black seed (USDA PHZM 2023):
Pollinator + Wildlife Value
Black Seed draws honeybees and native bees (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, black seed 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 black seed, the canonical source is WSU Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Black Seed native to Washington?
No — the USDA PLANTS Database lists Black Seed as introduced rather than native in the Lower 48, so it is not part of Washington's native flora. It grows here as a garden plant; pairing it with a few Washington natives keeps local pollinators fed too.
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 Black Seed in Washington
When can I plant Black Seed 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 Black Seed mature before first frost in Washington?
Yes — Black Seed matures in 100 days (USDA PLANTS Database), and Washington's dependable hard-freeze-free window runs 192 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 92 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 Black Seed grown in across Washington?
Washington spans USDA hardiness zones 4a-9b (USDA ARS PHZM 2023). Black Seed carries a range of zones 5-10, 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). Black Seed needs 90+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Black Seed native to Washington?
No — the USDA PLANTS Database lists Black Seed as introduced rather than native in the Lower 48, so it is not part of Washington's native flora. It grows here as a garden plant; pairing it with a few Washington natives keeps local pollinators fed too.
How should I amend the soil for Black Seed in Washington?
Black Seed prefers pH 5.5-8 and well (dry spells) drainage (Growable Ground Plant Database). 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 Black Seed actually grow on my specific land in Washington?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores black seed 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 black seed against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Washington black seed averages can't show:
We read public map data around Washington — soil, climate, flood, and parcel records. How we handle your address.
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