San Juan County, in Washington, sits in USDA hardiness zone 9a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Well-matched crops include artichoke, fig, california poppy, and cabbage, and the gap between "grows in the area" and "grows in your yard" is closed by soil, sun, and drainage.
San Juan County lies within the Puget Sound Lowlands and the Pacific Northwest — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
San Juan County holds more than one microclimate.
Soils and elevations shift across San Juan County, so your frost dates and drainage aren't the county average. Enter your address and we'll score 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around San Juan County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
San Juan County — the short answer
San Juan County, Washington: USDA zone 9a, about 300 days between hard freezes, across 111K acres.
- USDA zone
- 9a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Feb 9
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Dec 6
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~300
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 111K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 28°F normals: light frosts run a few weeks past them, and tender transplants usually wait 2–3 weeks after the last hard freeze.
Hardiness Zone Range
Zone 9a is San Juan County's average, not your lot's — a low corner or a tree line moves it. Against San Juan County's 300-day season, see what your own ground reads.
Heat in San Juan County
Across a year, San Juan County accumulates about 1,328 growing degree days above 50°F, about 385 fewer than the middle Washington county — ahead of 12 of Washington’s 39 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in San Juan County
Across San Juan County, the ground is predominantly Inceptisols, where Cady, Mitchellbay, and Doebay are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 5.1–5.7, strongly acidic. Rainfall drains through hydrologic group C/D soils.
Soil order
Inceptisols
Drainage
Well drained
Prime farmland
16%
Hydric soils
14%
Soil still varies lot by lot — soil types explained.
How the ground varies across San Juan County
The USDA soil survey maps 45% of San Juan County as well drained — but another 52% drains differently: 22% somewhat poorly drained, 18% moderately well drained.
Cady is the most extensive named soil at 19% of mapped acres, then Mitchellbay (12%) and Doebay (11%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in San Juan County
Each reading below is measured for San Juan County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across San Juan County are well drained, in hydrologic group C/D — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across San Juan County runs about pH 5.1–5.7, on the acidic side.
Blueberries, potatoes, and rhododendrons thrive in it, but most vegetables start locking out nutrients below about pH 6.0 and grow pale and stunted no matter how much you feed them.
A measured lime application raises pH for the crops that need it — but test first, because the right rate depends on your own soil, not the county average.
USDA NRCS SSURGO
Season length
MeasuredSan Juan County runs about 300 days between hard freezes — close to year-round growing.
Frost is rarely the limit here; winter plantings are as real as summer ones, and the harder question is which crops shrug off the summer heat.
Grow cool-season crops through the mild winter, and choose heat-tolerant varieties for the summer beds.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredSan Juan County sits in USDA hardiness zone 9a.
The zone sets which perennials, shrubs, and fruit trees live through an average winter here — a plant rated for a colder zone is a safe bet, one rated warmer needs winter protection or gets treated as an annual.
Match perennials and fruit to the zone before you buy, so nothing you plant is a gamble against the cold.
USDA PHZM 2023
The kind of country San Juan County is in
San Juan County sits in the Puget Lowland — EPA Level III, inside the wider Marine West Coast Forest. One consistent ecological setting across the whole county.
What Grows in San Juan County
We scored all 1,086 plants against San Juan County's own USDA zone 9a and its own 300-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's Washington profile.
Is it too late to plant in San Juan County?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Jan 12; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Feb 9 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Dec 6 — long-season crops need about 90 days of runway, quick greens only 30. With almost year-round growing weather, timing is about heat and rainfall more than frost — some bench is always in play.
Documented around San Juan County
- monarch butterfly1 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in San Juan County
USGS estimates 5,449 lb of Glyphosate on San Juan County farmland in 2019, its largest by weight, ahead of Bromoxynil (856 lb) and 2,4-d (509 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across San Juan County — and how to grow with it.
We checked the federal record across San Juan County — 79 documented sites across 4 of the 9 source types we track.
The most significant on record: 7 brownfield sites. Former commercial or industrial land where legacy contamination may persist.
The federal record across San Juan County is a modest one — a typical footprint for a growing area. Nothing here calls for alarm; it's worth knowing which recorded sites sit closest to where you grow, and each one on the map carries its type and location. If one turns out to be a near neighbor, a one-time soil test settles the question.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near San Juan County
Closest first, across San Juan County. Listing isn't leaking, and distance isn't exposure.
- PETRO SAN JUANUnderground Storage Tanks · 2.7 mi
- FRIDAY HARBOR TOWN OFPFAS · 3.3 mi
- FEDEX GROUND SAN JEAN ISLANDSBrownfields · 3.4 mi
- W A ROULEAU & SON INCUnderground Storage Tanks · 3.6 mi
- AERONAUTICAL SERVICES INCUnderground Storage Tanks · 3.7 mi
- ORCAS POWER AND LIGHT COMPANYUnderground Storage Tanks · 3.9 mi
- SAN JUAN COUNTY FIRE PROTECTION DISTRICT 3Brownfields · 3.9 mi
- SAN JUAN COUNTYUnderground Storage Tanks · 3.9 mi
- WA AGR M FRIDAY HARBOR 1Brownfields · 3.9 mi
- ISLAND PETROLEUM SERVICESUnderground Storage Tanks · 4.0 mi
- SNUG HARBOR RESORTUnderground Storage Tanks · 4.1 mi
- NORTHWEST AUTOUnderground Storage Tanks · 4.3 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from San Juan County's center, not your beds. Run your own address for what's upwind of you specifically.
Environmental Intelligence
The counts behind that headline — every source type on the record near San Juan County.
Sources Checked
across San Juan County
Severity Distribution
across San Juan County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around San Juan County, Underground Storage Tanks runs higher than the national average — 54 sites across San Juan County. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in San Juan County
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,086 plant recommendations.
25+ data sources read at your address, not the San Juan County average
Your land is one point inside San Juan County
Everything above resolves to San Juan County as a whole — one PHZM band and one county frost record, read across 111K acres. Your parcel is one point inside that footprint. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at county scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better county average.
Your Lot vs the San Juan County Average
San Juan County Average
- ●USDA Zones 9a, averaged across San Juan County
- ●One soil character for all of San Juan County
- ●Frost dates read at San Juan County's scale: Feb 9 to Dec 6
YOUR Parcel
- ✓Your exact zone, not San Juan County's 9a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in San Juan County
Pull a site-specific report for your exact address in San Juan County, Washington — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that San Juan County averages can't show:
We read public map data around San Juan County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the San Juan County average
How we know this about San Juan County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where San Juan County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about San Juan County
When does frost risk typically end in San Juan County?
The last hard freeze (28°F) in San Juan County typically lands around Feb 9, per NOAA 1991–2020 climate normals — earlier than the light-frost dates most charts quote. That marks the hard freeze, not the last light frost — lighter frosts keep biting past it, which is why tender transplants here wait until about Mar 2.
How long is the growing season in San Juan County?
Measured between 28°F hard freezes, San Juan County sees about 300 frost-free days — roughly Feb 9 through Dec 6, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Mar 2 to Nov 22, about 265 days.
Is the soil safe to grow vegetables in San Juan County?
The federal record around San Juan County shows 79 documented sites, mostly Underground Storage Tanks entries (54), the nearest Underground Storage Tanks record about 2.7 miles out — a typical footprint for a growing area, and proximity to a documented site is information, not a diagnosis of any one yard. It's worth seeing which recorded sites sit closest to where you grow, and testing the soil before new food beds near any of them.
Everything above is measured at San Juan County's scale — its 9a band and its 300-day season. Your yard writes its own version of San Juan County's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads Washington's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at San Juan County’s own scale
9 of the readings below were taken at San Juan County's own scale — its own ~300-day span between 28°F freezes, the 3 most extensive soil series mapped here and 79 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- San Juan County's own USDA hardiness band, zones 9aUSDA PHZM 2023
- San Juan County's own 28°F hard-freeze dates and its ~300-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in San Juan CountyUSDA NRCS SSURGO
- 79 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 2.7 miles outFederal environmental registers
- San Juan County's boundary and the 111,306 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 9a and a ~300-day seasonGrowable Ground crop-matching engine
- San Juan County sitting wholly inside the Puget LowlandUS EPA Level III Ecoregions
- Open occurrence records documented in San Juan County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto San Juan County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Washington grower plans around — written at state scale, so they stay on the state guidefrom Washington
What this page can’t tell you
- How the season shifts across San Juan County — the ~300 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among San Juan County's 111,306 acreswhy one lot differs from the next →
- Which of those 79 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over San Juan Countyread your own land →