The Puget Sound Lowlands spans USDA hardiness zones 8a-9a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
The maritime lowland ringing Puget Sound — EPA's Puget Lowland ecoregion across Island, Kitsap, Mason, San Juan, and Thurston counties — where mild marine winters hold USDA zones 8a-9a and a long 227-to-300-day frost-free season. On paper, kale, potato, garlic, and western red cedar all suit these conditions — on the ground, soil, sun, and drainage make the final call.
The Puget Sound Lowlands spans Washington.
Your yard isn't all of the Puget Sound Lowlands.
The Puget Sound Lowlands spans USDA zones 8a-9a, but your parcel sits in exactly one — and slope, tree cover, and low spots nudge it further. 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 Puget Sound Lowlands — soil, climate, flood, and parcel records. How we handle your address.
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The Puget Sound Lowlands — the short answer
The Puget Sound Lowlands: USDA zones 8a-9a, 227–300 frost-free days depending where in it you stand, in Washington.
- USDA zones
- 8a-9a
- USDA PHZM 2023, aggregated over the footprint
- Shortest season here
- 227 days
- NOAA Regional Climate Centers ACIS, 1991-2020 — Thurston County
- Counties
- 5
- US Census TIGER/Line 2025
- Region type
- County cluster
- Growable Ground growing-region registry
Region boundary: Growable Ground growing-region registry — curated county clusters, EPA Level III ecoregions, and town clusters drawn finer than any county. The season figure is this region's own record, measured across its 5 member counties, not a state or national average.
Hardiness Zone Range
The Puget Sound Lowlands is not one growing season
One answer for the Puget Sound Lowlands averages 5 counties whose growing seasons are 73 days apart — from 227 frost-free days in Thurston County to 300 in San Juan County. That is the same region, measured the same way, in the same years. Which end of it your land sits nearer decides what finishes before the first hard freeze.
The middle half of 5 counties runs 243–292 days, with a median of 285 days — a 73-day span end to end.
Measured across 5 member counties, each carrying its own 28°F normal. NOAA Regional Climate Centers ACIS, 1991-2020. A member with no own record is absent from the range rather than counted as zero — nothing here is interpolated to the region. Your own site sits somewhere inside this range; a parcel report resolves where.
Where the line runs inside the Puget Sound Lowlands
The middle half of the Puget Sound Lowlands runs 243–292 frost-free days, and 2 of its 5 counties sit outside that — 1 on the short side, 1 on the long. A regional planting date describes the middle well and the ends poorly, which is worth knowing before you follow one.
Under 243 frost-free days
1 county
- Thurston County · 227 days
The end of the region that sets the planting calendar — start seed indoors here and the season stretches to meet the crop.
243–292 frost-free days
3 counties
0 of 3 shown
The middle half of the region, and the part a single regional season describes well.
Over 292 frost-free days
1 county
- San Juan County · 300 days
Long enough for a second succession of a quick crop after the first comes out.
Each county is placed by its OWN 28°F frost-free normal (NOAA Regional Climate Centers ACIS, 1991-2020), the same figure its own guide page publishes. Elevation, slope and cold-air drainage move a site within its county as well — which is the part only your address resolves.
What Grows in the Puget Sound Lowlands
Plants matched to the Puget Sound Lowlands' USDA zones 8a-9a, ordered by how much hardiness margin each has across the region — the ones with room to spare at both ends of this band lead. Each links to its full growing profile.
Native Plants of the Puget Sound Lowlands
Plants the USDA PLANTS Database documents as native and present in this region’s state, kept only where the published hardiness range meets the Puget Sound Lowlands’s USDA zones 8a-9a — closest range match first. Presence is recorded by state, so a plant can be documented across the state and still be scarce in your corner of the region.
The ground across the Puget Sound Lowlands
The USDA soil survey maps this ground county by county. These are those records weighted by land area across five member counties — this region’s own profile, not a state figure.
The ground is predominantly Inceptisols, at 46% of mapped acres, followed by Andisols (25%), Entisols (13%) and Alfisols (7%). Eight soil orders appear somewhere inside the footprint, which is the honest reason a regional soil answer only goes so far. The most extensive named soils are Alderwood, Shelton, and Grove.
37% of those acres are moderately well drained, and another 26% well drained, 19% somewhat excessively drained. Topsoil pH runs 5.1–6.2 between the lowest and the highest county on record. 8% of the footprint is classed prime farmland.
Soil order
Inceptisols
Drainage
Moderately well drained
Topsoil pH
5.1–6.2
Hydric soils
7%
Soil changes across a driveway, so which of these your own ground sits on is a parcel question rather than a regional one. San Juan County holds the most wetland ground here, at 14% — soil types explained.
USDA NRCS SSURGO via Soil Data Access
What this means for growing in the Puget Sound Lowlands
The soil survey reads this ground county by county, and the readings above are those records summed across the Puget Sound Lowlands. Here is what they mean for a garden here — and the move an experienced grower makes about each one.
Drainage
From county records37% of the mapped acres across the Puget Sound Lowlands are moderately well drained — roughly the middle of the drainage range. That is area-weighted across all five of its mapped counties.
This is close to the middle most vegetables prefer: it holds enough water to carry a crop between rains without staying waterlogged. The catch is that a wet spring or a low corner can still tip it soggy.
Plant on the site as-is for most crops, but keep the lowest, slowest-draining beds for moisture-tolerant plantings.
USDA NRCS SSURGO
Surface pH
From county recordsTopsoil across the Puget Sound Lowlands runs pH 5.1–6.2 — acidic in all five of them.
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
Safe to Grow Here?
What the federal record shows across the Puget Sound Lowlands — and how to grow with it.
Across the Puget Sound Lowlands' 5 counties the federal record holds 2,744 documented sites, mostly Underground Storage Tanks (1,314), Nitrate (978) and Brownfields (330). The heaviest single county is Kitsap County, with 1,100.
That is a regional count, not a reading of any one lot — proximity to a documented site is information, not a diagnosis. Open the map outlined to the Puget Sound Lowlands to see which records sit where you actually grow.
Sources Checked
Summed across the 5 counties in the Puget Sound Lowlands
A note from Gnorman
What an experienced grower watches for around here
In and around the Puget Sound Lowlands, two things run higher than the national average across the 5 counties in the Puget Sound Lowlands — PFAS (40 sites) and Nitrate (978 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Your land is one point inside the Puget Sound Lowlands
Everything above resolves to the Puget Sound Lowlands as a whole — a footprint whose own counties record seasons 73 days apart, and hardiness across zones 8a-9a. Your parcel sits at one point in that range, not in the middle of it. 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 region 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 regional average.
Your Lot vs the Puget Sound Lowlands Average
Puget Sound Lowlands Average
- ●USDA Zones 8a-9a, averaged across Puget Sound Lowlands
- ●One soil character for all of Puget Sound Lowlands
- ●State-average frost dates
YOUR Parcel
- ✓Your exact zone, not Puget Sound Lowlands' 8a-9a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in the Puget Sound Lowlands
Pull a site-specific report for your exact address in the Puget Sound Lowlands — soil, sun, drainage, frost risk, contamination, and scored plant recommendations.
Three things about your lot that Puget Sound Lowlands averages can't show:
We read public map data around The Puget Sound Lowlands — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Puget Sound Lowlands average
How we know this about the Puget Sound Lowlands
The boundary: a cluster of neighboring counties. Growing regions have no official boundary, so this footprint is our published one, and every figure on this page was measured over the counties inside it rather than borrowed from the state around it.
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, aggregated across the footprint; the growing season from NOAA Regional Climate Centers ACIS 1991–2020 28°F normals, read at each member’s own record; boundaries from US Census TIGER/Line 2025; the contamination record from the federal sources named in that beat above; the soil from the USDA NRCS SSURGO survey, read at each member county’s own record and weighted to this footprint by land area. Where a member carries no record of its own, it is absent from the figure rather than filled in.
Common questions about the Puget Sound Lowlands
What hardiness zone is the Puget Sound Lowlands?
The Puget Sound Lowlands spans USDA hardiness zones 8a-9a, aggregated from the USDA Agricultural Research Service Plant Hardiness Zone Map 2023 across the region's counties. Zones reflect average annual extreme minimum temperatures from 1991–2020 data.
How long is the growing season in the Puget Sound Lowlands?
Measured between 28°F hard freezes, the Puget Sound Lowlands' counties mostly run 243 to 292 frost-free days, median 285 (NOAA Regional Climate Centers ACIS, 1991–2020, over 5 member counties). That 49-day spread is the honest read — no single season describes 5 counties, and each county guide below carries its own.
When does frost risk end in the Puget Sound Lowlands?
Across the Puget Sound Lowlands, the middle half of member counties see their last 28°F hard freeze between Feb 9 and Mar 17 (median Feb 15), and their first fall freeze between Nov 15 and Nov 27. Those are hard freezes, not the last light frost: tender transplants wait for about Mar 8, and elevation decides which end of a 36-day spread you garden in.
What grows well in the Puget Sound Lowlands?
The Puget Sound Lowlands' conditions suit plants such as Kale, Potato, Garlic, Western Red Cedar, Grape, Apple. What actually thrives on any one site still turns on its specific soil, sun, and drainage — we score each plant against the real conditions at your address.
How is the Puget Sound Lowlands defined?
The Puget Sound Lowlands is defined here as a curated cluster of 5 neighboring counties that share a growing character. Growing regions have no official boundary, so this footprint is our published one — every county in it is named on this page.
Which states does the Puget Sound Lowlands cover?
The Puget Sound Lowlands spans Washington. Each state's full growing guide is linked on this page.
What other growing regions cover the same states?
Pacific Northwest, Columbia Basin, Columbia Gorge, Inland Northwest (Northeast Washington), Olympic Peninsula, and Olympic Rain Shadow share at least one state with the Puget Sound Lowlands. Growing regions overlap and interlock — a single address can sit inside more than one, which is why the precise read is always the parcel, not the region.
What this page reads at the Puget Sound Lowlands’s own scale
6 of the readings below were taken at the Puget Sound Lowlands' own scale — the zone 8a-9a band across its footprint, a median 285-day season across its 5 counties and 2,744 documented federal contamination records across its 5 counties, 1,100 of them in Kitsap County alone; one is borrowed from a wider read, named and linked below.
Measured here
- The USDA hardiness band 8a-9a aggregated across all 5 counties in the footprintUSDA PHZM 2023
- The boundary itself — the 5 counties this region is curated fromGrowable Ground subregion registry
- The growing character that makes this region distinct from the states it crossesGrowable Ground subregion registry
- The 28°F season across the footprint — the middle half of its 5 counties run 243 to 292 frost-free days, median 285NOAA Regional Climate Centers ACIS, 1991-2020
- The federal contamination record over the whole footprint — 2,744 documented federal contamination records across its 5 counties, 1,100 of them in Kitsap County aloneEPA, USGS and USDA federal site records
- The soil order mix across the footprint — 46% Inceptisols, topsoil pH 5.1–6.2, area-weighted across its 5 mapped countiesUSDA NRCS SSURGO
Inherited from a wider read
- The candidate plant list — its state's curated sets, merged and filtered to zones 8a-9afrom Washington
What this page can’t tell you
- Which end of the 49-day range your ground sits at — 243 days at one extreme, 292 at the other, decided mostly by elevationfrost dates explained →
- Which of those soils your own ground sits on — the survey maps them county-wide, and they change across a drivewaysoil types explained →
- The soil pH, drainage, sun hours, and frost pockets on one specific lotwhy one lot differs from the next →
Explore the Puget Sound Lowlands
State growing guides
Counties in this region
Other growing regions across Washington
The maritime Northwest west of the Cascade crest — mild, wet winters and dry summers behind berries, tree fruit, and lush cool-season gardens. (Union of the west-side ecoregions.)
A dry basalt plateau of loess soils in the inland Northwest where irrigation turns arid ground into apple, cherry, hop, and wine-grape country.
A river canyon cut through the Cascades where wet marine air gives way to high desert in forty miles — pear, cherry, and apple orchards at the west end, vineyards and dryland ground at the east.
The coldest, most continental corner of Washington. Spokane sits at USDA zone 6b, and the Colville and Selkirk highlands of Ferry and Pend Oreille counties drop to 6a — two to three zones colder than the state's maritime west side. Frost-free windows run just 167 to 202 days here, so the growing calendar leans on cold-hardy varieties, a later last-frost start, and a shorter tomato-and-pepper season than anywhere else mapped in Washington. This is NOAA's Northeastern Washington climate division (#9) — hot, dry summers and cold-snap winters across Spokane, Colville, Republic, and Newport.
The Olympic Peninsula grows in a maritime world of its own. Cooled and watered by the open Pacific and the Strait of Juan de Fuca, its four counties — Clallam, Jefferson, Grays Harbor, and Mason — hold one of the widest rainfall gradients in the contiguous U.S.: from the Hoh and Quinault temperate rainforests (140+ inches a year) to the Sequim–Dungeness rain shadow near 16 inches that made the valley North America's lavender country. Long, mild, cloud-tempered seasons (USDA zones 8a–8b) favor cool-season crops — brassicas, alliums, salad greens, hardy berries, and cider apples — over heat-lovers, and frost timing swings sharply as you climb from tidewater toward the Olympic Mountains (which is why Jefferson County reads a full zone cooler and shorter-seasoned than its coastal neighbors). This page reads the peninsula's own counties, not a Pacific-Northwest-wide average, so the season and zone figures reflect the coast you're actually standing on.
Tucked in the Olympics' dry lee, Sequim and the island towns see a fraction of the rain that soaks the rest of western Washington — sunny, mild 8b-9a garden country where lavender thrives and irrigation, not drainage, is the summer question.