Fort Thompson, South Dakota, sits in USDA hardiness zone 4b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
On paper, cabbage, cranberry, turkish rocket, and collard greens all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Even in Fort Thompson, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single Fort Thompson lot. 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 Fort Thompson — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Fort Thompson — the short answer
Fort Thompson, South Dakota: USDA zone 4b, about 180 days between hard freezes, across 7K acres of town.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 21
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 18
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~180
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 7K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are this town’s own 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 4b is Fort Thompson's average, not your lot's — a low corner or a tree line moves it. Against Fort Thompson's 180-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Fort Thompson
Each reading below is measured for Fort Thompson itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredFort Thompson runs about 180 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredFort Thompson sits in USDA hardiness zone 4b.
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 Fort Thompson is in
Fort Thompson sits in the Northwestern Great Plains — EPA Level III, inside the wider Great Plains. That is read at Fort Thompson's own centroid rather than borrowed from Buffalo County.
What Grows in Fort Thompson
Every plant below cleared Fort Thompson's own zone 4b and its 180-day season. Each card opens that plant's South Dakota profile. How we score.
Is it too late to plant in Fort Thompson?
Too late for some crops, right on time for others — a growing season is a sequence, not a deadline. Cool-season crops can go in from around Mar 24; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 21 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 18 — long-season crops need about 90 days of runway, quick greens only 30. Late in the year the fall bench takes over — quick greens, radishes, and garlic that repays you next summer.
What's on the federal record near Fort Thompson
Closest first, within ~10 miles of Fort Thompson. Listing isn't leaking, and distance isn't exposure.
- SHELBY'S MINIMARTUnderground Storage Tanks · 1.8 mi
- USCOE- BIG BEND DAM PROJECTBrownfields · 1.9 mi
- INDIAN HEALTH SERIVE HEALTH CENTERUnderground Storage Tanks · 1.9 mi
- 107N72W23BBBCNitrate · 2.2 mi
- CROW CREEK FORMER MUFFLER FACTORYSuperfund · 2.4 mi
- 107N71W 6CADNitrate · 2.8 mi
- ARMY CORPS OF ENGR - BIG BEUnderground Storage Tanks · 2.8 mi
- 107N72W 9ADCCNitrate · 4.1 mi
- US ACOE: LAKE SHARPE PROJECTBrownfields · 4.6 mi
- HUNKPATI ROAD STOPUnderground Storage Tanks · 5.8 mi
- LYNN'S DAKOTA MARTUnderground Storage Tanks · 5.8 mi
- 106N71W20CBBC RNitrate · 6.0 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Fort Thompson'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 Fort Thompson.
Total Sites
47
within ~10 miles of Fort Thompson
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
within ~10 miles of Fort Thompson
Severity Distribution
within ~10 miles of Fort Thompson
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Fort Thompson, Nitrate runs higher than the national average — 32 sites within ~10 miles of Fort Thompson. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Fort Thompson
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 Fort Thompson average
Your land is one point inside Fort Thompson
Everything above resolves to Fort Thompson as a whole — one PHZM band and one 28°F frost record, read across 7K 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 town 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 local average.
Your Lot vs the Fort Thompson Average
Fort Thompson Average
- ●USDA Zones 4b, averaged across Fort Thompson
- ●One soil character for all of Fort Thompson
- ●Frost dates read at Fort Thompson's scale: Apr 21 to Oct 18
YOUR Parcel
- ✓Your exact zone, not Fort Thompson's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Fort Thompson
Pull a site-specific report for your exact address in Fort Thompson, South Dakota — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Fort Thompson averages can't show:
We read public map data around Fort Thompson — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Fort Thompson average
How we know this about Fort Thompson
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this town’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Fort Thompson’s own record; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at town grain anywhere on this page — there is no town-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about Fort Thompson
When does frost risk typically end in Fort Thompson?
The last hard freeze (28°F) in Fort Thompson typically lands around Apr 21, 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 May 12.
When is the first frost in Fort Thompson?
The first hard freeze (28°F) in Fort Thompson typically arrives around Oct 18, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 4, so the watching starts about Sep 18 — about 180 days after the spring freeze cleared.
How long is the growing season in Fort Thompson?
Measured between 28°F hard freezes, Fort Thompson sees about 180 frost-free days — roughly Apr 21 through Oct 18, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 12 to Oct 4, about 145 days.
Is the soil safe to grow vegetables in Fort Thompson?
The federal record around Fort Thompson is a meaningful one — 47 documented sites, mostly Nitrate entries (32), the nearest Underground Storage Tanks record about 1.8 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
How do I protect my plants from frost in Fort Thompson?
From about Sep 18 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Oct 18 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Oct 18. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Fort Thompson's scale — its 4b band and its 180-day season. Your yard writes its own version of Fort Thompson's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at Fort Thompson’s own scale
6 of the readings below were taken at Fort Thompson's own scale — its own ~180-day season between 28°F freezes, the 6,641 acres it covers and 47 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Fort Thompson's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Fort Thompson's own 28°F hard-freeze dates, about Apr 21 and Oct 18 and the ~180-day span between themNOAA 1991–2020 Climate Normals
- 47 documented contamination sites on the federal record near Fort Thompson, the closest Underground Storage Tanks record about 1.8 miles out from the town centreFederal environmental registers
- Fort Thompson's boundary and the 6,641 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~180-day seasonGrowable Ground crop-matching engine
- The ecoregion at Fort Thompson's own centroid, the Northwestern Great PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Fort Thompson's 6,641 acres read through its county's SSURGO summaryfrom Buffalo County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Buffalo County
- The growing challenges every South Dakota grower plans around — written at state scale, so they stay on the state guidefrom South Dakota
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Buffalo County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Fort Thompson's 6,641 acreswhy one lot differs from the next →
- Which side of Fort Thompson you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 6,641 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 1.8 miles out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any Fort Thompson-wide figureread your own land →
More in South Dakota
Wider growing context
What grows across South DakotaFort Thompson sits outside our named growing regions, so South Dakota as a whole is its closest context here.
Nearby growing guides