Castlewood, South Dakota, sits in USDA hardiness zone 4a — 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 Castlewood, 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 Castlewood 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 Castlewood — soil, climate, flood, and parcel records. How we handle your address.
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Castlewood — the short answer
Castlewood, South Dakota: USDA zone 4a, about 160 days between hard freezes, across 736 acres of city.
- USDA zone
- 4a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 30
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 7
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~160
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 736 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 4a is Castlewood's average, not your lot's — a low corner or a tree line moves it. Against Castlewood's 160-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Castlewood
Each reading below is measured for Castlewood itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredCastlewood runs about 160 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
MeasuredCastlewood sits in USDA hardiness zone 4a.
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 Castlewood is in
Castlewood sits in the Northern Glaciated Plains — EPA Level III, inside the wider Great Plains. That is read at Castlewood's own centroid rather than borrowed from Hamlin County.
What Grows in Castlewood
Every plant below cleared Castlewood's own zone 4a and its 160-day season. Each card opens that plant's South Dakota profile. How we score.
Is it too late to plant in Castlewood?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Apr 2; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 30 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 7 — 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 Castlewood
Closest first, within ~10 miles of Castlewood. Listing isn't leaking, and distance isn't exposure.
- 115N52W35DABB2Nitrate · 250 ft
- 115N52W35DABBNitrate · 250 ft
- CASTLEWOOD FARMERS ELEVUnderground Storage Tanks · 250 ft
- ESTELLINE COMMUNITY OIL COUnderground Storage Tanks · 500 ft
- 115N52W35DBABNitrate · 700 ft
- THERESA MASONUnderground Storage Tanks · 1100 ft
- 115N52W35DBDBNitrate · 2100 ft
- CAT'S CORNER CONVENIENCEUnderground Storage Tanks · 2500 ft
- 115N52W27DDDDNitrate · 1.0 mi
- 114N51W 7BBBBNitrate · 1.7 mi
- 114N52W 4DDDD2Nitrate · 2.3 mi
- 114N52W10CCCCNitrate · 3.0 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Castlewood'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 Castlewood.
Total Sites
72
within ~10 miles of Castlewood
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
within ~10 miles of Castlewood
Severity Distribution
within ~10 miles of Castlewood
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Castlewood, Nitrate runs higher than the national average — 56 sites within ~10 miles of Castlewood. That's not a problem with your land — it's information about it.
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 Castlewood
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 Castlewood average
Your land is one point inside Castlewood
Everything above resolves to Castlewood as a whole — one PHZM band and one 28°F frost record, read across 736 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 city 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 Castlewood Average
Castlewood Average
- ●USDA Zones 4a, averaged across Castlewood
- ●One soil character for all of Castlewood
- ●Frost dates read at Castlewood's scale: Apr 30 to Oct 7
YOUR Parcel
- ✓Your exact zone, not Castlewood's 4a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Castlewood
Pull a site-specific report for your exact address in Castlewood, South Dakota — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Castlewood averages can't show:
We read public map data around Castlewood — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Castlewood average
How we know this about Castlewood
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this city’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Castlewood’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 city grain anywhere on this page — there is no city-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 Castlewood
When does frost risk typically end in Castlewood?
The last hard freeze (28°F) in Castlewood typically lands around Apr 30, 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 21.
When is the first frost in Castlewood?
The first hard freeze (28°F) in Castlewood typically arrives around Oct 7, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 23, so the watching starts about Sep 7 — about 160 days after the spring freeze cleared.
How long is the growing season in Castlewood?
Measured between 28°F hard freezes, Castlewood sees about 160 frost-free days — roughly Apr 30 through Oct 7, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 21 to Sep 23, about 125 days.
Is the soil safe to grow vegetables in Castlewood?
The federal record around Castlewood is a meaningful one — 72 documented sites, mostly Nitrate entries (56), the nearest Nitrate record under a tenth of a mile 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 Castlewood?
From about Sep 7 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 7 (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 7. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Castlewood's scale — its 4a band and its 160-day season. Your yard writes its own version of Castlewood'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 Castlewood’s own scale
6 of the readings below were taken at Castlewood's own scale — its own ~160-day season between 28°F freezes, the 736 acres it covers and 72 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Castlewood's own USDA hardiness band, zones 4aUSDA PHZM 2023
- Castlewood's own 28°F hard-freeze dates, about Apr 30 and Oct 7 and the ~160-day span between themNOAA 1991–2020 Climate Normals
- 72 documented contamination sites on the federal record near Castlewood, the closest Nitrate record under a tenth of a mile out from the town centreFederal environmental registers
- Castlewood's boundary and the 736 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4a and a ~160-day seasonGrowable Ground crop-matching engine
- The ecoregion at Castlewood's own centroid, the Northern Glaciated PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Castlewood's 736 acres read through its county's SSURGO summaryfrom Hamlin County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Hamlin 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 Hamlin County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Castlewood's 736 acreswhy one lot differs from the next →
- Which side of Castlewood you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 736 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Nitrate record under a tenth of a mile 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 Castlewood-wide figureread your own land →