Twin Brooks, South Dakota, sits in USDA hardiness zone 4b — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
Crops well matched to these conditions include cabbage, cranberry, turkish rocket, and collard greens — though what thrives on any one site still turns on its specific soil, sun, and drainage.
Even in Twin Brooks, 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 Twin Brooks 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 Twin Brooks — soil, climate, flood, and parcel records. How we handle your address.
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Twin Brooks — the short answer
Twin Brooks, South Dakota: USDA zone 4b, about 166 days between hard freezes, across 260 acres of town.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 27
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 10
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~166
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 260 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 Twin Brooks's average, not your lot's — a low corner or a tree line moves it. Against Twin Brooks's 166-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Twin Brooks
Each reading below is measured for Twin Brooks itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredTwin Brooks runs about 166 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
MeasuredTwin Brooks 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 Twin Brooks is in
Twin Brooks sits in the Northern Glaciated Plains — EPA Level III, inside the wider Great Plains. That is read at Twin Brooks's own centroid rather than borrowed from Grant County.
What Grows in Twin Brooks
Every plant below cleared Twin Brooks's own zone 4b and its 166-day season. Each card opens that plant's South Dakota profile. How we score.
Is it too late to plant in Twin Brooks?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Mar 30; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 27 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 10 — long-season crops need about 90 days of runway, quick greens only 30. As the window narrows, the plantings just get faster — fall brassicas, then greens, then garlic to finish.
What's on the federal record near Twin Brooks
Closest first, within ~10 miles of Twin Brooks. Listing isn't leaking, and distance isn't exposure.
- 120N50W14AABDNitrate · 950 ft
- 120N50W14AABCNitrate · 950 ft
- 120N50W13BBCANitrate · 1900 ft
- 120N50W11CDDDNitrate · 2000 ft
- 120N50W10DDDDNitrate · 0.9 mi
- 120N50W10DDDD2Nitrate · 0.9 mi
- 120N50W15AADDNitrate · 0.9 mi
- 120N50W36ADDDNitrate · 3.7 mi
- SD DEPT OF TRANSPORTATIONUnderground Storage Tanks · 5.1 mi
- BRIGHTMARK MILL VALLEY RNG, LLCBrownfields · 5.3 mi
- 121N50W24DDDDNitrate · 5.6 mi
- PAUL R. HICKSToxics Release Inventory · 5.8 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Twin Brooks'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 Twin Brooks.
Total Sites
76
within ~10 miles of Twin Brooks
Risk Level
Moderate
Highest-severity
4 Toxics Release Inventory facilities
Sources Checked
within ~10 miles of Twin Brooks
Severity Distribution
within ~10 miles of Twin Brooks
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Twin Brooks, Nitrate runs higher than the national average — 36 sites within ~10 miles of Twin Brooks. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around 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 Twin Brooks
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 Twin Brooks average
Your land is one point inside Twin Brooks
Everything above resolves to Twin Brooks as a whole — one PHZM band and one 28°F frost record, read across 260 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 Twin Brooks Average
Twin Brooks Average
- ●USDA Zones 4b, averaged across Twin Brooks
- ●One soil character for all of Twin Brooks
- ●Frost dates read at Twin Brooks's scale: Apr 27 to Oct 10
YOUR Parcel
- ✓Your exact zone, not Twin Brooks's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Twin Brooks
Pull a site-specific report for your exact address in Twin Brooks, South Dakota — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Twin Brooks averages can't show:
We read public map data around Twin Brooks — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Twin Brooks average
How we know this about Twin Brooks
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 Twin Brooks’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 Twin Brooks
When does frost risk typically end in Twin Brooks?
The last hard freeze (28°F) in Twin Brooks typically lands around Apr 27, 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 18.
When is the first frost in Twin Brooks?
The first hard freeze (28°F) in Twin Brooks typically arrives around Oct 10, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 26, so the watching starts about Sep 10 — about 166 days after the spring freeze cleared.
How long is the growing season in Twin Brooks?
Measured between 28°F hard freezes, Twin Brooks sees about 166 frost-free days — roughly Apr 27 through Oct 10, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 18 to Sep 26, about 131 days.
Is the soil safe to grow vegetables in Twin Brooks?
The federal record around Twin Brooks shows 76 documented sites, mostly Nitrate entries (36), the nearest Nitrate record about 0.2 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.
How do I protect my plants from frost in Twin Brooks?
From about Sep 10 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 10 (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 10. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Twin Brooks's scale — its 4b band and its 166-day season. Your yard writes its own version of Twin Brooks'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 Twin Brooks’s own scale
6 of the readings below were taken at Twin Brooks's own scale — its own ~166-day season between 28°F freezes, the 260 acres it covers and 76 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Twin Brooks's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Twin Brooks's own 28°F hard-freeze dates, about Apr 27 and Oct 10 and the ~166-day span between themNOAA 1991–2020 Climate Normals
- 76 documented contamination sites on the federal record near Twin Brooks, the closest Nitrate record about 0.2 miles out from the town centreFederal environmental registers
- Twin Brooks's boundary and the 260 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~166-day seasonGrowable Ground crop-matching engine
- The ecoregion at Twin Brooks's own centroid, the Northern Glaciated PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Twin Brooks's 260 acres read through its county's SSURGO summaryfrom Grant County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Grant 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 Grant County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Twin Brooks's 260 acreswhy one lot differs from the next →
- Which side of Twin Brooks you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 260 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Nitrate record about 0.2 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 Twin Brooks-wide figureread your own land →