Keystone, South Dakota, sits in USDA hardiness zone 5a — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Reliable performers under these conditions include cabbage, cranberry, lavender, and collard greens; what your own ground favors still comes down to its soil, sun, and drainage.
Even in Keystone, 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 Keystone 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 Keystone — soil, climate, flood, and parcel records. How we handle your address.
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Keystone — the short answer
Keystone, South Dakota: USDA zone 5a, about 154 days between hard freezes, across 2K acres of town.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 6
- 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
- ~154
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 2K 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 5a is Keystone's average, not your lot's — a low corner or a tree line moves it. Against Keystone's 154-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Keystone
Each reading below is measured for Keystone itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredKeystone runs about 154 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
MeasuredKeystone sits in USDA hardiness zone 5a.
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 Keystone is in
Keystone sits in the Middle Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Keystone's own centroid, and it is not what its county reads: Pennington County is mostly Northwestern Great Plains. The wider page above you is answering a different question about different ground.
What Grows in Keystone
Every plant below cleared Keystone's own zone 5a and its 154-day season. Each card opens that plant's South Dakota profile. How we score.
Is it too late to plant in Keystone?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Apr 8; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 6 (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. As the window narrows, the plantings just get faster — fall brassicas, then greens, then garlic to finish.
What's on the federal record near Keystone
Closest first, within ~10 miles of Keystone. Listing isn't leaking, and distance isn't exposure.
- Henry Tin LodeMining · 600 ft
- Henry TinMining · 1700 ft
- MINERS C-MARTUnderground Storage Tanks · 1900 ft
- Bullion Mine Pennington CountyMining · 2300 ft
- Peerless MineMining · 2400 ft
- Peerless ProspectMining · 2400 ft
- ELK HAVEN TRADING POSTUnderground Storage Tanks · 2600 ft
- RUSHMORE RESORT & CAMPGROUND INCUnderground Storage Tanks · 2600 ft
- Keystone DistrictMining · 0.5 mi
- 002S06E08CADANitrate · 0.5 mi
- RUSHMORE HELICOPTERS INCUnderground Storage Tanks · 0.5 mi
- TOWN OF KEYSTONEUnderground Storage Tanks · 0.5 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Keystone'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 Keystone.
Total Sites
199
within ~10 miles of Keystone
Risk Level
Elevated
Highest-severity
3 Toxics Release Inventory facilities
Sources Checked
within ~10 miles of Keystone
Severity Distribution
within ~10 miles of Keystone
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Keystone, two things run higher than the national average within ~10 miles of Keystone — Mining (84 sites) and Nitrate (78 sites). That's not a problem with your land — it's information about it.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Keystone
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 Keystone average
Your land is one point inside Keystone
Everything above resolves to Keystone as a whole — one PHZM band and one 28°F frost record, read across 2K 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 Keystone Average
Keystone Average
- ●USDA Zones 5a, averaged across Keystone
- ●One soil character for all of Keystone
- ●Frost dates read at Keystone's scale: May 6 to Oct 7
YOUR Parcel
- ✓Your exact zone, not Keystone's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Keystone
Pull a site-specific report for your exact address in Keystone, South Dakota — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Keystone averages can't show:
We read public map data around Keystone — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Keystone average
How we know this about Keystone
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 Keystone’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 Keystone
When does frost risk typically end in Keystone?
The last hard freeze (28°F) in Keystone typically lands around May 6, 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 27.
When is the first frost in Keystone?
The first hard freeze (28°F) in Keystone 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 154 days after the spring freeze cleared.
How long is the growing season in Keystone?
Measured between 28°F hard freezes, Keystone sees about 154 frost-free days — roughly May 6 through Oct 7, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 27 to Sep 23, about 119 days.
Is the soil safe to grow vegetables in Keystone?
The federal record around Keystone is a meaningful one — 199 documented sites, mostly Mining entries (84), the nearest Mining record about 0.1 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 Keystone?
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 Keystone's scale — its 5a band and its 154-day season. Your yard writes its own version of Keystone'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 Keystone’s own scale
6 of the readings below were taken at Keystone's own scale — its own ~154-day season between 28°F freezes, the 1,921 acres it covers and 199 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Keystone's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Keystone's own 28°F hard-freeze dates, about May 6 and Oct 7 and the ~154-day span between themNOAA 1991–2020 Climate Normals
- 199 documented contamination sites on the federal record near Keystone, the closest Mining record about 0.1 miles out from the town centreFederal environmental registers
- Keystone's boundary and the 1,921 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~154-day seasonGrowable Ground crop-matching engine
- Keystone sits in the Middle Rockies — not the ecoregion its county mostly readsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Keystone's 1,921 acres read through its county's SSURGO summaryfrom Pennington County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Pennington 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 Pennington County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Keystone's 1,921 acreswhy one lot differs from the next →
- Which side of Keystone you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 1,921 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Mining record about 0.1 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 Keystone-wide figureread your own land →
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