Roberts County, in South Dakota, sits in USDA hardiness zone 4b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Growers here do well with cabbage, cranberry, turkish rocket, and collard greens — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
Roberts County lies within the Coteau des Prairies / Glacial Lakes (Northeastern SD) — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Roberts County holds more than one microclimate.
Soils and elevations shift across Roberts County, so your frost dates and drainage aren't the county average. 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 Roberts County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Roberts County — the short answer
Roberts County, South Dakota: USDA zone 4b, about 170 days between hard freezes, across 705K acres.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 24
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 11
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~170
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 705K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 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 Roberts County's average, not your lot's — a low corner or a tree line moves it. Against Roberts County's 170-day season, see what your own ground reads.
Heat in Roberts County
Across a year, Roberts County accumulates about 2,276 growing degree days above 50°F, about 150 fewer than the middle South Dakota county — ahead of 20 of South Dakota’s 66 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Roberts County
Across Roberts County, the ground is predominantly Mollisols, where Forman, Peever, and Heimdal are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 6.7–7.3, neutral. Rainfall drains through hydrologic group C soils.
Soil order
Mollisols
Drainage
Well drained
Prime farmland
48%
Hydric soils
17%
Soil still varies lot by lot — soil types explained.
How the ground varies across Roberts County
The USDA soil survey maps 67% of Roberts County as well drained — but another 30% drains differently: 8% poorly drained, 8% somewhat poorly drained.
Forman is the most extensive named soil at 18% of mapped acres, then Peever (15%) and Heimdal (7%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Roberts County
Each reading below is measured for Roberts County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Roberts County are well drained, in hydrologic group C — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Roberts County runs about pH 6.7–7.3, close to neutral.
This is the range most vegetables prefer — one correction you probably do not have to make, which is genuinely good news for a new bed.
Keep it there with compost rather than lime or sulfur, and only amend if your own soil test says otherwise.
USDA NRCS SSURGO
Wet ground
MeasuredAbout 17% of Roberts County is mapped as hydric — wetland — soil.
If your lot falls in one of those pockets, a standard in-ground bed will fight waterlogging all season, and roots that need air will struggle.
Check how your own ground drains before you dig; raised beds or moisture-loving plantings turn a wet corner from a problem into a niche.
USDA NRCS SSURGO
Season length
MeasuredRoberts County runs about 170 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
The kind of country Roberts County is in
Roberts County spans 2 EPA Level III ecoregions — Northern Glaciated Plains (95%) and Lake Agassiz Plain (5%). Which one your land falls in changes what grows wild there and how the ground behaves, and a county-wide answer cannot tell you which.
What Grows in Roberts County
We scored all 1,086 plants against Roberts County's own USDA zone 4b and its own 170-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's South Dakota profile.
Is it too late to plant in Roberts County?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around Mar 27; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 24 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 11 — long-season crops need about 90 days of runway, quick greens only 30. The tail of the season still works: sixty-day crops into late summer, quick greens after, garlic last of all.
Documented around Roberts County
- monarch butterfly2 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Roberts County
USGS estimates 295,611 lb of Glyphosate on Roberts County farmland in 2019, its largest by weight, ahead of Metolachlor & Metolachlor-s (108,511 lb) and Metolachlor-s (101,343 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Roberts County — and how to grow with it.
We checked the federal record across Roberts County — 404 documented sites across 6 of the 9 source types we track.
The most significant on record: 1 Superfund site (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
There's a meaningful federal record across Roberts County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Roberts County
Closest first, across Roberts County. Listing isn't leaking, and distance isn't exposure.
- 125N50W 8CCCC2 RNitrate · 0.7 mi
- 125N50W 8BBBA RNitrate · 0.7 mi
- 126N50W32CCCB R (SISSETON GW WELL RB-79D)Nitrate · 1.1 mi
- 125N51W12DCCC RNitrate · 2.0 mi
- 125N51W13ABBB2 RNitrate · 2.0 mi
- 125N51W13ABBB RNitrate · 2.0 mi
- 125N51W 1DCCC RNitrate · 2.1 mi
- 125N51W 1DBBB RNitrate · 2.2 mi
- 126N51W36DCCC RNitrate · 2.5 mi
- 125N51W12BBBB2 RNitrate · 2.5 mi
- 126N51W36ACDA RNitrate · 2.7 mi
- 126N51W36AACC RNitrate · 2.9 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Roberts County'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 Roberts County.
Total Sites
404
across Roberts County
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
across Roberts County
Severity Distribution
across Roberts County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Roberts County, Nitrate runs higher than the national average — 348 sites across Roberts County. 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 Roberts County
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 Roberts County average
Your land is one point inside Roberts County
Everything above resolves to Roberts County as a whole — one PHZM band and one county frost record, read across 705K 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 county 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 county average.
Your Lot vs the Roberts County Average
Roberts County Average
- ●USDA Zones 4b, averaged across Roberts County
- ●One soil character for all of Roberts County
- ●Frost dates read at Roberts County's scale: Apr 24 to Oct 11
YOUR Parcel
- ✓Your exact zone, not Roberts County's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Roberts County
Pull a site-specific report for your exact address in Roberts County, South Dakota — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Roberts County averages can't show:
We read public map data around Roberts County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Roberts County average
How we know this about Roberts County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Roberts County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Roberts County
When does frost risk typically end in Roberts County?
The last hard freeze (28°F) in Roberts County typically lands around Apr 24, 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 15.
How long is the growing season in Roberts County?
Measured between 28°F hard freezes, Roberts County sees about 170 frost-free days — roughly Apr 24 through Oct 11, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 15 to Sep 27, about 135 days.
Is the soil safe to grow vegetables in Roberts County?
The federal record around Roberts County is a meaningful one — 404 documented sites, mostly Nitrate entries (348), the nearest Nitrate record about 0.7 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.
Everything above is measured at Roberts County's scale — its 4b band and its 170-day season. Your yard writes its own version of Roberts County's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads South Dakota's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Roberts County’s own scale
9 of the readings below were taken at Roberts County's own scale — its own ~170-day span between 28°F freezes, the 3 most extensive soil series mapped here and 404 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Roberts County's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Roberts County's own 28°F hard-freeze dates and its ~170-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Roberts CountyUSDA NRCS SSURGO
- 404 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Nitrate record about 0.7 miles outFederal environmental registers
- Roberts County's boundary and the 704,675 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~170-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Roberts County spans, Northern Glaciated Plains the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Roberts County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Roberts County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every South Dakota grower plans around — written at state scale, so they stay on the state guidefrom South Dakota
What this page can’t tell you
- How the season shifts across Roberts County — the ~170 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Roberts County's 704,675 acreswhy one lot differs from the next →
- Which of those 404 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Roberts Countyread your own land →