Lawn Care Guide for Sully County
Sully County, South Dakota
USDA SSURGO / PHZMData Story
About Lawn Care in Sully County, South Dakota
Moderate Maintenance Needs in Sully County
Sully County sits slightly above the national median with a lawn difficulty score of 55.3. This Hardiness Zone 4b region is also more favorable for turf than the South Dakota state average.
Balancing Water and Summer Growth
Annual precipitation averages 21.1 inches, requiring supplemental watering to meet the needs of a standard lawn. Growers navigate 30 extreme heat days and 2,802 growing degree days, which accelerates mowing frequency in early summer.
Nearly Perfect Soil pH Levels
At 6.92, the soil pH is almost perfectly centered in the ideal range for grass health. The soil contains 27.6% clay, providing decent moisture retention while 22.0% sand helps with structural stability.
Seventeen Weeks of Recent Drought
The county endured 17 weeks of drought over the past year, though current data shows 0% of the area is currently in a drought stage. To prepare for future dry spells, homeowners should maintain a taller grass height to shade the soil.
Focus on Fall Recovery
Target the period between May 8th and October 2nd for active growth. Fine fescue or Kentucky Bluegrass are excellent picks for this zone, especially when seeded in the late summer for optimal root establishment.
Lawn Difficulty Score
Top Grass Fit for Sully County
Excellent match
Jonathan Green Black Beauty Ultra
Jonathan Green
Top cultivar score: 92/100
Zone 4b vs Tall Fescue's 3–8 band.
Soil pH 6.91727589497739 vs Tall Fescue's 5.5–6.5 window.
Precipitation 21.07" + soil AWC vs Tall Fescue's 20–30" need.
Growing-degree-days + frost window vs a intermediate-difficulty establishment.
If you spend any time on lawn care forums, Reddit's r/lawncare, or YouTube lawn channels, one name comes up more than any other: Jonathan Green Black Beauty Ultra. It's practically a cult favorite, and the label, cultivar story, and long-running owner reports explain why. The secret is in the genetics.
In Sully County, USDA zone 4b, soil pH 6.9, Jonathan Green Black Beauty Ultra scores 92/100 — a strong zone match, adequate moisture, and a long enough establishment window.
Why we ruled these out
- Pennington Zenith Zoysia Grass Seed & Mulch — USDA zone 4b is below Pennington Zenith Zoysia Grass Seed & Mulch's effective range (5–10); not recommended for this county.
- Scotts Turf Builder Bermudagrass — USDA zone 4b is below Scotts Turf Builder Bermudagrass's effective range (6–11); not recommended for this county.
See our fit-score methodology for how survivability is determined.
Recommended Grasses
Blue Grama
Bouteloua gracilis
Climate Snapshot
Annual Precip
21.1"
Growing Degree Days
2,801.6
Base 50F
Last Spring Frost
05/08
First Fall Frost
10/02
Days Above 95F
30
Hardiness Zone
4b
Seeding Calendar — Zone 4B
Seasonal Lawn Care Checklist
Spring
- Apply pre-emergent herbicide when soil reaches 55F
- Overseed bare spots once frost risk passes
- Start irrigation if rainfall is below 1 inch/week
- Soil test every 2-3 years — adjust lime or sulfur as needed
Summer
- Mow at recommended height weekly
- Water deeply 1-2 times per week (1 inch total)
- Avoid fertilizing cool-season grasses in peak heat
- Scout for grubs and treat if >10 per sq ft
Fall
- Core aerate compacted areas
- Apply fall fertilizer (highest N application for cool-season)
- Continue mowing until growth stops
- Rake or mulch leaves to prevent smothering
Winter
- Avoid walking on frozen turf
- Service mower and sharpen blades
- Plan spring soil amendments based on fall test
- Keep lawn clear of debris
Watering Deficit Calculator
Monthly Deficit
2.1"
inches of water
Monthly Water
6,482
gallons
Estimated Monthly Cost
$51.85
at $0.008/gallon average
Estimates based on 21" annual precipitation and estimated evapotranspiration. Actual costs vary by local water rates.
Common Lawn Problems in Sully County
Drought Stress
With only 21 inches of annual rainfall, lawns in Sully County face significant drought stress. Consider drought-tolerant grass species and deep, infrequent watering.
Learn more about regional lawn challenges at The Lawn Report.
Lawn Care Advisory: Sully County
Lawn Verdict
Sully County is in USDA hardiness zone 4b, one of the coldest zones in the country. with winter lows reaching around -25.0°F. and 2,801.6 growing degree days, sufficient for most common turfgrasses. Moderate rainfall (21.1 inches) generally supports healthy lawns with minimal supplemental watering.
Seasonal Breakdown
Wait until after May 8 to seed or overseed; soil temperatures should consistently reach 50-55°F. Cool summers (July averages 74.4°F) reduce heat stress — maintain regular mowing and moderate watering. With 30.2 days above 90°F annually, warm-season grasses recover faster from summer stress than cool-season types. Aerate and overseed cool-season lawns by early fall, well before October 2; this is the best renovation window. Winters are harsh (January averages 16.9°F); avoid foot traffic on frozen turf and plan snow mold prevention.
Watering Guidance
Low annual precipitation (21.1 inches) makes irrigation essential for maintaining green turf through summer. Currently, 29.4% of the county is in abnormally dry according to the US Drought Monitor. Cool summers reduce water demand; overwatering is a bigger risk than drought stress.
Regional Context
Sully County is close to the South Dakota average temperature, USDA zone 4b helps guide grass selection compared to neighboring counties.
Want detailed soil composition, drainage classes, and soil series data? View soil details on SoilByCounty.com
Frequently Asked Questions
What USDA hardiness zone is Sully County in?
What is the best grass for Sully County?
How much rainfall does Sully County get?
What is the soil pH in Sully County?
Data sourced from USDA SSURGO, NOAA Climate Normals (1991-2020), USDA Plant Hardiness Zone Map, and US Drought Monitor. Lawn difficulty scores and grass recommendations are estimates for informational purposes only.
Explore more data for Sully County