Polk County Soil Data
Polk County, Iowa
USDA SSURGO / PHZMAvg pH
6.4
Texture
Silt loam
Drainage
Moderately well drained
Organic Matter
4.3%
Hydrologic Group
D
Data Story
About Soil in Polk County, Iowa
The State Standard for Soil
Polk County’s pH of 6.41 is almost identical to the Iowa state average of 6.43. This creates a perfectly balanced environment that supports a wide variety of Midwestern vegetation.
Silty Texture with Sandy Pockets
The soil contains 45.4% silt and nearly 30% sand, providing better drainage than many neighboring counties. This 29.6% sand content makes the ground easier to work for home gardeners.
High Organic Matter and Productivity
At 4.26%, the organic matter level is well above the state average of 3.81%. This high carbon content contributes to a solid soil score of 77.0, indicating prime agricultural land.
Moderate Hydrology in the Heartland
With an available water capacity of 0.192 in/in, the soil remains consistently moist. Though formal drainage classes are not listed, the sand-silt ratio suggests moderate water movement through the profile.
Abundant Growth in Zone 5b
Polk County sits in Zone 5b, perfect for everything from sunflowers to bell peppers. Start your urban or rural garden now to take advantage of this top-tier Iowa soil.
Soil Composition
Soil pH
Soil Series
Detailed soil series data not yet available for this county.
Hydrologic Group
Group D — High Runoff
Clay soils with very slow infiltration rates. Highest runoff potential. These soils have a permanent high water table or are shallow over impervious material.
Drainage Class
Moderately well drained
Water is removed somewhat slowly. May have a slowly permeable layer or seasonal water table.
Soil Profile
Dominant texture: Silt loam
Typical soil profile. Actual depths vary by location.
USDA Soil Orders
Soil Amendment Products
Browse products to improve your soil health and lawn performance.
Browse Soil AmendmentsFrequently Asked Questions
What type of soil does Polk County have?
Polk County's soil is classified as Silt loam. This indicates the relative proportions of sand, silt, and clay — 30% sand, 45% silt, and 23% clay. Loamy soils hold moisture well and support a wide range of plants.
Is Polk County's soil acidic or alkaline?
Polk County's soil has a pH of 6.4, which is moderately acidic. This range suits many crops and is common across much of the eastern US.
What is the drainage class for Polk County?
Polk County has a dominant drainage class of "Moderately well drained." Well-drained soils allow excess water to move through quickly, reducing waterlogging risk and supporting most field and garden crops.
What crops or plants grow well in Polk County's soil?
Based on Polk County's Silt loam texture, pH of 6.4, and Moderately well drained, the soil is well suited for vegetables, grains, and most field crops, row crops and vegetable gardens, most annual and perennial crops.
What USDA soil order is found in Polk County?
Polk County's dominant soil order is Inceptisols. Inceptisols are young soils with weak horizon development. They occur in a wide range of climates and parent materials.
Soil & Planting Advisory: Polk County
Soil Verdict
Polk County is in USDA hardiness zone 5b, a cold climate zone. where winter lows can reach -15°F. Freeze-thaw cycles are moderate; soil biology slows in winter but recovers reliably in spring, supporting a broad range of plants.
Planting Guidance
A wide plant palette is possible: deciduous trees, most shrubs, cool-season vegetables, and many perennials thrive here. Winter protection (mulch, burlap wraps) helps push the zone boundary for desired species. Always match plant selections to the specific microclimate of your property — low spots, slopes, and wind exposure can shift effective hardiness by half a zone.
Soil Implications
Moderate freeze-thaw cycles naturally aerate the soil but can also cause compaction in clay-heavy areas; annual core aeration is beneficial. Organic matter amendments decompose at a moderate pace — aim for 3-5% organic content for optimal fertility. When soil temperatures drop below freezing, microbial nitrogen cycling stops; spring fertilization is more effective than late-fall application.
Regional Context
Polk County closely matches the Iowa average hardiness conditions.
Planning your lawn? View lawn care data for Polk County on LawnByCounty.com →
Other Counties in Iowa
Soil data sourced from USDA SSURGO via Soil Data Access. Data is informational only and should not be used as a substitute for on-site soil testing. Contact your local NRCS office for site-specific soil information.