Clay Loam Soil

What makes a soil clay loam

Clay loam is the middle rung between loam and clay. USDA’s Soil Survey Manual defines it as 27 to under 40% clay with more than 20 and up to 45% sand.^[1] On the triangle: 27 ≤ clay < 40 and 20 < sand ≤ 45. Silt fills the rest, so a clay loam carries somewhere between 15 and 53% silt.

In the hand it is sticky and holds a shape. Worked between thumb and finger, moist clay loam pushes out a ribbon one to two inches long that feels about equally gritty and smooth.^[2] The ribbon test walks through it step by step.

Clay loam vs loam and clay

Clay content is the main difference between the three, and it shows in the survey. Water moves through clay loam topsoils at a median 3 µm/s, about 3 times slower than through loam and about 14 times faster than through clay. It also holds more plant-available water per foot than clay itself (2.0 inches against 1.7).^[3]

Shrink-swell climbs the same ladder: a median linear extensibility of 1.5% for loam, 4.5% for clay loam (USDA’s moderate class) and 9.2% for clay.^[4] Moderate still means some shrinking and swelling as the soil dries and wets, though far less than in clay; the expansive soil checker reads every layer at an address.

Clay loam vs sandy soil

These sit far apart on the triangle, and the numbers show it. A clay loam topsoil holds about 2.4 times the water per foot that sand does (2.0 inches against 0.84), while water drains through sand about 31 times faster. Clay loam carries 2.0% organic matter to sand’s 0.90%, and 65.2% of sand sits in the free-draining hydrologic group A against 0.1% of clay loam.^[3][5]

Colorado State University puts the trade-off plainly: sandy soils drain quickly and don’t hold water and nutrients well, while clay holds both but drains slowly.^[6] Clay loam sits on the clay side of that line: Colorado State notes that a soil with only 20% clay behaves as a sticky, gummy clayey soil.^[2] How the three particles drive that is on sand, silt and clay, and pure sand has its own page.

What “heavy clay loam” means

“Heavy” is a gardener’s word, not a USDA class. It describes a clay loam near the top of its band, close to the 40% line where clay begins. Most mapped clay loam is not that heavy: the acre-weighted median clay content of clay loam topsoils is 31%, and the middle half falls between 30 and 33%.^[1][3]

Does clay loam drain well?

Most of it drains, slowly. 73.7% of clay loam acres are well drained, and 12.1% are poorly or very poorly drained.^[7] Saturated, the topsoil passes water at about 0.43 inches an hour, and 88.7% of the class sits in hydrologic groups C, D or C/D, where runoff is moderately high to high in a soaking rain.^[5]

Is clay loam good for gardens and crops?

Yes, with drainage in hand. USDA rates 57% of rated clay loam acres in Classes I–IV and 22% in the top two classes.^[8] 18.5% is mapped prime farmland and another 15.7% qualifies as prime only if it is drained, protected from flooding or irrigated.^[3][9]

The limits USDA records are mostly erosion (subclass e, 49% of rated acres), root-zone limits (s, 23%) and wetness (w, 16%). For a garden, the loosening work is the clay routine: compost worked through a new bed and a thin top-dressing on an established one, set out in compost for clay soil and how to amend clay soil. Or start from plants that already handle it, on plants for clay soil.^[3][8]

pH leans alkaline: 43.2% of clay loam acres are alkaline, 35.6% neutral and 21.2% acid in the survey. A soil test tells you which side your yard is on; the fixes are on how to raise or lower soil pH.^[3][10]

Erosion and clay loam

On Minnesota’s erodibility ranking, clay loam sits between loam and clay: less erodible than loam, more than clay.^[11] The whole ladder, silt at the top, is on the silt page.

Where clay loam is found in the US

Relative to each state’s own soil, clay loam is most common in Texas (16.5% of its classified acres), Iowa (15.5%), Montana (12.9%) and Minnesota (12.8%).^[3]

Most widespread clay loam soil series

Pullman, mapped most in Texas, is the most extensive clay loam series, followed by Canisteo (Iowa) and Webster (Iowa). Each links to its USDA series description in the table.^[3]

Digging in clay loam

Clay loam is one of OSHA’s own examples of cohesive Type A soil, the most stable of its excavation types. The label holds only when the deposit is strong enough and not fissured, disturbed or shaken by traffic, which a competent person checks at the trench.^[12] The soil types hub explains how that system differs from texture.

Frequently asked questions

What is clay loam?

A USDA texture class with 27–40% clay and 20–45% sand, between loam and clay. It holds water and nutrients well and drains more slowly than loam.^[1][3]

What is the difference between clay loam and clay?

Clay has 40% or more clay; clay loam stops below 40%. In the survey clay loam drains about 14 times faster and shrinks and swells far less (median LEP 4.5% against 9.2%).^[1][3][4]

Is clay loam good for gardening?

Yes, where it drains: 57% of its rated acres are cultivable, and 18.5% is prime farmland.^[3][8][9]

Does clay loam drain well?

73.7% of it is well drained, but water moves through it slowly (about 0.43 inches an hour), so it runs off in heavy rain.^[3][7]

Is clay loam better than sandy soil?

For holding water and nutrients, yes: it holds about 2.4 times sand’s water per foot. Sand wins on drainage, passing water about 31 times faster.^[3]

Where is clay loam found?

Texas has the most, then Montana and Iowa. It makes up 16.5% of Texas’s classified soil.^[3]