Sandy Soil: What USDA Calls Sand

What is sandy soil?

A soil is sand, in USDA terms, when it is more than 85% sand and the percentage of silt plus 1.5 times the percentage of clay is less than 15.^[4] In plainer words, there is so little silt and clay that the soil behaves as loose, single grains.

In the Royal Horticultural Society’s gardening shorthand these are “light soils” that drain quickly after rain or watering, one of the six gardening types.^[1]

Sand holds the least plant-available water of any class, a median 0.84 inches per foot, carries just 0.90% organic matter, and water races through at 92 µm/s. 65.2% of sand acres fall in hydrologic soil group A, the fastest-infiltrating group. Sand warms early and is easy to dig, but it dries out fast and leaks nutrients.^[3][5][1]

Sand grain sizes

Sand is the coarsest of the three mineral separates, 0.05 to 2.0 mm across. The Soil Survey Manual splits that span into five grades by diameter.^[4]

Which grade dominates earns a modifier within the sand class: coarse sand is a total of 25% or more very coarse and coarse sand, fine sand is 50% or more fine sand (with fine exceeding very fine), and very fine sand is 50% or more very fine sand.^[4] Coarser grades drain and dry fastest; finer grades hold a little more water and are more erosion-prone.

Why water beads on dry sand

A thirsty sand that sheds water instead of soaking it up is water-repellent (hydrophobic). Soil particles pick up non-polar coatings and water beads on the surface instead of going in, then runs off or moves down in fingers that leave dry spots. Sandy soils are the most susceptible because of their low surface-area-to-volume ratio, as are soils high in organic matter and soils that swing between wet and very dry.^[6] Note that high organic matter is a cause here, not a cure.

The fixes are a soil wetting agent (surfactant) and not letting the soil bake bone-dry, which means watering more often in smaller amounts.^[6]

Wet sand

Sand usually drains fast, but not always. 22.8% of US sand acres are poorly or very poorly drained, and 25.4% carry a dual “/D” hydrologic rating, the flag for a water table near the surface. On a spot like that, drainage is the problem, not thirst, so a drought-tolerant plant list can steer you wrong; the is your sand actually wet? section walks through checking it. (52.0% of sand is, by contrast, excessively or somewhat excessively drained.)^[3][7][5]

Is sandy soil good for plants?

As it comes, sand is hard on most plants: it dries fast and holds few nutrients. Only 42% of rated sand acres reach land-capability Classes I–IV, and effectively none (0%) is prime farmland. With 0.90% organic matter and 0.84 inches of water per foot, there is plenty of room to improve it with compost, and plenty of drought-tolerant plants that thrive on it as-is. See plants for sandy soil and how to improve sandy soil.^[3][8][9][1]

Two more properties follow from its loose grains. Sand holds few nutrients because its cation exchange capacity is low: light-colored sands run about 3–5 meq/100 g, the bottom of the CEC ladder. And by erodibility, fine and very fine sands are highly erosive while medium and coarse sands are too large to move easily, a spread covered on the silt page. Color, meanwhile, says nothing about texture: sands run from pale to iron-stained red to dark where organic matter is high, as the clay page explains.^[10][11][12]

Where sandy soil is found in the US

Sand is most extensive in Florida, then Nebraska and Michigan. Its most widespread series is Valentine (Nebraska); Florida’s Lakeland and Myakka appear lower in the table.^[3]

Most widespread sand soil series

Frequently asked questions

What is sandy soil?

A soil that is more than 85% sand, so loose and single-grained that it drains and dries quickly and holds few nutrients.^[4][1]

Why does water bead on my sandy soil?

When sand dries out, non-polar coatings can make it water-repellent, so water beads and runs off. A wetting agent and more frequent, lighter watering restore it; letting it bake dry makes it worse.

Is sandy soil good for plants?

Only 42% of sand acres are cultivable cropland, and almost none is prime farmland, but compost helps, and drought-tolerant plants do well on it.^{[3][8][9][13]}

Where is sandy soil found?

Most of all in Florida, Nebraska and Michigan, in that order.^[3]