What Are the Three Classes of Soil Texture?

Sandy Soil

• Sand is the largest of the three types of particles, with diameters between .4 and .01 inch and feels gritty when rubbed between your finger tips. It may also have various amounts of gravel mixed in. This texture has large spaces between the grains and holds water and nutrients poorly. It's ideal for some plants, however, especially those that need excellent drainage. Adding organic matter such as peat moss, well-rotted manure and compost is the best way to improve this soil. The organic material acts like a sponge, absorbing water and slowly releasing it along with nutrients absorbed from the manure or compost.

Silty Soil

• Silt feels smooth and silky to the touch and has fine particles, between .01 and .0001 inch diameter. Water clings to these tiny particles but is still available to roots when they need it, and the dissolved minerals also remain in the root zone instead of washing downward. The main disadvantage of silt is that it is easily compacted by the pressure of machines or constant walking.

Clay Soil

• Clay has the smallest particle size of all, less than .0001 inch diameter, and usually has a flattened, plate-like shape that tends to stack into impenetrable blocks. It feels sticky to the touch. Pore space is minimal, especially if the clay is compacted by pressure, and the water that is absorbed is held so tightly by surface tension that roots have difficulty absorbing all of it. Clay has other disadvantages also, including a tendency to crack when dry and to compact further if worked when wet. It drains poorly and warms up slowly in spring. However, nutrient holding ability is high and, if balanced by other factors, clay will help soils maintain an even moisture level. Improving clay soils means adding lots of organic matter. The end product of decay is humus, a sticky substance that binds clay particles together into larger grains, improving poor space. The undecayed fibers open up the soil and help it to drain.

Soil Combinations

• Most soil systems combine these three into 12 different categories, sandy clay, clay/sand, silty sand, sandy silt and so on. Soils are rarely made up of of only one texture. You can estimate the percentage of sand, silt and clay by rubbing it between your fingers. If it feels gritty, but is also sticky, you have a mixture of sand and clay. If it's gritty but also smooth and not sticky, you have a sandy silt or silty sand, depending on the proportions.