Soil Basics: The Dirt on Dirt

The health of garden plants depends on the soils composition.  Most soils are a combination of three particles: clay, sand, and silt.  The particle type that dominates determines many of the properties of your soil.

Soil Types

  • Sand

    • Contains few nutrients

    • Because of its large particle size, it has lots of air space, drains quickly, and heats up fast.

  • Clay

    • Naturally high in nutrients

    • Because of its small particle size, it has little air space, drains slowly, and is slow to warm up in spring.

  • Silt

    • Holds some nutrients

    • Because of its medium particle size, it holds some water (but not too much), and heats up fast in the spring (but not too fast).

For most plants, the ideal mixture is approximately:

  • 40% sand

  • 40% silt

  • 20% clay

This combination is called loam.  Soils that contain a majority of one of these particles provides a challenge for the gardener.

Adding organic matter, such as decayed plants and animals, helps soil particles bind together and improve the structure of sandy and clay soils.  Organic matter added to the soil will also encourage soil organisms (earthworms, beetles, etc) to tunnel through the soil, opening up space for air, water, and roots to pass through easily.

Suburban Soil of Fort Bend

Development over the years in the creation of residential subdivisions has greatly impacted the native soil.  Filler "trash" clay is commonly added on top of the native soil to raise the grade above street level. In these situations homeowners may find that they only have one or two inches of topsoil and while beneath that can be anything (including boards, wires, trash, etc).  So expect to find heavy clay and slightly alkaline soil when you begin to prep your gardens.

To improve your soil texture and structure, Texas A&M recommends you till three inches of expanded shale into the native soil.  Then till three inches of aged, plant-derived compost into the soil/expanded shale mixture.

Written by Kelli Bonnickson | Edited by Sebastien Serimontrikul