Soil Basics

Soil is a plant's primary source of water and nutrients. It also provides the physical anchor that enables plants to stand upright. Gardeners must have a thorough knowledge of their soils' characteristics in order to produce healthy plants.

Soil vs. Dirt

Soil

Consists of air, minerals, water and decay from plants/animals
Alive with organisms: worms, fungi, insects, bacteria
Supports plant life
Made of sand, silt, clay, and organic matter
Holds moisture and nutrients
Provides anchoring for plants

Dirt

Undesirable material out of place
Mostly sand, silt, clay; may contain rocks
Lacks minerals, nutrients, and living organisms
No topsoil, humus, worms, fungi
No texture or structure
Does not compact when wet → leads to runoff & erosion

To ensure your soil is favorable for growing plants,

test your soil to learn if nutrients and amendments are needed.

Soil Composition

50% Solids

Weathered geologic material
Minerals
Decayed plant/animal remains (organic matter)

50% Pore Space

Filled with air and water
IMPORTANT: Air and water cannot occupy the same space, when one increases, the other decreases
Overwatering = plant decline or death

Common Soil Types & Traits

Sand

Great drainage
Poor at holding nutrients

Holds nutrients well
Poor drainage

Clay

Silt

Erodes easily
Moved by wind (dust storms) & water (floods)

Loam

40% sand, 40% silt, 20% clay
Ideal for most plants

Soil Types in Tarrant County

Cross Timbers – Sandy loam
Grand Prairie – Clays, limestone, silty loam
Blackland Prairie – Dark black to light grey clays

Soil Care

Improving Soil

Compost

Add 2–3 inches
Aerates and loosens clay
Adds nutrients & organic matter to sandy soil

Expanded Shale

Contains many air spaces
Loosens tight clay and improves workability

Best clay amendment: Expanded shale + compost
(Recommended by Dr. Steve George, Texas A&M)

Soil pH Basics

pH affects nutrient availability and plant health.

General soil in Tarrant County is typically alkaline, with pH ranging between 7.5 and 8.1.

Examples:

Azaleas: acidic pH 5.0–5.5
Blueberries: acidic pH 4.3–5.5
Vegetables & most ornamentals: slightly acidic pH 6–6.8
Clematis: neutral to slightly acidic pH 6–7
Salvias: tolerate alkaline soil pH 6.1–7.8

Adjusting Soil pH

Changing a yard 's native soil pH is difficult, however, the following can be tried:
To LOWER pH (more acidic): Add sulfur
To RAISE pH (more alkaline): Add lime
Gypsum = natural calcium + sulfur
Helps break up clay, reduces compaction

Tip! It is useful to remember that native plants perform better with local soil conditions

Watering Essentials

Hydrophobic soil

Water repels instead of soaking in
Common in dry, compacted, or organic-matter-poor soils

Best Watering Methods

Cycle & Soak for lawns
Infrequent, deep, slow watering
Drip irrigation is better than spray (especially for gardens)

Importance of Mulch

Conserves moisture
Protects roots
Limits weed growth
Improves soil quality
Regulates soil temperature
Use shredded, native hardwood

Healthy Soil Care

Add organic matter regularly
Avoid overwatering
Protect soil with mulch
Select native/adapted plants
Reduce compaction
Maintain proper pH
Test your soil every 3 years
- Click here for soil testing in urban/suburban areas

Resources

Here are several research-based fact sheets that expand on the topics covered in the Soil Basics.

Soil Testing through Texas A&M: The Texas A&M AgriLife Extension Serice offers soil testing. at its Soil, Water and Forage Testing Laboratory. The laboratory provides soil nutrient, pH, salinity and soil textural analyses with a primary focus on maintaining or improving plant growth. These testing options are listed on the soil submittal forms set forth in this website.

Quick Facts: Soil Physical Properties Factsheet — Overview of soil physical traits (texture, structure, porosity, bulk density), and how they affect drainage, root growth, and soil health. Texas A&M AgriLife Extension Service

Easy Gardening: Soil Preparation: A practical guide to improving garden soil: how to handle sandy or clay soils, how to add organic matter (compost, manure), tilling, raised beds, and prepping soil before planting. Texas A&M AgriLife Extension Service