Soil structure is one of the most important—and often overlooked—factors in successful gardening and landscaping. It describes how individual particles of sand, silt, and clay bind together into small clusters called aggregates, creating spaces that allow air, water, nutrients, and roots to move through the soil.

Good soil structure supports vigorous root development, efficient drainage, moisture retention, and beneficial microbial activity. Even nutrient-rich soil can struggle to support healthy plants if its structure is poor.

Why Soil Structure Matters for Plant Health

Root development: Healthy soil contains interconnected spaces that allow roots to grow deeper and spread outward. Compacted soil restricts root growth, limiting access to water and nutrients.
Water infiltration and drainage: Well-structured soil absorbs rainfall and irrigation water while allowing excess moisture to drain away. Poor structure can cause surface runoff, standing water, and waterlogged roots.
Oxygen availability: Roots need oxygen to function. Healthy soil contains both water-filled and air-filled pores. When soil becomes compacted or saturated, oxygen levels decline, stressing roots and increasing the risk of root disease.
Moisture retention: Good soil structure balances drainage with water storage. Smaller pores retain moisture for plants, while larger pores provide drainage and aeration.
Beneficial microorganisms: Bacteria, fungi, earthworms, and other soil organisms help decompose organic matter, recycle nutrients, and create stable soil aggregates.

Understanding Utah's Clay Soils

Much of the Salt Lake Valley contains soils with significant clay content. Clay particles are extremely small and can hold substantial amounts of water and nutrients. However, poorly structured clay soils often become dense, sticky when wet, and hard when dry.

Compaction, excessive irrigation, and low organic matter can make these conditions worse. Some valley soils also contain elevated sodium, which can cause clay particles to disperse, reducing drainage and damaging soil structure.

This is why I source approximately 95% of our topsoil from mountain areas, primarily in Wasatch and Summit counties. I seek out soils with lower pH, lower salinity, and minimal lakebed clay content. These characteristics help us produce a more workable, better-draining growing medium than many native valley soils.

Improving Soil Structure

Incorporate mature compost: Well-decomposed organic matter encourages microbial activity and helps soil particles form stable aggregates. It can improve both water retention in sandy soils and aeration in clay-rich soils.
Avoid working wet soil: Tilling, digging, or driving equipment across saturated soil destroys aggregates and creates compaction. Allow soil to dry to a workable moisture level before disturbing it.
Prevent overwatering: Excessive irrigation fills soil pores with water, displacing the oxygen roots need. Water deeply when appropriate, but allow the soil to drain between irrigation cycles.
Protect the soil surface: Mulch and living plant cover reduce erosion, moderate soil temperatures, and help preserve moisture and aggregate stability.

The Role of Quality Topsoil and Compost

A productive growing medium requires more than the right nutrients. It needs a balance of mineral particles, organic matter, moisture, and air.

At Millcreek Topsoil, our Premium Blend combines screened sandy loam with aged compost to provide a workable growing medium that supports root establishment, moisture management, and biological activity.

For gardens, lawns, trees, and landscape beds, a properly prepared soil environment provides the foundation for long-term plant health.

The Bottom Line: About 95% of what makes up a plant comes from carbon, hydrogen, and oxygen, which plants obtain primarily from air and water. Fertilizers provide essential nutrients, but they account for only about 5% of what makes a plant grow.

Healthy soil structure is critical to collect and retain these nutrients. Build the soil first, and your plants will benefit for years to come.