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Your Vegetable Garden Soil

Garden wisdom: “Don’t try to grow a 5 dollar plant in a 50 cent hole. For the best results, grow a 50 cent plant in a 5 dollar hole.”

Growing vegetables starts with the soil. Soil is a mix of fine rock particles, water, air, organic matter, microorganisms, and other animals including worms. Soil is formed by the action of the weather, water, and air on rocks which causes them to break down. Over thousands of years, the surface of rock becomes soft and decays to become soil.

Plants add value to the soil in two ways: by root action which further breaks down rock and soil particles, and, secondly, when plants die, they decay and form humus, an organic material that makes the soil more fertile. Soil provides plants with air, water, nutrients, and a place to grow.

The native soil in your garden is a mix of the rock below it and organic matter including decayed plants and animals, animal manure, and dead and decaying soil organisms. Soil varies from place to place. Silty soil is often found near the coast, lakes, and rivers. Sandy and clay soils are found both near and away from water. Alkaline soils are commonly found above limestone deposits, often in very dry climates.

clay sand silt loam soil

A soil textural triangle is used to determine soil textural class from the percentages of sand, silt, and clay in the soil.

Types of soil

Scientists have described many different soil textures, all a combination of differing proportions of sand, silt, clay, and humus. Several kinds of soil can exist in one backyard. Here are basic soil types and soil-related descriptions:

  • Clay soil is made up mostly of very small finely textured flat particles. Clay particles commonly pack together tightly like a stack of wet plates; they stick together. Clay soil is sticky when wet and hard and crusty when dry. Clay soil particles are so dense they make it difficult for oxygen to reach plant roots and water to drain away. Clay soil compacts easily and is slow to warm in spring.
  • Sandy soil is made up mostly of large, coarse particles. The space between sand particles is relatively large and porous. Sandy soil allows water and nutrients to drain away easily. When soil can’t hold water and nutrients, plants can’t thrive.
  • Silty soil is minute, smooth, and fine. Between your fingers, it feels much like flour. Silt particles under a microscope are irregular in shape. Mineral elements can adhere to silt unlike clay or sand particles. Silty soil tends to be fertile. As well, silt allows for soil oxygen to pass through. Silt usually doesn’t make up a very high proportion of any soil except where it is washed and deposited by water and combines with clay.
  • Humus rich soil. Humus is not a soil per se, but a description of the advanced decay of organic matter in soil. Humus is organic matter made up of decayed leaves, plant parts, and rotting soil microorganisms and animals. Humus might be described as gummy but not sticky like clay. Humus can fill the space between soil particles, coating sand, silt, and clay particles so that they cling together to form crumbs of soil. Humus binds soil moisture and minerals to soil crumbs making the moisture and minerals available to plant roots. Humus makes sandy soil heavier and clay soil lighter. Humus makes soil “friable,” meaning easy to work. Plants like to grow in friable soil.
  • Loam and sandy loam is the combination of a moderate amount of sand, some clay and silt, and humus. When sand, clay, and silt particles are present but no one is dominate and humus is present, the soil is called loam. Loam is warm, easy to work, and holds moderate amounts of moisture and nutrients. Loam is a good growing medium for plant roots and an outstanding vegetable garden soil. Slightly sandy or silty loam are the gold standard of garden soil.

Soil texture

The texture of soil helps to determine its fertility. Soil texture and fertility can be improved by the addition of humus and lesser decayed organic matter (as evidenced in loam). The more organic matter added to sand, silt, and clay the more improved the texture of the soil.

A very good soil mix

Here’s one formula for a very good soil mix:

  • About 40 to 45 percent inorganic rock materials—particles of sand, silt, and clay.
  • About 25 percent soil water.
  • About 25 percent soil air—a combination of oxygen and carbon dioxide.
  • About 5 to 10 percent humus—fully and partially decayed plant and animal remains. Humus binds sand, silt, and clay particles to make soil crumbs.

Related articles of interest:

How to Improve Clay Soil

Vegetable Plant Nutrients: Sources and Deficiencies

Soil Making The Kitchen Garden

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. has more than 10 million visitors each year.

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