What Is Soil?

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Some plants thrive in sandy soil, and others need the rich depth of loamy conditions while still others flourish in damp, heavy, clay soil. The soil is the foundation of a garden; it supports the plants, gives the plants' roots something to hold onto and makes nutrients and water available to the plants. Soil is a combination of inorganic particles and organic materials. The inorganic part of soil comes from rocks and minerals, and the organic part is made of decomposed plant material. The type of soil any garden has depends on the size of the inorganic particles.


Knowing Your Garden's Soil

Getting to know the soil before choosing plants or planting them is the first step in growing a successful garden. Typical garden soil is a combination of clay particles, sand and silt. Clay particles are fine compared to sand particles, which are coarse. Silt has fine particles, but they are less fine than clay particles. When the ratio of clay, silt and sand particles is equal and the soil contains some broken down plant materials, the soil is loam.

Understanding the Types

  • Loam is ideal for most plants, including garden plants. It is rich, simple to work and drains well. It supports plants without suffocating the roots, getting easily waterlogged or draining too quickly.
  • Sandy soil has a significantly higher amount of sand particles than clay and loam particles. Sandy soil is problematic because it drains quickly. The nutrients plants need are washed out of sandy soil, and it dries out too quickly for many plants.
  • Clay soil poses the opposite problem of sandy soil: It holds too much water, which is trapped between clay's fine particles. Some plants suffocate in clay soil's wet environment.
  • Silty soil is typically high in nutrients. It also drains well despite the fine size of its particles.


Measuring Drainage Rate

How well the soil in a garden bed or landscape area drains depends on the structure of the soil. Before planting, you can do a simple test to see if you have fast-draining soil, average or well-draining soil, or slow-draining soil.

  1. Dig a 12-inch-deep hole.
  2. Fill the hole to its top with water. Wait for the water to drain from the hole.
  3. Refill the hole with water, determine how many inches deep the water is with a ruler or tape measure and set a timer for 15 minutes.
  4. Calculate how many inches the water dropped during the 15-minute interval by measuring the water's depth after that time period.
  5. Multiply that number by four. The result is the amount of water that will drain out of the hole in one hour.


Interpreting the Results

  • If the water drains out more than 6 inches per hour or faster, then the soil is fast-draining and suitable for plants that need dry soil.
  • Drainage of 1 to 6 inches per hour indicates average or well-draining soil, which is suitable for most plants.
  • Soil that drains less than 1 inch per hour indicates a drainage problem that will negatively affect most plants.

Understanding pH Level

The pH scale is used to measure the ratio of acidic to alkaline compounds in soil. The pH level affects how well plants can access the nutrients in soil. Acid is low on the pH scale while alkaline compounds are high on the scale. A pH of 7 is neutral because it falls right in the middle of the 0 to 14 scale. Most plants grow well in slightly acidic to neutral soil with a pH of 5.5 to 7.