Building healthy and fertile soil is the basis of all organic gardening. By discovering the unique characteristics of your home garden, you can learn how to optimize the potentials of your soil, and grow the best herbs and vegetables that your garden can. You can start by understanding soil in general, and your own garden soil, in particular.

Related Topics: How to Build Healthy Soil

WHAT IS SOIL?
Soil is a living system – an ecosystem – composed of four elemental parts: minerals, gases, liquids, and organic life. Minerals are present in the form of soil particles, formed from the weathering of native rock and plant materials. Gases, particularly atmospheric gases, reside in the spaces between soil particles and provide essential nutrients, such as Nitrogen, to the plant roots. Liquids, mostly water and water-soluble minerals also are present in the pores between soil particles. These too transport critical minerals and nutrition directly to plant roots. Finally and perhaps most importantly, are the vast arrays of micro- and macro-organisms present in healthy soil. This group includes bacteria, fungi, nematodes, protozoa, arthropods, worms, and burrowing animals, which form the food chain that fuels all the major processing functions of garden soil.

SOIL TYPES
Different types of soil are classified by methods which essentially describe how they look and from which materials they were formed. Soil scientists use a classification system which divides all the various soils into 12 categories. Each category references the parent rock, the weathering processes involved, the presence of organic materials, and the saturation of the soil with water.

More practical for garden soil, is the simple classification system based on soil texture. This system depends on the relative amounts of each of the major kinds of soil particles; sand, silt, and clay.

SOIL LIFE
Garden soil is opaque to our eyes, but it is full of life. The micro-world hidden between soil particles is teeming with living things, from bacteria to earthworms. This world of prey and predators is a complex food chain that forms a critical web of life for your garden. They decompose organic matter; enhance soil structure; promote root growth; modulate populations of soil pathogens and plant diseases; and makes essential nutrients available to plants. Conventional farming and gardening practices tend to diminish the population of this essential life-force. Organic methods, on the other hand, enhance the soil to sustain healthy populations of soil micro-organisms.

ORGANIC MATTER & YOUR SOIL
The hallmark of healthy garden soil is its abundance of organic matter. Its importance cannot be overstated, since organic materials in your soil provide so much benefit. It is the primary fuel for the complex ecosystem of soil micro-organisms. It creates a more open and porous soil texture, maintaining good drainage and transport. It helps the soil retain water like a sponge and helps keep the soil moist and cool. And it mitigates excessive soil acidity and alkalinity.

TILTH: HEALTHY SOIL STRUCTURE
A soil that absorbs water quickly and drains well, and does not crust over or form clods is said to have good tilth. Tilth is the physical condition of garden soil as it relates to seedbed quality, easy seedling emergence, deep root penetration and ease in digging. Good tilth is dependent on aggregation – the process whereby individual soil particles are joined into clusters or “aggregates”. A well-aggregated soil allows for increased water entry, increased air flow, increased water-holding capacity, and resistance to soil erosion.

SOIL CHEMISTRY: pH
References to soil chemistry usually describe the alkalinity or acidity, or pH (potential Hydrogen), of soils. The full scale of pH ranges from zero to fourteen, with seven being neutral. Values below seven are considered acidic; number higher than seven are alkaline. In garden soil, the pH is important because the range in which plants can easily grow is limited. Too acidic or too alkali, and essential plant nutrients become chemically bonded to soil minerals and are not available for plant growth.

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