Humus refers to the decomposed vegetation that makes up about 10 percent of most garden soil. Adding humus, in the form of compost, to a garden increases its productivity and produces healthier plants. Humus-rich soil improves over time as more compost is added season after season, and plants decompose at the end of their life cycles.
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What is Humus?
Humus is inactive organic material, usually decomposed plants. Most soil has humus in varying amounts, which gives it the distinctive dark brown color. Humus is complex and is made up of a variety of substances that have decomposed to the point of being impossible to identify. Humus makes garden soil rich and provides nutrients to growing plants.
Composting to Make Humus Soil
Some gardeners make their own humus by composting organic, non-meat kitchen scraps with yard waste. A compost pile starts out as identifiable food particles such as vegetable tops, fruit peels or egg shells, leaves and dead plants, and over time breaks down into a rich, brown soil amendment. Applying it and working into garden soil provides extra nutrients for plants.
Rich humus is excellent at holding on to water and releasing it slowly to plant roots. Soil that lacks humus may either drain too quickly or not allow water to soak in at all. As water passes through the humus on its way to the plant, it has time to absorb nutrients.
Humus improves soil texture and planting conditions. Clay soil tends to clump, while sandy soil is too loose. Adding 1 to 2 inches of humus to the top of most soils and working it in will produce an improved planting medium that's texturally more sound, aiding in garden success. Improving soil texture balances its porousness and permeability, so it retains water and nutrients more readily and releases them to the plant roots, rather than sitting on top of soil or draining through too quickly.