What Is Humus Soil?

Humus is not a soil type but is in fact a mature compost, either made through a composting process or found in nature, such as the rich topsoil found in some forests. It is the most nutritious planting material and is used for planting as well as for treating soil. Depending on the type of soil garden plants are grown in, plants react in different ways. The 3 basic types of soil are clay, sandy, and loamy soils. Clay is characterized by a dense, slippery texture, and sandy soils tend to be made up of large particles, primarily of silicate materials. Loamy soils are generally dark in color and composed of organic materials that have accumulated over time. Peat is an excellent example of a loamy soil and is considered one of the best types of soil for planting.

TIP: Our expert gardening adviser, Rachel Klein adds, "The gardener's definition of humus and the scientific definition are actually very different. Bags labeled 'humus' at garden supply centers simply contain compost, formed through rapid decomposition of organic materials. Technically though, humus is organic matter that can no longer be broken down, or 'finished compost.' Fully humified organic matter is uniform in appearance; a dark, spongy, jelly-like substance. It is an amorphous structure and may remain that way for a millennium or more."

Comparing Peat to Humus

Peat is found in low-lying areas, especially in swamps, bogs and areas the are frequently flooded and drained. Sediments and minerals are picked up by water and then settle into the low area, concentrating highly fertile soil into small spaces. Peat is sometimes called humus but composting is the more accurate way of producing humus, which is generally used more as a soil additive than a complete planting solution. Humus contains decayed plant matter and may also be treated with manure, lime or other natural ingredients to modify the acidity or fertility content.

Benefits of Humus

Humus is one of the most beneficial additives to any garden. This stems from the high levels of nutrients and beneficial microbes it contains. The process that converts raw organic matter into humus feeds the soil population of microorganisms and other creatures, thus maintaining high and healthy levels of soil life. Humus can also hold the equivalent of 80 to 90 percent its own weight in moisture, increasing the soil's capacity to withstand drought. The structure of humus enables it to act as a buffer against soils that are too alkaline or acidic, and the dark color even helps to warm up cold soil in the spring.

Creating Humus Through Composting

Composting uses yard debris such as grass cuttings and household waste such as coffee grounds, vegetable peels and cores, old bread and newspaper. The debris is added to the compost mound and mixed in with the exiting material so that active microorganisms and air are spread throughout the pile. Decomposition occurs faster when the compost if mixed often. In addition to plant nutrients, composting allows concentrated growth of beneficial organisms, including bacteria and fungi, as well as ground dwelling insects and earthworms.

Humus is Alive

Humus is not just soil, it is a community of living things. Organic matter is a breeding ground for many types of microbes, including bacteria and fungi which break down plant material, and for other microorganisms that help plants roots absorb necessary nutrients. Earthworms have long been known to loosen the soil for plant roots. Recent research indicates that earthworms may serve to eliminate unwanted pathogens from the soil as well.

Ingredients of Humus

Healthy humus contains everything a plant needs to thrive. Nitrogen and oxygen are present in abundance, along with various amounts of potassium, magnesium and other minerals. Adding 1 cubic foot of clay every 3 or 4 months will help infuse trace metals and other inorganic compounds as well as naturally regulating the acidity of the humus soil. In all, humus contains more than 25 minerals and nutrients that plants need for proper growth.

TIP: Rachel says, "Humus is as good as it gets, nutritionally. However, humus cannot support healthy life on its own. It should make up only a certain percentage of ideal soil. Colorado State University has compiled a comprehensive guide to identifying the composition of your soil, which will help you figure out how much humus you need."

Applying Humus

To add humus or other compost into your garden soil, spread out a wheelbarrow full for every 10 square foot section of the garden and mix it in with a potato rake. More humus can be added as desired or available, and the amount here is a generally a minimum guideline. Soil can be mixed with a tiller, but emerging research indicates that tillers are too efficient and cause the soil to dry out, leaving it vulnerable to wind and rain erosion. Although it takes longer than a tiller, using a simple trowel to mix and churn the humus into the soil is the most effective method.

TIP: Rachel reminds you, "The successful gardener misses no opportunity to add organic matter to his garden."