Humus Soil 101

Humus Soil
What You'll Need
Yard waste
Potato rake

Firstly, humus is not actually type of soil, but is rather a form of mature compost. It can be made either through a composting process or can be found in nature, such as in the rich topsoil found in some forests. Humus is one of the most nutritious planting materials around and is used for planting as well as for treating soil.

It is important to note that the gardener's definition of humus and the scientific definition are actually very different. For example, if you were to visit your local garden supply store and examine a bag labeled 'humus,' it would likely only have that name because the bag would contain compost, formed through rapid decomposition of organic materials.

Technically though, humus is organic matter that can no longer be broken down; in other words, it is 'finished compost.' Fully humified organic matter is uniform in its appearance as a dark, spongy, jelly-like substance. True humus has an amorphous structure and is so broken down that it may remain amorphous for a millennium or more.

Benefits of Humus

Humus is effective due to 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 of 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.

Drawbacks of Humus

If there’s one thing humus lacks in the gardening world, it’s that it’s still primarily an additive. Despite how effective it can be, it’s not generally used as a planting solution.

Creating Humus Through Composting

Composting attempts to repurpose yard waste such as grass cuttings and household waste such as coffee grounds, vegetable peels and cores, old bread, and newspaper. If a material is deemed compostable, it’s 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 is 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

Earthworms wiggling in the dirt

Humus is not just soil, it’s a community of living things. Organic matter is a breeding ground for many types of microbes, including bacteria and fungi that break down plant material, and for other microorganisms that help a 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. In all, humus contains more than 25 minerals and nutrients that plants need for proper growth.


As stated earlier, humus is just an additive at the end of the day. Other basic gardening soils like clay soils, sandy soils, and loamy soils are all planting soils that react differently with humus.


One cubic foot of clay every 3-4 months will help infuse trace metals and other inorganic compounds. Clay will also naturally regulate the acidity of the humus soil.


Peat is found in low-lying areas, especially in swamps, bogs, and areas 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

NOTE: Humus cannot support healthy life on its own. It should make up only a certain percentage of ideal soil.

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.