Humus is the dark organic material that remains after most organic matter has decomposed. It forms in the soil when plant materials—such as fallen leaves and twigs—break down naturally. It also develops from the decomposition of dead organisms like insects. This decomposition process breaks matter down into its basic chemical components, which serve as essential nutrients for the soil and other living organisms.
The chemical composition of humus varies depending on the plant and animal materials from which it originated. Humus is broken down by earthworms, bacteria, fungi, and other microorganisms. It is mostly found in the top 5 centimeters of soil and is characterized by its dark brown to black color, loose crumbly texture, and sponge-like appearance.
Why Is Humus Important for Soil?
1. Soil Aeration and Structure Improvement
Loose, well-aerated soil allows plant roots to penetrate deeply and grow efficiently. It also provides more air pockets, which increases soil fertility and supports healthy plant growth. Soil can be aerated and improved by regularly adding humus around trees, shrubs, and garden beds.
2. Pest and Disease Control
Humus supports active beneficial microorganisms like ants and ground spiders, which feed on pest larvae living in the soil. It also encourages the growth of beneficial nematodes and certain bacteria used to combat white grub larvae and other soil pests.
3. Plant Nutrition
Humus contains essential nutrients such as nitrogen, phosphorus, sulfur, calcium, magnesium, and potassium. The natural acids found in humus hold and store these nutrients, especially in nutrient-poor soils. This helps plants access the minerals they need, particularly near their root zones.
4. Water Retention
Humus can hold up to 90% of its weight in water because of its sponge-like structure. This reduces the need for frequent watering during dry periods, as plant roots can access the stored moisture. This quality also improves the soil’s overall water-holding capacity and aeration.
5. Additional Benefits
Adding humus to amended soil protects and stabilizes pH levels. Its dark color helps absorb heat, warming the soil and promoting better plant growth.
How to Make Humus (Humus Compost)
Follow these steps to prepare humus at home:
- Choose a shaded, dry area away from the house to avoid unpleasant odors, and set up a large container or compost bin.
- Add an 8-cm layer of carbon-rich materials: leaves, straw, branches, wood chips, shredded cardboard, or paper.
- Add organic kitchen waste: vegetable and fruit scraps, tea bags, newspapers, and cardboard.
Avoid: dairy products, baked goods, meat, plastics, and synthetic materials. - Add an 8-cm layer of mulch after every 20 cm of organic waste.
After the first layer of organic waste, add an 8–10 cm layer of wood chips, straw, grass clippings, or leaves to balance carbon and nitrogen. - Turn the pile every 3 days using a shovel to speed up decomposition and reduce odors.
- Once the pile turns mostly dark, you can use it as compost.
For true humus, leave the pile for 6–12 months, allowing deeper decomposition. The longer the process, the richer and more beneficial the humus becomes.
