Humus is the organic part of the soil formed by the decomposing action of soil microorganisms (bacteria and fungi) that break down animal and vegetable material.
This loose, crumbly material contains the elements that plants need to grow. The better the humus in your soil, the better your plants will grow. Without this decomposed material, soil is inactive and unable to produce plants.
Decomposed material is important because it retains moisture in the soil, loosens the soil for better air flow and drainage, and encourages the increase of soil organisms that help make nutrients available to plants.
In nature, humus is constantly introduced into soil as plant debris, dead animals, and other organic matter that decomposes on the ground. Historically, farmers added barnyard manure to the soil.
If you don’t have manure, you can use garden wastes in the form of compost. Start your own compost heap with leaves, grass clippings, weeds, spent flowers and vegetable plants, and even vegetable waste from the kitchen.