Unlike hummus, humus is not very tasty with pita chips and feta cheese. It is, however, one of the most important components of healthy garden soil. Humus is the fully-decomposed remains of plant and animal life, broken down by bacteria, fungi and oxygen through a process called humification. What’s left after humification is the dark brown or black product of a well-managed compost pile or nature’s circle of life. Ideal garden soil contains 5-10% organic matter, and humus is a critical subset of that organic matter.
Scientifically speaking, humus made up of very long carbon molecules with an electrically charged surface area that can hold mineral particles, keeping them handy for plants to take in as they need them. Potassium, calcium, sodium, magnesium, iron and hydrogen are all nutrients that are captured and carried by humus in the soil, so a shortage of humus can lead to a deficiency of these nutrients. In addition to its mineral attraction capabilities, humus also houses tons of beneficial soil microbes in its sponge-like nooks and crannies. Oxygen hides out in humus spaces, too, which allows aerobic microbes to breathe. The microbes leave secretions that help glue soil particles together into aggregates for improved soil structure and decreased erosion.
Humus also helps soil retain water; the same tiny spaces that house microbes make space for water in the soil. In fact, humus can hold up to 80 to 90% of its weight in water. In sandy soils, adding humus helps keep water from draining out of the soil too fast. In clay-rich soils, humus breaks up the particles to allow water to penetrate into the soil to plant roots. In short, humus is hugely important – more humus means more microbes and better soil structure, which means healthier soil and more amazing plants.