Humous has been hailed as a miracle soil ingredient, a nutrient-rich, spongy material that will deliver almost permanent benefits to the soil.
But recent research has thrown this belief into question, with some scientists even declaring the ‘death of humus.’ So, does humus even exist – and does it even matter?
What is humus?
The traditional and scientific definition of humus is a dark, organic material that consists of partially decomposed plant and animal matter. It is uniformly black or a dark brown in colour, and has a spongy texture.
However, in older composting literature the word humus has also been used to refer to actual compost, adding to the confusion around the term.
Scientists used to argue that humus may take years or even millennia to decay, as it resists breakdown by microorganisms. Other sources stated that it is a source of valuable nutrients that feed the same microorganisms.
The controversy around humus
Here’s where the controversy begins. Humus is supposed to be formed of long, recalcitrant carbon molecules – i.e. molecules that don’t break down.
Yet when scientists study soil or compost, they can’t see those molecules. This has led some scientists to announce “the death of humus”.
Despite the failure of modern scientists to detect humus, the term continues to be used by some composters.
Do you need to worry about humus in compost?
I am fascinated by the science of composting, but the reality is you don’t need to know much about definitions to get great compost. As long as you apply some simple principles such as sufficient air, moisture and insulation, you will still get an excellent soil amendment.
The same goes for humus. Going on recent literature, it probably doesn’t exist, but whether it does or not won’t affect your ability to carry out dramatic improvements to your garden.
FAQs
What is humus compost?
Humus compost is a term often used to describe rich, dark, organic material created through the decomposition of plant and animal matter. However, it’s important to note that the concept of “humus” is surrounded by some controversy in modern soil science. While traditionally thought to be a stable, long-lasting substance that resists decomposition, recent studies suggest that organic matter in compost is continually breaking down rather than forming a distinct layer of humus.
What is humus soil?
Humus soil refers to soil that is rich in organic matter, often described as dark, crumbly, and nutrient-dense. This type of soil is highly valued by gardeners because it retains moisture well, supports beneficial microorganisms, and provides essential nutrients to plants. However, as explored in the article above, modern soil science challenges this idea, suggesting that organic matter in soil is constantly breaking down rather than forming a separate “humus” layer.
Related articles
What is compost? It’s more controversial than you might think…
External resources
Garden Myths: Humus Does not Exist – Says New Study
National Geographic: Humus
Lehmen and Kleber, 2015, Nature: The contentious nature of soil organic matter
Gabriel Popkin, Quanta Magazine, 2021: A Soil-Science Revolution Upends Plans to Fight Climate Change