The Power of Humus



Humus takes the things that plants need to live and places them within easy reach of the roots. Adding it to your soil is a long-term project.



As we peruse our gardening books every spring, we frequently contemplate ways to improve our soil. One of the words that we often stumble across in the soil context is humus.

Somewhere in the back of our minds, we typically associate humus with good, rich garden soil. However, there is more to it than that.

A Gardening Vocabulary Lesson

Humus, to put it as simply as possible, is the part of the soil that is without structure and is made up of the entirely decomposed remains of plants and animals.

Part of the reason that humus is difficult to define is that scientists do not entirely understand what it is. It is distinct from organic matter because it has no shape or structure—not even cells. However, it is nevertheless derived from organic matter.

There are a number of related gardening terms that can cause confusion:

  • Organic matter. Organic matter is still in a state of decomposition. Some of the ingredients that went into it can be identified and separated from the rest.
  • Compost. Compost is made up of organic matter. It also contains particles of residue that can be further decomposed. To the naked eye, finished compost may present no signs of the organic matter that went into it, but there are still microscopic structures present that are not found in humus.
  • Peat. Peat is a constant source of confusion to gardeners. Peat moss is not peat humus, and peat humus is not humus at all. Peat moss is partially decayed sphagnum moss, a species of moss that grows in bogs. Peat humus is a combination of sediments and more thoroughly decayed peat moss that collects at the bottoms of bogs.

And as for the bagged humus that you picked up off the shelf, that was probably nothing more than compost. A looser definition of the word humus is typically used for commercial purposes.

Gardeners should note that no soil is entirely made up of humus. It is just one of the many ingredients that go into a healthy garden soil.

Benefits of Humus

Contrary to popular belief, humus contains no nutrients, since it is fully decomposed. Instead, this structureless substance paradoxically plays more of a structural role in garden soil.

The following are a few of the functions that humus serves:

  • Adding to soil density.
  • Giving the soil a loamy texture.
  • Absorbing heat from sunlight.
  • Retaining moisture.
  • Retaining the nutrients found in other parts of the soil.

In short, humus takes the things that plants need to live and places them within easy reach of the roots. Scientists also believe that this substance may have a hormone-like effect on plants, regulating their growth and reproduction.

How to Make Humus

Real humus cannot be purchased. Nor can it be created overnight. Adding this powerful substance to your soil is a long-term project.

Although neither organic matter nor compost are humus, they are the first steps toward creating it. In fact, mature compost typically has humus in it. By continuing to add organic matter and finished compost to your garden soil, you are slowly increasing the amount of humus, as well.

The good news is that humus is extremely stable. Even though it takes a long time to add humus to the soil, it will be there for many, many years to come, helping your plants find the nutrients and moisture that they need to thrive.

Helpful Resource

Soil Quick Start
More resources on improving your soil with humus and compost.

Improving Your Garden Soil