Humus

First, the spelling: humus is the rich material in your soil, not hummus, the chickpea dip. It is pronounced "hew-mus", and it is one of the most important things you can build in a garden — even though you can never buy a bag of it.

Humus is what is left at the very end of decomposition. When grass clippings, leaves, manure and kitchen waste rot down into compost, that compost is not the finished article. Once it is worked into the ground, soil life continues to break it down further until only a dark, stable, jelly-like substance remains. That substance is humus. Unlike fresh compost, it resists further rotting, so it sticks around in the soil for years rather than months.

Why humus matters

Humus quietly does several jobs at once:

• Holds water. It can absorb many times its own weight in moisture, acting like a sponge that keeps roots damp through a dry British summer — yet it also opens heavy ground up so winter rain drains away instead of sitting and turning the bed waterlogged.
• Stores nutrients. It clings on to plant foods that would otherwise wash straight out of the soil with the rain, then releases them slowly to your crops.
• Builds structure. Humus glues fine soil particles into small crumbs, giving you the open, crumbly texture that seeds and roots love. This is a big part of what makes a good loam so easy to work.
• Feeds soil life. Worms, fungi and bacteria all thrive in humus-rich ground, and their activity keeps the whole system healthy.

How to build humus

You cannot pour humus on from a bag — you grow it, by repeatedly adding organic matter and letting the soil do the rest. In practice that means:

• Spreading home-made or bought compost over your beds each year.
• Laying organic mulch such as compost, leaf mould or well-rotted manure on the surface and letting the worms pull it down.
• Avoiding heavy digging, which burns through humus by exposing it to air.

This is slow work — in the UK's cool climate, humus accumulates over seasons, not weeks — but it is cumulative. Keep feeding the soil and, year on year, it grows darker, springier and more forgiving, holding moisture in July and draining freely in January. A garden rich in humus is the foundation of healthy, low-effort growing.