Moss is easy to overlook and has been quietly useful for a very long time. A tour of what it does, in the wild and in our hands.
Peat and carbon
Sphagnum mosses build peat, and peatlands store more carbon per hectare than forest. Healthy bogs are one of the most effective carbon stores on land, which is why draining and digging them is so costly, and restoring them so valuable.
Water and floods
A moss layer holds huge amounts of water and releases it slowly. On hillsides and in bogs this slows run-off, steadies streams and reduces the spikes that cause flooding downstream.
Insulation and packing
Dried moss has chinked log cabins, stuffed mattresses and packed shipped plants and bulbs for centuries. It is light, springy, holds moisture and is mildly antiseptic.
Wound dressings
Sphagnum is absorbent and slightly acidic, which discourages bacteria. It was gathered by the sackful to dress wounds in the First World War when cotton ran short, and it genuinely saved lives.
Pollution monitoring
Because mosses feed straight from air and rain, they accumulate whatever is in them. Scientists use moss samples to map heavy metals, nitrogen and other airborne pollutants cheaply and over wide areas.
Green roofs and walls
Light, drought-hardy once established and needing none of the upkeep of sedum or grass, moss carpets cool buildings, hold rainwater and add habitat, all for very little structural load.
Gardens and bonsai
As a living mulch, moss keeps roots cool and damp, suppresses weeds and finishes a planting. It is the quiet groundwork under a great deal of fine container growing.
Habitat
A moss carpet is a small world: a humid refuge for springtails, mites, tardigrades and the creatures that eat them, and nesting material for birds. Lose the moss and you lose that layer of life.
The long view: peat and climate
The grandest thing moss does happens over thousands of years and out of sight. In waterlogged bogs, sphagnum grows at the surface while its older growth beneath fails to rot in the airless, acidic conditions, and that half-preserved material piles up as peat. The result is one of the planet's great carbon stores, holding more per hectare than woodland, alongside an enormous capacity to soak up and slowly release water. Drain a bog or cut it for fuel and that carbon escapes to the air; keep it wet and it goes on quietly banking the stuff. Much of the modern argument for peat-free compost rests on this, and there is a fuller account in sphagnum, peat and why peat-free matters.
A history of practical use
People worked out the useful properties of moss long before they understood the biology. Its springiness and water-holding made it a packing material for everything from shipped bulbs to crockery, and a stuffing for mattresses and pillows. Dried and rammed between logs, it sealed cabins against the weather. The most striking use was medical: sphagnum's acidity and absorbency make it hostile to bacteria, and when surgical cotton ran short in the First World War, volunteers gathered bog moss by the cartload to dress wounds. There is more of this story in moss through history.
Moss in modern hands
Today the interest runs in two directions. Scientists read moss as an instrument: because it takes everything from the air and rain, a moss sample records the heavy metals and nitrogen drifting over a place, which makes for cheap, wide-area pollution mapping. Designers, meanwhile, treat it as lightweight green infrastructure, carpeting roofs and walls that could never carry a conventional planting, cooling buildings and catching rainwater for almost no structural load. And in the ordinary garden it remains what it has always been, a living mulch that keeps roots cool, smothers weeds and quietly finishes a planting.