Peat moss is the dried residue of plants, mainly sphagnum moss, that has accumulated in bogs under acidic conditions. It has been a horticultural staple for many years, used to add water- and nutrient-holding bulk to potting mixes, as a mulch and as an acidifier for high pH soils. Ireland supplies more than half of the peat sold to British gardeners.
Types of Peatland
Fens develop in lake basins as they turn to marsh, may be acidic or alkaline and contain a thin layer of peat, about six feet thick.
Lowland lake basins may also become raised bogs, always acidic, with deep accumulations of peat, up to thirty-six feet.
Blanket bogs grow on upland mineral soils, always acidic, in areas of high rainfall, with layers of peat reaching eighteen feet.
Peat builds up slowly, a little less than half an inch every ten years, as dead vegetation accumulates because the waterlogged soil has no oxygen to support decay organisms.
Fens develop a layer of peat as the plants on the margins of a lake die and accumulate. Its pH depends on the groundwater that provides moisture and nutrients.
Raised bogs began to develop about 10,000 years ago as fen plant material built up beyond the influence of the groundwater, becoming acidic enough to support Sphagnum mosses and other plants unique to that environment. This type of peat is quite different from fen peat.
Blanket bogs began to develop about 5,000 years ago as a thin layer of iron accumulated and hardened, blocking drainage and allowing the cold upland soil to become waterlogged.
Horticultural peat is produced by milling, a process that begins with draining a bog, stripping the plants off the top and leveling it, then using machines to strip off the top half inch of peat. This is allowed to dry and then sucked up by a vacuum harvester. A bog may produce up to twelve harvests a year.
Historically, the main use of peat in Ireland was as fuel for heating homes, especially after the removal of the native forests. It has also been used as a bedding for livestock, a packing material and as a raw material to produce high quality charcoal. Since 1967, poorer quality peat has been burned to produce electricity.
British gardeners use over two million cubic yards of peat a year, ninety percent of the peat dug in Ireland for gardening. About two-thirds is bought by amateurs for home use.
Bricks of cut peat are still burned in some places in Ireland and exported to other areas of the world, including the US, as samples of Irish culture.
The destruction of bogs to produce milled peat far outstrips their natural regeneration. Raised bogs, in particular, support support unique colonies of plants and animals that may be irreplaceable. When a bog is cleared out only a sterile pit remains. The British gardening industry is trying to phase out the use of peat and encourage alternatives including coir and compost.