The Sphagnum Bog, West Meadow, Kenwood Estate
Sphagnum is a spongy, usually waterlogged, green moss.
It’s success depends on copious supplies of water.
Hampstead Heath has its very own sphagnum moss bog.
This may seem unusual, since the word “heath” suggests well drained, sandy soil, supporting plants such as gorse and heather, not sphagnum.
So why is it present?
Due to the geology.
The upper parts of the Heath are indeed drier because the underlying soil and “rock” are Bagshot Sands.
However, within those sands, there are thin bands of clay.
These clay bands locally prevent groundwaters from sinking further, and as a result, waters collect above the clay layers, where they can provide mosses such as sphagnum with all the moisture required for successful growth.
This is called a “perched water table”.
Where is the sphagnum?
As sphagnum would not be expected to occur on dry heathland, when it does occur, it is sufficiently unusual for it to be registered with English Nature as a Site of Special Scientific Interest (S.S.S.I).
On this count, it isn’t somewhere that should be too “public” or visited, in case it should be damaged.
It is no secret, however, that the site is in the upper part of West Meadow, clearly visible from the scenic path winding its way to Kenwood House from the Hampstead Gate.