Thursday 5 October, 2017

Blanket Bogs

Taken from: Bord na Móna Fact Sheet No.5

These can be defined as bogs which form in areas where relatively high levels of rainfall occur annually. They are found mainly on the lowlands in the western counties and also on mountain areas throughout the country. They are shallow bogs which form a blanket- like layer over the underlying soil. Their average depth is 2.6 metres.

Two types occur in Ireland: (See Fig. I)

(i) Low Level Atlantic: This occurs along the western seaboard in flat or undulating topography below the 150 m contour line. The rainfall in these areas is greater than 1250 mm per annum and the number of rain days exceeds 200 p.a.

(ii) High Level Montane: This type occurs extensively above the 150 m contour line in the western counties and also at the higher levels in mountain areas throughout the country. Rainfall in these areas is higher than (i) above.


In general, Blanket Bogs began to form about 2000 BC (i.e. 4000 BP) and consequently they are much younger than fens which formed underneath raised bogs. They were formed from vegetation which grew, in saturated conditions, with most of the nutrients being supplied by rainwater. The vegetation was of mixed composition, e.g. sedges, grasses, heathers and mosses. When this vegetation partially decayed and accumulated in annual cycles over thousands of years on the water­logged, anaerobic environment, Blanket Bog was formed.

Prior to the formation of Blanket Bog there is much evidence to show that pine forests covered much of the lowlands of the western counties and some pine and birch woods were common on hill slopes and hill tops. Therefore when Blanket Bog formed over these areas, the roots and stumps of these trees were covered by peat and their partially decayed remains can still be found at the base today. The peat which formed immediately over them is a highly humified (i.e. highly decomposed) layer of black peat which we call Blanket Bog 1 (i.e. B1). This layer can be between 1.5 and 2.0m deep.

A second layer, Blanket Bog 2 (i.e. B2) is the uppermost layer and is only moderately humified, as it was formed on top of, and in more recent times than B 1. B2 supports actively growing vegetation on its upper surface. The depth of B2 is between 0.5 and 1.0 metres.

Fact Sheet 5.1

Characteristics of blanket bogs
pH 4.8-5.6
Water Content (undrained) Approx. 93%
Solids Content (undrained) Approx. 7%
Organic Content (anhydrous) 2.6 m
Rainfall per year. Atlantic (i) >1250 mm; > Rain days
Rainfall per year. Montane (ii) Higher than (i) above
Growth of Vegetation Due mainly to high levels of rainfall


Uses of Blanket Bogs


  • The extensive Blanket Bogs which are located mainly along the west coast of Ireland are amongst our great natural assets; their uniqueness can be compared to the semi-tropical and tropical rainforests in a number of remote regions in the world. As they have taken approximately 4000 years to grow to their present state, it is extremely important that large representative examples of these peatlands are conserved.
  • Blanket Bogs can provide an interesting range of subjects for research purposes. Examples include: flora, fauna, ecology. Research into the causes of erosion on the montane bogs could be of great benefit in preserving these peatlands.



  • Milled Peat. This is an air-dried product which is supplied to power stations for electricity generation. This material when artificially dried can also be used for briquette manufacture.
  • Sod Peat. This product can be produced from Blanket Bogs where it is air dried and subsequently used as a domestic fuel.


Deer Sedge Cranefly
Purple Moor Grass Damselfly
Bog Cotton ​Dragonfly
Black Bog Rush Emperor Moth
Black Moss ​Black Slug
Sundew Common Frog
Butterwort Hare
Tormentil ​Otter
Milkwort ​Red Grouse, Snipe
Bog Orchid ​Golden Plover
Curlew, Skylark
Merlin, Meadow Pipit