There are many different types and qualities of high peat available. The characteristics of peat depend, among other things, on the depth from which it occurs, the method of extraction and climatic circumstances in the peat region. Working through the peat profile from the top down, we find the following types:
‘Upper layer’ of peat
The ‘upper layer’ is the top 10 inches of the peat profile. According to German peat cutting regulations this layer is removed and then should be laid back on the sandy bed after the white and black peat have been harvested. This layer contains upright stems from the sphagnum moss and is largely alive; water moves easily through this region. A disadvantage of the ‘upper layer’ of peat is that it does not always have a homogenous composition.
Sphagnum moss peat
Sphagnum moss peat is young, partially decomposed sphagnum moss that can retain between 10 to 12 times its own weight in water. It has a light colour and is made up almost entirely of different types of sphagnum moss. Because sphagnum moss peat is a relatively young organic material, it degrades more quickly than older types of peat. Sphagnum moss peat is the majority peat in the high quality sorts of potting mixes at present.
Peat litter or peat dust is extracted from the top layer of the peat profile. The product is light brown and only slightly decomposed. Peat litter can retain at least 8 times its own weight in water. Water uptake and release is a slower process in this peat than in sphagnum moss peat. Peat litter is available as fine, normal and coarse. The grade depends on the method used for extraction.
The fine grade is extracted horizontally with the peat being cut out layer by layer, then dried and harvested. This is the cheapest method. In order to produce a larger coarse grade, the more expensive vertical pitch method of extraction has to be used.
Black peat (non permafrost)
Non-permafrost black peat, which is also known as old peat, champ peat or casing soil peat, is not suitable for potting soil because it shrinks greatly when it dries and thereafter has low water retention levels. When it is thoroughly dried, it becomes very hard peat (pressed peat) that can and is still used as fuel.
Garden peat is an important source for the potting soil industry. It is produced by allowing wet black peat to freeze. The quality of the garden peat depends on the extent to which it has been frozen. Freezing black peat improves its water retention qualities and reduces shrinkage. After drying garden peat can take up at least 4 times its own weight in water. Garden peat is dark brown, which is a good indication that it has already reached an advanced stage of decomposition. It consists of very fine particles, which gives it a relatively low air content.
‘Coloured’ or ‘grey’ peat comes from the layer between the white and black peat layers. This layer has decomposed further than the white layer and its colour lies between the white and black peat. ‘Coloured’ peat can retain less water than peat litter and sphagnum moss peat.