The most important raw material for potting soils is peat. Each year millions of cubic meters of peat are used in Europe that come from the Baltic States, Sweden, Finland, Russia, Poland, Germany, Ireland etc. (Holland imports yearly about 5.000.000 m3 and Europe around 18.000.000 m3). The types of peat moss differ from country to country because of the different types of Sphagnum and the different climates. Therefore also the characteristics differ per country. Even differences in peat from the same peat bog can be found. To make things even more complicated, there are also different ways of harvesting the peat which results in (again) different characteristics.
White peat milled
Most of the white peat is milled, that means that the upper layer is milled loose so that it can dry easier. When the upper layer is dry, the peat is “turned” and if the complete upper layer is dry enough, the peat can be harvested. This is often done with special machines that gather the peat and store it in big heaps. Because this “milled white peat” is price wise interesting, it is used on a big scale in the professional horticulture. Besides the interesting price, there are some points of attention here; especially when its origin is the Baltic States (but also in Canada you can encounter the same problem), we see that often the peat is hydrophobic which means that it will have difficulties to absorb water after drying out. Another threat is the “turning” of the peat; when rain falls, after turning, the whole drying process starts again. When this “turning” has to be done often, the structure of the peat will be more fine, which is not preferred in most potting soils. For that reason it is possible that the potting producer receives a different type of white peat in may than he receives in September, although from the same peat bog. Fortunately the professional peat producers have big stocks so that eventually a uniform product can be delivered.
White peat blocks
Another way of harvesting white peat is producing peat blocks. In this case, the upper layer will not be milled but blocks are cut out of the profile. Later on these blocks will be stacked in such a way that they can dry easy and while drying out, the blocks will shrink so that stronger fractions can be taken out of the blocks, later. After drying, the blocks are sent to the potting soil producers. The advantage of these blocks is the superior structure; the fines which are found in the milled peat are much less and – although the drying of blocks takes some more time – one small shower does not bring the producer back to the start. For the potting soil producer the advantage of the blocks is the fact that better and stronger “fractions” subtracted. Even the finest fraction will contain more air than milled peat. A disadvantage for the peat producer is the extra labour; cutting it out of the peat bog takes more time, stacking it in rows also requires more labour and therefore: more money. For the blocks the background of the peat is very important for the structure and of course the humidity of the blocks. When the blocks are too humid, the fractions will be softer and smaller and when used by the grower, hard to find.
Black peat is a frozen peat which is found in Germany. Here the climate is an important factor as black peat is naturally irreversible which means that black peat will retract when it dries out, but to get back its old shape – when you want to rewet – it is not possible. In the past, when black peat blocks were cut out of the fields, they were dried and these blocks were excellent for burning as the caloric value is high. Nowadays, when we produce black peat for horticultural purposes, we don’t want this characteristic and therefore the black peat should be frozen. When the black peat is well frozen, this “irreversibility” is a factor anymore and it can be used.
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