Dirk Röse

Why is frost so important for black peat?

Our raw materials

Black peat is an important raw material for the production of growing media. It confers ideal properties for the cultivation of young vegetable plants, and also forms an integral part of substrates used for growing bedding and pot plants. Black peat is also an important component of container substrates for longer-rotation crops, and is indispensable for commercial horticulture.

Winter is the crucial season when it comes to optimising the quality of black peat. Prolonged periods of frost are ideally conducive to generating the desired properties for this raw material. It needs to be frozen right through to ensure the necessary physical parameters and to activate growth-promoting humic acids. Why is this? And what happens to the black peat when it freezes?

As soon as the black peat has been extracted using an excavator, the turves, saturated with water, are laid out on the bog surface. In frost conditions, when the black peat freezes thoroughly, its structure and properties alter: the water in the peat becomes ice, a process associated with physical expansion. When frozen, the black peat’s volume expands by around 9%, resulting in two advantages: the air capacity improves from 5 to 10% by volume, and the water storage capacity increases to > 400 g/100 g of dry matter (> 65% by volume). High water and air capacity are key criteria for high-quality growing media, as they have a highly positive impact on plant growth. The structural change caused by freezing is permanent, with the frost preventing irreversible shrinkage of the black peat.

Frost also causes the humic acids in black peat to decompose. They have a high cation exchange capacity, binding nutrients and specifically making them available to plants during their growth phase. Humic acids also stimulate root growth. These characteristics make black peat an extremely important substrate ingredient, with frost playing the crucial role.

However, in view of the increasingly mild weather conditions during the cold season, the question arises: can it be ensured that black peat will indeed continue to freeze over the long term? Bert von Seggern, Head of the Land Use Division, is confident that Klasmann-Deilmann is well prepared: “We always make provision to have several years’ worth of black peat supplies in storage, so that we can cope well with occasional frost-free winters.” The company is also ready to face more frequent mild winters: “We are now able to provide an excellent black peat, which has comparable properties, even without sufficient frost periods. Admittedly, though, the extraction process is more input-intensive and the raw material more expensive. So it’s good to know that additional resources are available to us from the Baltic region, where frost is guaranteed.”