The structure of potting soil determines how much water and air are available to the roots. Air is important for the roots’ oxygen supply and for the micro-organisms in the root environment.
Roots need oxygen for growth, maintenance of the root system, and the uptake of water and nutrients. The provision of a good supply of air for fast growing plants is of vital importance for obtaining good results. A shortage of air in the early stages of cultivation leads to a poorly developed root system, which hampers growth resulting in a smaller yield.
Air (Oxygen) moves from the air supply outside or in the growing room, through large pores in the medium to the root surface by diffusion. The structure of the potting soil in use is dependent on the quality of the raw materials comprising the soiless potting mix. The best soiless potting media starts with virgin peat that has long-term stable structural characteristics.
Vertically cut or shaved peat?
Two different methods of harvesting can be used to exploit peat deposits: the cheapest but least efficient method consists of “shaving off” the top layer of peat. The disadvantage of this technique is that the structure is less coarse which has an undesirable effect on the air/ water relationship.
The second method consists of cutting the peat vertically. This is the most well known method from times past. The peat blocks that were previously used as fuel for cooking and heating houses were cut in this way. This is an expensive way of extracting peat. When peat is cut into blocks it has to be turned by hand to dry out.
The coarser the peat is, the better will be the balance between the water and air it contains. This ensures the roots develop better in the medium. The plants are healthier and the tendency of the mix to compress is reduced.
High and low
One of a potting medium’s main ingredients is peat. This is a century’s old, naturally occurring material formed from old vegetation. Peat originates from regions where climatic circumstances caused new plant material to form faster than the dead vegetation could rot. Slowly but surely this process built up a layers of organic materials that become several metres deep in some locations.
Two different types of peat can be differentiated: high peat and low peat. Low peat is formed in regions where groundwater levels are high and there are plenty of nutrients. Low peat typically contains a high proportion of rotten material and can have high levels of silt; sand and harmful salts which makes it an unsuitable base for a good potting soil.
High peat is formed under the influence of rainwater in low nutrient regions and its principal ingredient is sphagnum moss. This is a small plant that dies off from below while continuing to grow above on its own remains. The remains of other plants are also found here; grasses, tree limbs and leaves for example.
Sphagnum moss is particularly suitable for use as a growing substrate because it is natural, light, clean and easy to work with. It has a low nutritional content; a pH that ranges from 3.5 to 4.5 and has good water retention properties (up to 20 times its own weight). The profile of high peat in the flat peat region of Northwest Germany, contains different, distinct layers that formed in different periods.