Things to be aware of when using potting mixes
Prevent damage!
Peat is naturally quite acidic (pH 3.5-4.5) so lime must be added to raise the pH. Off the shelf potting soil always contains lime. The amount of lime that must be added depends on the composition of the peat. For example, garden peat always needs more lime than peat litter to raise the pH. On average potting soil needs 5 – 6 kg of lime per m3 (1,000 litre) to increase the pH. After adding the lime it will take a few weeks for the pH to stabilise. If no lime is added, or not enough, high concentrations of elements such as manganese, iron and phosphate will be absorbed and this may lead to signs of over feeding being seen.
The concentration of aluminium can rise to toxic levels for the plant, causing root thickening, which will restrict food intake. If your potting soil’s pH is too low the addition of 20 grammes of lime (Dolocal) per 10 litres will raise the pH one point. The correct degree of acidity for potting soil is between 5.8 and 6.2. Values higher than 6.2 can lead to phosphate being deposited in the form of calcium phosphate making it less accessible to the plant.