In drained peatlands, tree growth is often restricted by the lack of potassium and phosphorus. The best fertiliser for nutrient-poor peatlands is high-quality wood ash, which usually contains all the nutrients in the right proportion trees require. Ash fertilisation helps rectify tree growth far into the future, for as long as 50 years. Forest owners can apply for subsidies for the costs of corrective fertilisation of peatlands under the Sustainable Forestry Financing Act.
Ash fertilisation is well suited to wooded, nitrogen-rich thick peatlands. Previously, drainage repair was often carried out in peatlands in connection with corrective fertilisation, but based on current knowledge, drainage is not particularly useful for tree growth if the water surface is already more than 30 centimetres below ground level.
Fertilisation spurs forest growth. Since a forest that is in good condition and grows well evaporates more water and keeps soil moisture well balanced, drainage repair is not always necessary. Unnecessary drainage repair results in more carbon being released due to the decomposition of peat. It also poses a risk of increased impacts on waterways.