Compost important component in peat-free potting soil

26 September 2022 - Published by Hanne Lakkenborg Kristensen
Written by Wilco Dorresteijn, Delphy.


More than 70 growers recently visited a meeting about peat-free cultivation. Soilcom partner Delphy has been researching growing on peat-free or peat-poor potting soil at the Research Nursery for Tree cultivation and Perennial cultivation for several years now. Delphy mentions compost as an important ingredient to make the potting soil heavier and more moist.

The use of peat in potting soil is subject of social and political debate. Particular, large retailers set requirements on the potting soil in which plants are grown. The availability of peat is also a point of attention. In current practice, the use of compost in professional potting soils is still limited because compost makes the mixture physically heavier and wetter. Peat is then preferred because of its good physical and chemical properties.

Delphy does research,  looking into peat-free cultivation. And carries out trials in the context of the Soilcom project and for peat manufacturers. The experience and knowledge is increasing. When switching to peat-free or peat-free mixtures, the physical, chemical and biological properties of the potting soil will change. Various materials such as bark, wood fibre, coconut, perlite and rice chaff can quickly make peat-free potting soil too light and airy. This appears to be favorable for rooting, but too light potting soil is not desirable because of rapidly drying out, blowing over and a poor shelf life in the chain. Compost in the soil can make the mixture more moisture-retaining and heavier.

Various Delphy tests show that peat-free cultivation is possible, as long as the growers monitor the cultivation more intensively. And, if necessary, make timely adjustments in terms of watering, fertilization and pH. When it comes to compost, it is important to use certified compost and in the right proportions.