Repeat – From Industrial Residuals to Next‑Generation Growing Media

Swedish forestry relies on large volumes of tree seedlings grown in specialized growing media. Today, peat is almost exclusively used due to its favorable properties for plant growth. However, peat extraction has a negative climate impact, as peatlands are important carbon sinks. Restrictions on peat extraction are expected, creating an urgent need for sustainable alternatives.

This project explores whether residual materials from the pulp and paper industry can be used as alternatives or complements to peat in forest seedling production. The focus is on three forest‑based residual streams (bark sludge, fiber sludge and biosludge) that are currently underutilized, often being incinerated or disposed of despite their potential value.

The project applies a combined assessment of material structure, chemical composition and short‑term plant growth responses. This integrated approach allows for rapid identification of materials with high potential, while excluding unsuitable candidates at an early stage, thereby reducing the need for long and resource‑intensive growth trials.

Ensuring a reliable supply of sustainable growing media is essential for the future of forestry and the transition to a low-carbon society. By upgrading forest‑based industrial residues and returning them to the forest via seedling cultivation, the project contributes to reduced climate impact, increased resource efficiency and a more circular use of forest resources. The results may support further development of peat‑reduced or peat‑free growing media for sustainable forestry.