Evaluating peat-free substrates for sustainable cultivation of Tagetes erecta: growth, flowering, and physiological performance

Introduction: The production of ornamental container plants in peat-free substrates is essential for advancing sustainable horticulture, mitigating environmental impacts, and preserving valuable peatland ecosystems.

Goals: This study aimed to investigate the potential of growing Tagetes erecta ‘Antiqua Yellow’ in three different commercially available substrates: (1) a substrate with a 20% reduced peat content (P1), (2) a peat-free substrate with perlite (P2), and (3) a peat-free substrate based on wood industry waste (P3).

Methodology: The experiment was conducted from March 21 to May 30, 2024, in experimental greenhouses at the University of Agriculture in Krakow, Poland. Each treatment included four replicates of 25 plants grown on cultivation benches at a temperature of 18°C ±2°C during the day and 16°C ±2°C at night. After ten weeks of planting Tagetes erecta ‘Antiqua Yellow’ seedlings in the P9 pots (0.5 dm³), plant growth and development were assessed. The control group consisted of plants grown in a standard 100% peat substrate (PK). All tested substrates were enriched with dried and grounded mushroom (Agaricus bisporus) fruiting bodies (2.5% vol.) to be assessed as a potential biostimulator.

Results: The tallest plants were observed in the P1 substrate, while those grown in PK, P2, and P3 were approximately 2 cm shorter. The addition of the mushroom-based stimulator inhibited plant height but enhanced branching, although no substrate outperformed the control (PK), which demonstrated the highest tillering. Flower buds appeared fastest in the P3 substrate; however, all substrates exhibited visible flower buds by the third week. The development of flower buds to full bloom occurred most rapidly in peat-free substrates (P2 and P3) enriched with dried mushrooms. The best physiological parameters were observed in marigold leaves grown in the control substrate (PK), including chlorophyll fluorescence, SPAD readings, and photosynthetic pigment content (chlorophyll a, chlorophyll b, carotenoids).

Conclusions: While peat-free substrates demonstrated potential for supporting marigold growth and flowering, none matched the physiological performance or overall quality of plants grown in 100% peat. Future research should focus on refining alternative substrates to bridge this performance gap, contributing to sustainable horticulture practices.