Optimizing seed-based Miscanthus plug plant production with supplemental heat and light, compost type and volume

To help meet greenhouse gas mitigation targets perennial biomass crops will need to be planted at large scales and at a much greater pace over the coming decades. Miscanthus is a leading biomass crop but rapid upscaling is technically challenging due to costly and time-consuming clonal propagation. Seed-based hybrids are considered a viable route to rapid upscaling, but direct sowing has not been found feasible under temperate climate conditions due to high thermal requirements for germination and slow early plant development compared with larger seeded annuals. Seed-based plug plants, initially propagated in greenhouses, provide a suitable route to improve field establishment. Here, we describe an input optimization experiment for seeded Miscanthus plugs raised for spring planting in a naturally lit greenhouse with the following treatments: supplemental heat to maintain a minimum of 15°C, supplemental predawn light from modern LEDs at PPFD 300–400 μmol m−2 s−1, two proprietary types of compost (known as 50k and 70k), and two compost volumes (35 and 15 cm3). Our results showed that variations in all four factors had significant effects on above- and belowground biomass: (i) supplemental heat increased root-to-shoot ratio, (ii) supplemental light increased total biomass and root-to-shoot ratio, (iii) compost type affected total biomass and (iv) compost volume was positively correlated with total biomass and stem base diameter. No factor had a significant effect on axillary shoot formation. We recommend nurseries in the United Kingdom use LEDs as predawn supplemental light but no supplemental heat, compost that has both good water-holding capacity and aeration, and a larger compost volume, which provided optimized cost-plug resilience for spring-sown, seed-based Miscanthus plug production.