Total biomass and annual yield of Drosera on cultivated Sphagnum in north-west Germany

Sphagnum paludiculture farms, where Drosera species grow spontaneously under semi-natural conditions, may provide fresh Drosera raw material for the pharmaceutical industry as a sustainable alternative to collecting Drosera from natural peatlands. We collected and measured the fresh mass of all plants of Drosera rotundifolia and Drosera intermedia growing in 1 m2 plots located in fields of cultivated Sphagnum palustre and Sphagnum papillosum, and thus calculated plant density, total biomass and harvestable yield (flowering plants only). We found significantly higher total biomass (433 ± 368 kg ha-1) and yield (292 ± 227 kg ha-1 yr 1) for D. rotundifolia compared to D. intermedia (68 ± 67 kg ha-1 and 56 ± 55 kg ha-1 yr-1) in July/August. The highest recorded total biomass for D. rotundifolia growing on S. palustre was 590 ± 342 kg ha-1. Total biomass and yield for D. rotundifolia were, respectively, 5–54 times and 3–29 times literature values reported for natural habitats in central and northern Europe. The effect of Sphagnum species was significant for D. rotundifolia, which achieved higher total biomass and yield in the S. palustre field than in the S. papillosum field. D. intermedia grew only in the S. papillosum field because the S. palustre field lacked suitable microhabitats. Highly productive populations of D. rotundifolia developed in both Sphagnum paludiculture fields two years after their establishment, but there was only a small population of D. intermedia at that stage. For commercial farming and sustainable production of D. rotundifolia we recommend its cultivation on S. palustre lawns, harvesting in July/August, and harvesting only plants that are more than 12 months old.