Planting density effects on root yield of purple coneflower (Echinacea purpurea (L.) Moench)

Dried root of the medicinal plant Echinacea purpurea (L.) Moench is used as an immune stimulant. Evidence from initial field trials in New Zealand suggested that root yield may be improved by planting at higher densities than commonly used. Plants were grown in raised beds 1.5 m wide at densities ranging from 1.5 to 65 plants/m of bed. Maximum root yield after two seasons of growth was c. 30 g/plant at the lowest densities, reducing to 5 g/plant at the highest densities. Maximum yields of 260 g/m of bed were achieved at densities of c. 20 plants/m of bed with no change at higher densities. Root yield as a percentage of root + rhizome yield increased from 45 to 65% as plant size diminished with increasing density. Changes in rootirhizome ratio with plant density are likely to affect alkylamide concentration.