Planting clonal shade-tolerant herbs in young urban woodlands—Effects of compost on plant growth, flowering and survival

•Planting in compost is an effective method for establishing herbs in young woodlands.•Composting bridges the timespan until stable humus layer develop in young woodlands.•The method can support amenity and ecosystem values of young woodlands and parks. Rich herbaceous layers supply important ecosystem functions and amenity values in urban woodlands. However, due to poor dispersal and recruitment, typical woodland herbs often remain absent in woodlands established on post-agricultural and post-industrial sites, especially in fragmented urban landscapes. Efficient methods for active restoration of the herbaceous layer are therefore needed. In a plantation experiment in an 11-year-old oak stand established on post-agricultural land just outside Malmö City, southern Sweden, this study investigated the effects of compost addition and weed control on post-planting survival, growth and flowering of three typical shade-tolerant woodland herb species: Galium odoratum, Lamiastrum galeobdolon and Stellaria holostea. Removal of competing weed vegetation did not affect plant performance, but compost addition dramatically increased growth and flowering of all three species during the first two growing seasons, and also increased survival in S. holostea. This positive treatment effect probably derived from a more suitable top soil structure and a higher soil moisture in the compost treatment. We conclude that combined use of planting and composting is an effective method for rapid achievement of profusely flowering carpets of summer-green woodland herbs, which can provide important amenity values in the many woodlands established in and around cities in north-west Europe in recent decades. The method may also be applicable in other woodland restoration projects, where it can promote colonisation by typical shade-tolerant woodland herb species.