While research has looked into how irrigation should be managed with various growing-media mixes, little has been undertaken on how different substrates interact with nutrients, which could have implications for fertiliser use.
As a start, in AHDB Horticulture project CP095, two trials compared the interactions of growing media, containing a range of ingredients, with organic or inorganic fertilisers and their effect on growth and quality of pelargoniums, to highlight any issues over the methodology for the main body of research. A large-scale trial on hardy nursery stock has since been established growing hebe and viburnum in 15 experimental media mixes.
The initial experiments showed how fertiliser type and growing medium could impact plant quality. In general, media type had little impact on plant quality when nutrition was supplied by inorganic fertilisers. However, quality was reduced where organic fertiliser was used. Also apparent was that, regardless of growing medium, doubling the rates of organic or inorganic fertilisers from those recommended by the manufacturers led to a marked reduction in plant quality.
There was limited scope to work out interactions in amateur products of inconsistent and variable nature. Batches of the same brand often showed large differences in physical and chemical characteristics.
"Understanding fertiliser interactions in peat-reduced or peat-free growing media is an important step in terms of plant growth management, and lessons gained from work with amateur growing-media products should prove informative to growers wishing to adopt new substrates." Neil Bragg, Bulrush.