THE USE OF GREEN COMPOST IN THE PRODUCTION OF CONTAINER NURSERY STOCK IN THE UK: CHALLENGES AND OPPORTUNITIES

ISHS Acta Horticulturae 819: International Symposium on Growing Media 2007

THE USE OF GREEN COMPOST IN THE PRODUCTION OF CONTAINER NURSERY STOCK IN THE UK: CHALLENGES AND OPPORTUNITIES

Author:	A. Rainbow
Keywords:	peat-free, growing media, bulk density, liverwort, CAT extraction, handling, disease suppression
Abstract: A comprehensive programme of 29 trials involving container nursery stock has been carried out on 25 nurseries using 267 subjects to assess the use of green compost in peat-free and peat-reduced growing media. The trials encompassed diverse geographic locations, potting methods, irrigation systems, environments (outdoor, glasshouse and polythene tunnel) and end-markets (retail and landscape). Seven green composts were used, all accredited to the UK PAS 100 standard. Green compost was usually incorporated into growing media at 33% v/v. Apart from nitrogen, the green compost provided all base nutrients and the usual, controlled-release fertiliser was added to all treatments. All trials used a peat-based medium as control. The main trends are summarised as follows: Despite bulk density of the peat-free medium being 30-50% higher than the peat-based medium, handling properties were acceptable (manual and machine-aided potting). Furthermore, the difference was reduced at potting (peat-free, for example, compressed less) and reduced further on watering. Where growth of liverwort or moss occurred on the surface of peat-based media, it was frequently suppressed in peat-free and peat-reduced media. Reduction in foliar disease (notably, Xanthomonas hederae) was seen in a few crops raised in peat-free media. No slumping or N starvation was observed. All plants raised in peat-free and peat-reduced media were marketable. Internodes were sometimes shorter in plants raised in peat-free and peat-reduced media (often welcomed by the grower). Despite the absence of wetting agent, peat-free and peat-reduced media retained water well, whether applied by overhead means (spray lines), trickle nozzles or capillary methods (sand bed or matting). Peat-free mixes seemed to require slightly more frequent irrigation but used no more water overall. Experience suggests that good quality green compost can be a cost-effective part alternative to peat in growing media for container nursery stock.
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