Olive-mill wastes compost as growing medium component for the production of poinsettia

The research work was conducted in order to investigate the possibility of using olive-mill wastes compost (OWC) in the production of ornamentals replacing part of the peat in the growing medium. Rooted cuttings of Euphorbia pulcherrima cv. Peterstar white were grown in media containing OWC, peat and perlite in various ratios, and their vegetative growth, root growth and flowering was determined. A medium of 1 peat: 1 perlite (by volume) was used as control. Increasing replacement of the peat in the medium by OWC, up to 75%, caused analogous increase of the electrical conductance that was however rapidly reduced during the culture period. A total of 50 and 75% replacement of peat caused decrease of the total porosity and the easily available water. Increasing replacement of peat by OWC induced a gradual decrease of the plant height, bract number and node number where the first bract was initiated. All the above parameters of growth were significantly reduced even when 25% of peat was replaced, except the bract number that was significantly reduced only in case of 50% or more peat replacement. Root dry weight was reduced only when 75% of the peat was replaced. The restriction of vegetative growth occurred only during the first month of culture in media with 25 and 50% peat replacement, while in 75% replacement there was growth restriction all over the culture period. Media with 50 and 75% peat replacement caused delayed pigmentation of the bracts and flowering, while plants in the medium with 25% peat replacement showed colour and flowered simultaneously with the control. (C) 2004 Elsevier B.V. All rights reserved.