Effect of growing media composition, compaction and periods of anoxia on the quality and keeping quality of potted roses (Rosa sp.)

The significance of growing media composition on plant growth and subsequent keeping quality was examined with special emphasis on variation in oxygen content in the media. The oxygen content was determined in situ by fixed oxygen sensors and by a novel approach determining oxygen profiles by microsensors. In the first experiment, 6 different peat based growing media were examined: (1) standard fertilised peat mix for rose production, (2) fertilised peat with no amendments, (3) fertilised peat with 6kgm⁻³ clay powder, (4) fertilised peat with 6kgm⁻³ clay powder and 40kgm⁻³ 2-4mm clay granules, (5) fertilised peat with 40kgm⁻³ 2-4mm clay granules and (6) fertilised peat and 25% coir (v/v). In this experiment, the oxygen content was determined by fixed oxygen sensors 1cm above the bottom of the container during plant growth. In the following experiment, 3 different media were examined: (1) standard fertilised peat mix (10% perlite) for rose production, (2) fertilised peat with no perlite and (3) fertilised peat with 25% perlite (v/v), compacted 0%, 20% or 40%. Here, oxygen profiles from the top to the bottom of the container during irrigation cycles were determined by microsensors. After production, the quality (fresh and dry weight, number of flowers and buds and number of shoots) as well as the keeping quality of the plants were determined. The sensors placed at one point revealed oxygen fluctuations with short periods of low oxygen availability corresponding to fluctuations in water content during the irrigation cycles. The microsensors provided a more detailed description of oxygen distribution in the media, showing periods of hypoxia or even anoxia in the bottom of the pots after irrigation. Despite substantial differences in growing media composition and periods of anoxia in the bottom of the containers no effect was seen on plant quality or the subsequent keeping quality.