EFFECT OF DIFFERENT PEAT-BASED SUBSTRATES ON POINSETTIA GROWTH

          Five peat-based growing media were used in poinsettia (Euphorbia pulcherrima ‘Cortez’) cultivation under natural light conditions (54º N latitude) in September through December 2000. Two light peats extracted in north part of Poland (highly and weakly humified, H3-H4) were compared with two Latvian sphagnum peats (H2) of course (0-30 mm) or fine (0-7 mm) structure and ready-to-use poinsettia substrate manufactured of different fractions of sphagnum and light peats, containing also the cotton grass. Physical properties of all substrates were very good. Small differences in porosity and air-water relations did not have a significant impact on plant growth and final ornamental quality. Higher decomposition rate of Polish peats decreased the total porosity by 3-6% in comparison to other substrates, but did not influence markedly the air capacity. It resulted in a decrease of easily available water and increase of hardly available water contents, but the proper irrigation management allowed minimising this inconvenience.