Effect of Peat-based Container Media on Establishment of Scots Pine, Norway Spruce and Silver Birch Seedlings after Transplanting in Contrasting Water Conditions

Container seedlings were grown in pure sphagnum peat and peat mixtures containing coarse perlite and/or fine sand 25% by volume. Soil - water availability and rooting of the seedlings into the surrounding sandy soil after transplanting were studied in contrasting soil-water conditions in a greenhouse and a field experiment. No clear benefit was found for seedling rooting and establishment after planting by adding the used constituents to peat container medium. In fact, rooting of pine and birch was greatest in pure peat medium. Weakened seedlings occurred most frequently in media containing fine sand with lower water retention (in the matric potential range –1 to –10 kPa) than in pure peat or peat containing perlite. Preplanting and postplanting waterings clearly affected soil-water relations and seedling performance. Wet container media were found to release the most easily retained water into the soil within hours after planting. The amount of water released into coarse planting soil was less than that released into fine soil. Dry container media absorbed water from the soil for several days after planting, but still remained drier for a few days than those watered prior to planting. Preplanting watering decreased the mortality of conifer seedlings, and promoted their rooting into the soil, height growth and needle mass, but did not do so for birch. Postplanting watering did not affect mortality, but it promoted height growth and needle and leaf mass of all three species and rooting of birch. The results emphasize the importance of the water - retention characteristics of container media and of watering seedlings before outplanting for seedling establishment, especially in dry growth conditions.