Peat Substrates Amended with Composted Bark or with Compost

Composted bark and composts are the most readily available alternatives to peat for production of growing media in the Czech Republic. In laboratory tests and in greenhouse experiments with pot plants (Chrysanthemum, Impatiens) nine substrate mixtures were compared: three peat substrates made from different types of blonde peat, three peat-bark substrates (20% vol. of composted bark), and three peat substrates with compost (10% vol. of compost). Chemical properties of the components and the substrates were analysed according to European Standards. Retention curves and other physical properties were measured on a sand box in the range of -0.25 to -10 kPa. At the end of the experiments the plants were evaluated for fresh weight, dry weight, and dimensions. Leaf content of macronutrients and micronutrients was measured too. Composition of the substrates (peat type, bark or compost amendment) affected shape of retention curves and other physical properties (bulk density, air pore space, proportion of available water). Doses of fertilizer and limestone were applied in relation to the chemical properties of the constituents. Compost-amended substrates had very high available potassium content. The content of available micronutrients was greatly influenced by bark or compost amendment but had no impact on their content in chrysanthemum and impatiens leaves. The highest plant dimensions, fresh weight, and dry weight were recorded in pure peat substrates but smaller size and more compact habit of chrysanthemum in bark-amended and compost-amended substrates meant better marketable quality. Individual peat types differed little in their effect on plant growth.