A comparison was made of Philippine coconut coir dust and Canadian spaghnum peat as components of three growing media for greenhouse production of Dieffenbachia maculata `Camille'. The soilless media were prepared using coir or peat in various amounts (by volume) combined with pine bark, vermiculite, and/or perlite (Media A–50% coir/peat: 25% vermiculite: 25% perlite; Media B–40% coir/peat: 30% vermiculite: 30% bark; Media C–50% coir/peat: 50% bark). Chemical and physical properties of the soils were determined at the beginning and the end of the five-month production cycle. Plant root and top growth and grades were determined at the end of the experiment. Initially, saturated media extracts from coir-containing media had elevated K, Cl, and soluble salts levels compared to peat-containing media; however, by the end of the experiment those levels were lower in coir- than in peat-based media. Water-filled pore space and water-holding capacities were generally higher and air-filled pore space lower in coir- than in peat-based media, probably due to differences in particle size distributions. There were no interaction effects on plant growth between growing media and coir versus peat. Plant root and top growth in Media A > Media B > Media C and plant top growth was greater in coir- than in peat-based media. Differences in growth could be due, in part, to differences in media water-holding capacities.
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