GROWTH OF DIEFFENBACHIA-MACULATA CAMILLE IN GROWING MEDIA CONTAINING SPHAGNUM PEAT OR COCONUT COIR DUST

A comparison was made of Canadian sphagnum peat (SP) and Philippine co conut (Cocos nucifera L.) coir dust (CD) as growing media components f or Dieffenbachia maculata [(Lodd.) G. Don] 'Camille' greenhouse produc tion, Three soilless foliage plant growing mixes [Cornell, Hybrid, Uni v. of Florida #2 (UF-2)] were prepared using either SP or CD and pine bark (PB), vermiculite (V), and/or perlite (P) in the following ratios (percent by volume): Cornell = 50 CD or SP:25 V:25 P, Hybrid = 40 CD or SP:30 V:30 PB, UF-2 = 50 CD or SP:50 PB, Initial Cl concentrations and electrical conductivities were higher for CD-containing media (CDM ) than SP-containing media (SPR;I). At termination, Ca, Mg, and NO3-N concentrations were higher for SPM than CDM, Bulk densities were lower for CDM than SPM for one medium, but not for the others. Water-filled pore space (W-FPS) and water-holding capacity (W-HC) were larger and air-filled pore space (A-FPS) generally was smaller for CDM than SPM. Cornell had the highest W-FPS and W-HC, lowest A-FPS and percentage of large particles, and produced the highest grade and heaviest plants, Plant top grades, fresh mass and overall mass, but not root grades and mass, were higher for CDM than SPM, Plant mass was positively correla ted with initial medium W-HC but not with A-FPS. Lower K in mix UF-2 c ompared to the mixes containing vermiculite may have been partly respo nsible for the lesser growth in that mix.