The Effect of Light Quality and Fertility on Long Term Interior Maintenance of Selected Foliage Plants

Ficus benjamina, F. stricta, Dieffenbachia amoena and Brassaia arboricola were used to determine the effects of light quality and fertility on long-term maintenance of foliage plants in low light. The following light regimes were tested to determine the effect of light quality: 1) 100% PAR (photosynthetically active radiation) from fluorescent, 2) 70% PAR from fluorescent plus 30% PAR from incandescent, and 3) 50% PAR from each of Gro-Lux and Gro-Lux Wide Spectrum fluorescent. All light intensities were standardized at a total of 20 uEm⁻²s⁻¹ (149 ft-c) for 4 months then 14 uEm⁻²s⁻¹ (104 ft-c) for 8 months. When total PAR was equalized between treatments, no light source consistently proved superior for maintenance of the plants for one year in the interior. Three fertilizer regimes were used to maintain the four species in the interior for three months at 20 uEm⁻²s⁻¹ (149 ft-c) then for 9 months at 12 uEm⁻²s⁻¹ (89 ft-c). The fertilizer regimes tested were 1) soluble fertilizer (Peter's 20-20-20) added wkly in the irrigation water weekly at 200 ppm N : 88 ppm P : 166 ppm K, 2) slow-release fertilizer (Osmocote 14-14-14, 3 month release) applied as a top dress every three months at 4.1 g/15 cm (6 in) pot (0.57 g N : 0.25 g P : 0.47 g K), and 3) an unfertilized control. At the end of one year the effects of fertilizer treatment were found to be minimal, with the soluble fertilizer treatment showing some improved response with several growth parameters.