Effects of Light Intensity and Fertilizer Formulation
on Six Foliage Plants Growing Indoors

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R. T. Poole and C. A. Conover*

University of Florida, IFAS
Central Florida Research and Education Center - Apopka
CFREC-Research Report, RH-90-16

Ideally, foliage plants in the interior environment should maintain original quality and grow slowly. Interiorscapers need to know if fertilizer formulation affects indoor plant maintenance and also if fertilizer formulations should change as light intensities increase or decrease. The following experiment, initiated July 20, 1989, examined the effects of fertilizer formulation on six species of foliage plants maintained under three light intensities in rooms simulating an interior environment.

All plant material utilized were finished, ready for sale plants, growing in six inch pots, obtained from commercial growers and included; Aglaonema 'Silver Queen' (Silver Queen aglaonema), Alpinia variegata (Shell ginger), Chamaedorea elegans (Parlor palm), Codiaeum variegatum 'Petra' (Petra croton), Dracaena fragrans 'Massangeana' (Striped corn plant), and Nephrolepis exaltata 'Dallas' (Dallas fern). Plants were placed in rooms receiving 75, 150 or 225 ft-c light, 12 hours daily, from cool white fluorescent bulbs. Temperature ranged from 70 to 80°F and plants were irrigated 1 to 2 times a week as needed. Fertilizer treatments included applying 2 grams per pot 19-6-12 Osmocote or 2.7 grams per pot 14-14-14 Osmocote. Osmocote is manufactured by Sierra Chemical Co., Milpitas, CA. Both fertilizers have three month-release durations and were applied initially July 20 and again on October 20. Therefore, all plants received the same amount of nitrogen, the most influential element in foliage plant growth. Soluble salts were measured July 26, October 30, and January 18 using the pour-through method. Height was measured initially July 26 and again October 12 and January 18. Plants were graded on a scale of 1=poor, unsalable; 3=average, salable and 5=excellent quality. On September 26, (Ca(OH)₂ (calcium hydroxide) 1 tsp/L solution was applied 100 ml/pot to the Chamaedorea elegans to correct acidic pH.

Plants receiving higher light intensities were taller at termination of the experiment than plants maintained under the lower light intensities, except for Aglaonema 'Silver Queen' (Table 1). Plant grade of Alpinia variegata and Chamaedorea elegans receiving 75 ft-c was higher January 18, 1990 than October 30, 1989, but grades of other cultivars maintained under 75 ft-c were lower at 6 months than at 3 months. Plant grade after 6 months was highest for plants maintained under 225 ft-c. These plants showed the most improvement in quality or the least amount of deterioration after 6 months (Table 2).

Soluble salts levels of the leachate usually decreased with time and were lower at 225 ft-c. Plants grew more, thus utilized more fertilizer at 225 ft-c than at the lower light levels tested. These two factors account for electrical conductivity of pots decreasing as light levels increased (Table 3).

Fertilizer formulation had no effect on soluble salts levels, plant growth or grade. Fertilizer formulation did have a significant effect on amount of phosphorus and potassium found in leachate of Codiaeum variegatum 'Petra'. Leachate from pots containing plants receiving 14-14-14 contained over twice as much phosphorus as leachate collected from pots with plants receiving 19-6-12 (Table 4). Since plants used less fertilizer at lower light levels, fertilizer application rates can be reduced when plants are maintained in a low light intensity environment to save money and reduce pollution of the environment.
Since formulation had no effect on plant growth, a ratio of 3:1:2 (N-P₂0₅-K₂O) should be used instead of fertilizers with P and K equal to N (1-1-1) or higher than N (1-3-2) to minimize pollution from phosphates and potash.
Of the plants tested, Aglaonema 'Silver Queen' and Chamaedorea elegans appear to maintain best quality when subjected to low light intensities for prolonged periods.

1. *professor of Plant Physiology, and Professor and Center Director, respectively. Central Florida Research and Education Center - Apopka, 2807 Binion Rd., Apopka, FL 32703-8504

Additional Reading

1. 1. Poole, R T. and A. R Chase. 1987. Response of foliage plants to fertilizer application rates and associated leachate conductivity. HortScience 22(2):317-318.

   2. Conover, C. A. and R T. Poole. 1984. Acclimatization of indoor foliage plants.Horticultural Review 6:119-154.

   3. Conover, C. A. and R T. Poole. 1981. Influence of light and fertilizer level and fertilizer sources on foliage plants maintained under environments for one year. J. Amer. Soc. Hort. Sci. 106(5):571-574.

   4. Turner, M. A., D. L. Morgan and D. W. Reed. 1987. The effect of light quality and fertility on long term interior maintenance of selected foliage plants. J. Environ. Hort. 5(2):76-79.

   5. Wright, R D. 1986. The pour-through nutrient extraction procedure. HortScience 21:227-229.

Table 1. cont.

1. ^Z19-6-12 three month release rate Osmocote was applied 2 grams/pot July 20 and October 20.
   ^Y14-14-14 three month release rate Osmocote was applied 2.7 grams/pot July 20 and October 20.
   ^Xns and **; Nonsignificant and significant at the 5% level.