Influence of Light Duration and Fertilization on Indoor Plant Quality

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University of Florida, IFAS
Central Florida Research and Education Center - Apopka
CFREC-Apopka Research Report RH-91-15

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

Light levels and fertilizer application rates are important factors influencing the quality of foliage plants maintained in interior environments. Recommended fertilizer application rates for foliage maintained indoors vary depending on genera and interior light intensity. Foliage plants maintained in low light interiors (100 ft-c or less) grow slowly and use little fertilizer because the rate at which they perform metabolic activities necessary to manufacture food is slower. Since plants continue to manufacture food when light is present, they are often illuminated for longer periods when maintained indoors under low light, which may help counteract effects of lower than recommended illumination levels as long as they are above the light compensation point. The following experiment was conducted to study effects of indoor light duration and fertilizer rate on quality of foliage plants maintained in an interior environment.

Methods

This 3 x 3 factorial experiment, with 5 replications, utilized good quality finished Aglaonema 'Silver Queen' ('Silver Queen' aglaonema), Chamaedorea elegans (parlor palm), Codiaeum variegatum 'Petra' ('Petra' Croton) and Dieffenbachia maculata 'Camille' ('Camille' dieffenbachia). Plants were grown in 6 inch containers in central Florida, using production regimes designed to produce acclimatized foliage. Research began on 18 January 1991, when plants were placed in rooms where they received 100 ft-c from cool white fluorescent lamps for 8, 12 or 16 hours per day. Temperatures in the rooms ranged from 70 to 80°F and plants were watered once or twice a week as needed. Plants received no fertilizer, or were fertilized with 1 or 2 g/6 inch pot 19-6-12 Osmocote 3 month release rate fertilizer (Grace/Sierra Co., Milpitas, CA 95035), applied on 30 January and 9 May 1991. Rates tested (0, 1 and 2 g/6 inch pot), were equivalent to 0, 3.75 and 7.5 g/N/ft²/yr, respectively.

Plant height was measured on 24 January 1991, 29 April and 19 July 1991. Plant grades for all three plants were determined on 11 April and 19 July 1991, based on a scale of 1 = poor quality, unsalable, 3 = fair quality, salable and 5 = excellent quality. Electrical conductivity (µmhos/cm) of the leachate collected from medium in pots containing parlor palms was measured using the pour-though method, on 29 January, 9 May and 22 July 1991, the day the study was terminated.

Results

Six months after placement in rooms, only plant grades of 'Camille' dieffenbachia showed differences between plants exposed to 100 ft-c for 8, 12 or 16 hours per day (Table 1). 'Camille' dieffenbachia plant grade increased slightly as light duration increased and best quality plants were maintained with 16 hours of light daily. However, 'Camille' dieffenbachia plant quality was lower after six months indoors compared to the other plants tested; even plants receiving light only 8 hours per day. Fertilization rate did not affect grades of any plants used in this test.

Parlor palms and 'Petra' crotons were the only two plants whose increase in height after six months in rooms was influenced by light duration (Table 2). Both grew taller as daily exposure time to the light level of 100 ft-c increased. 'Petra' crotons were the only plants whose increase in height while in the rooms was affected by fertilizer rate. Plants receiving no fertilizer were taller than plants fertilized with the l or 2 g/6 inch pot rates. Electrical conductivity (µmhos/cm) of the leachate from pots containing parlor palms also increased with fertilization level, when measured after plants were maintained in rooms for three and six months (Table 3). Leachate pH increased with all fertilizer treatments, but were higher in the pots receiving no fertilizer or the low rate of fertilizer than in the pots getting the high fertilizer treatment.

Conclusions

The current light level and fertilizer rate recommendations for Dieffenbachia species maintained in interior environments specify a minimum of 150 ft-c and 4g/N/ft²/yr. Even though 'Camille' dieffenbachias received somewhat higher plant grades as daily exposure time to 100 ft-c increased, the increase in light duration did not fully compensate for lower than recommended light intensity. Dieffenbachia need higher light and fertilizer levels when maintained in interior environments than those provided in this test. Interior maintenance recommendations for croton cultivars are 150 ft-c minimum light intensity and 2 g/N/ft²/yr. 'Petra' crotons maintained good quality under the lower than recommended light levels utilized in this experiment, and did grow slightly taller as light duration increased or fertilizer level decreased. 'Silver Queen' aglaonema and parlor palm were grown at higher than the minimum recommended light and fertilizer levels of 75 ft-c and 2 g/N/ft²/yr and all plants maintained good quality regardless of lighting duration or fertilization rate.

Plants grow slowly and use little fertilizer when maintained under low light levels. When fertilizer rates are too high, excess ions accumulate in the growing medium and may eventually cause injury to roots. The medium leachate from pots receiving high rates of fertilizer had the highest level of electrical conductivity and lower pH after several months, indicating accumulation of fertilizer ions compared to pots receiving less fertilizer. Parlor palms maintained under the low light conditions of this test did not utilize the extra fertilizer ions available when treated with the high rate of fertilizer.

*Professor, Plant Physiology, and Professor of Environmental Horticulture and Center-Director, respectively. Central Florida Research and Education Center - Apopka, 2807 Binion Road, Apopka, FL 32703-8504.

Additional Reading

1. 1. Conover, C.A. and R.T. Poole. 1991. Light and fertilizer recommendations for indoor maintenance of acclimatized plants. Univ. of Fla., IFAS, CFREC-Apopka Res. Rpt. RH-91-7.

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

   3. Conover, C.A., R.T. Poole and T.A. Nell. 1982. Influence of intensity and duration of cool white fluorescent lighting and fertilizer on growth and quality of foliage plants. J. Amer. Soc. Hort. Sci. 107(5):817-822.

   4. Manaker, G.H. 1981. Light. p.66-68. In: Interior Plantscapes, Prentice-Hall, Englewood Cliffs, N.J.

   5. Turner, M.A., D.L. Morgan and D. Wm. 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.

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

1. Table 1. Plant grades^Z of foliage plants maintained in rooms with various lighting regimes from 18 January until 19 July 1991.

1. ^ZPlants were graded on a scale of 1 = poor quality, unsalable, 3 = fair quality, salable and 5 = excellent quality on 19 July 1991. Experiment terminated on 22 July 1991.
   ^YPlants received 100 ft-c light from cool white fluorescent bulbs 8, 12 or 16 hours per day.
   ^Xns or **; Results nonsignificant or significant at P = 0.01.

1. Table 2. Height change (cm) of foliage plants maintained in rooms with various lighting and fertilizer regimes from 18 January until 19 July 1991.^Z

1. ^ZPlant height was measured on 24 January and 19 July 1991. Height change = 19 July height - 24 January height. Experiment terminated on 22 July 1991.
   ^YPlants received 100 ft-c light from cool white fluorescent bulbs for 8, 12 or 16 hours per day.
   ^Xns or *; Results nonsignificant or significant at P = 0.05.
   ^WOsmocote 19-6-12 3 month release rate fertilizer applied 30 January and 9 May 1991. Rates tested (0, 1, and 2 g/6" pot), were equivalent to 0, 3.75 and 7.5 g/N/ft²/yr, respectively.

1. Table 3. Electrical conductivity (µmhos/cm) and pH of leachate from pots containing Chamaedorea elegans maintained in rooms with various fertilizer rates from 18 January until 22 July 1991.

1. ^Z19-6-12 Osmocote 3 month release rate fertilizer applied 30 January and 9 May 1991. Rates tested (0, 1, and 2 g/6" pot), were equivalent to 0, 3.75 and 7.5 g/N/ft²/yr, respectively.
   ^Yns, * or **; Results nonsignificant or significant at P = 0.05 or P = 0.01, respectively.