Growth of Gardenia jasminoides 'Veitchii' Under Red or Black Shadecloth

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University of Florida, IFAS,
Central Florida Research and Education Center - Apopka
CFREC - Apopka Research Report RH-92-7

R.T. Poole, R.H. Henley and K. Steinkamp*

SADH, (Butanedioic acid, mono (2, 2-dimethylhydrazide), is the active ingredient in the growth retardants B-Nine® and Alar 85®, used to slow cell division and elongation, and also to induce flowering. These widely used growth retardants minimize internodal elongation without reducing number of nodes, thereby producing more compact plants. Growth retardation, primarily through chemical means, is expensive and growers seek to limit their use in order to maximize profits.

Light quality also affects plant cell elongation. Light is composed of waves of different lengths and the term "quality" is used when examining the ratios of the various wavelengths in a light source. A combination of red and blue wavelengths control photosynthesis. Plant elongation is controlled by the wavelength ratios in the light they receive. Blue wavelength light produces compact, lateral branching, dark green plants while light predominately from a far-red source produces stem elongation and etiolated weak plants. Indoor blue:red wavelength ratios are controlled by manipulating lighting source, but it is much more difficult to affect a wavelength ratio change under commercial production regimes. Red shadecloth absorbs blue light, and theoretically could change the red:blue spectrum plants receive. The following research was conducted to study the effects of shadecloth color on light quality and plant growth.

Materials and Methods

A 2 x 2 factorial experiment with 15 plants per treatment, initiated on 5 September 1991, was conducted at a production nursery in Plymouth, Florida. Six-inch containers of "pre-finished" Gardenia jasminoides 'Veitchii' (gardenia), approximately 16 inches tall, that had been pruned back in August and were ready for floral induction, were placed in a shade house where temperatures ranged from 45 to 95°F. Plants were placed under 30% shadecloth (Weathashade Corp., Apopka, FL 32703) of either black or red color and watered as needed to maintain healthy growth. Alar 85® (Uniroyal Chemical, Bethany, CN 06525) was applied to gardenias under each of the 2 shadecloth colors in order to control growth and induce flowering. Alar 85®, at the rate of lb active ingredient to 20 gal water (3000 ppm), was sprayed on foliage until the drip point was reached, whenever internodes started to elongate. Gardenias were treated with Alar 85® 3 times during production, at approximately monthly intervals, starting 26 September and ending 26 November 1991

Light quality was measured monthly between 1 and 2 p.m. using a plant growth photometer (IL 150, International Light Inc., Newburyport, MA 01950), which measured irradiance of the blue (400-500 nanometers [nm]), red (600-700 nm) and far-red (700-800 nm) wavelengths in, µwatts/cm2-nm. Light measurements were taken 5 September, 17 October and 16 December, 1991. Gardenia height was measured monthly 12 September, 17 October, 29 November and 16 December 1991. Number of blooms per plant was also counted 16 December.

Results and Discussion

The radiant energy from the blue, red and far-red portions of the spectrum measured by the photometer varied according to shadecloth color (Table 1). Because plants under different colored cloth received different amounts of blue, red and far-red wavelengths, ratios also varied according to cloth color (Table 2). Gardenias under red shadecloth received more light from the red region of the spectrum than the blue region. The light also had a higher far-red:red ratio compared to plants under the black shadecloth, which received a higher percentage of light from the blue region of the spectrum and had a higher blue:red ratio compared to the plants under the red cloth. This could explain why plants under the red shadecloth were taller than plants grown under blue shadecloth (Table 3).

An interaction between growth regulator use and shadecloth color affected plant height. Gardenias grown under the black cloth not treated with the growth retardant were shorter than non-treated plants grown under red cloth (Table 3). However, Alar 85® suppressed growth of plants under both cloth colors equally, and only plants receiving growth regulators were ready for sale when this experiment was terminated.

Shadecloth color did not influence number of blooms per plant, but blooming was greatly affected by growth regulator treatment (Table 2). Plants sprayed with Alar 85® were blooming and salable, while those not sprayed showed excessive internode elongation and incomplete flower initiation.

*professor of Plant Physiology, Professor of Environmental Horticulture and Technical Assistant, respectively, IFAS, CFREC-Apopka, 2807 Binion Road, Apopka, FL 32703-8504.

  1. Table 1. Light intensity of blue, red and far-red wavelengths, measured 1-2 p.m. at plant level, after filtering through black or red shadecloth on 5 September, 17 October and 16 December 1991.
  Measured wavelengths
filtered through
red shadeclothz
Measured wavelengths
filtered through
black shadecloth
Date Blue Red Far-red Blue Red Far-red
5 September 30 32 30 41 34 30
17 October 44 46 44 52 43 40
16 December 44 51 56 61 64 62
  1. zintensity of blue (400-500 nanometers [nm]), red (600-700 nm) and far-red 700-800 nm) wavelengths was measured in microwatts/cm2-nm with a photometer (IL 150, International Light Inc., Newburyport, MA 01950).

  1. Table 2. Blue:red and Red:far-red ratios in light, filtered through red or black shadecloth on 5 September, 17 October and 16 December 1991. Wavelengths measured at plant level.
  Wavelength ratios of light
filtered through
red shadeclothz
Wavelength ratios of light
filtered through
black shadecloth
Date Blue:Red Red:Far-red Far-red:red Blue:red Red:Far-red Far-red:red
5 September 0.94 1.06 0.94 1.21 1.13 0.88
17 October 0.96 1.05 0.95 1.21 1.08 0.92
16 December 0.86 0.91 1.09 0.95 1.03 0.97
  1. zIntensity of blue (400-500 nanometers [nm]), red (600-700 nm) and far-red 700-800 nm) wavelengths was measured in microwatts/cm2-nm with a photometer (IL 150, International Light Inc., Newburyport, MA 01950).

  1. Table 3. Effects of shadecloth color and Alar 85® on height (cm) and number of blooms on 16 December 1991, of Gardenia jasminoides 'Veitchii' grown under 30% red or black shadecloth from 5 September until 16 December 1991. Plants received either 3 Alar 85® treatments or were not treated with growth regulator. Initial plant height, measured on 12 September, averaged 16 cm.
Shadecloth color Growth regulator Final height (cm) No. of blooms
Black None 33b 0.3a
Black Alar 85® 22a 6.7b
Red None 38c 0.0c
Red Alar 85® 22a 6.1b
  1. z Mean separation in columns by Duncan's multiple range, 5% level.

Additional Reading

  1. 1. Barnes, C. and B. Bugbee. 1992 Morphological response of wheat to blue light. J. Plant Physiol.. 139: 339-342.

    2. Bickford, E.D. and S. Dunn. 1972. Photoperiodism and photomorphogensis. Chapter in:Lighting for Plant Growth. Kent State Univ. Press. pp 81-99.

    3. Corth, R. 1974. Lighting for plant growth. Florist 7(9):48-50.

    4. Gaines, R.L. 1977. Light - a major requirement for plant survival. Chapter in: Interior Plantscaping. McGraw-Hill, New York, NY.

    5. McConnell, D.B. and R.T. Poole. 1981. Growth regulators. Chapter in: Foliage Plant Production, J.N. Joiner, ed. Englewood Cliffs, NJ. pp. 313-319.

    6. Rajapakse, N.C. and J.W. Kelly. 1991. Influence of CuSO4 spectral filters, daminozide and exogenous gibberellic acid on growth of Dendranthema X grandiforum (Ramat.) Kitamura 'Bright Golden Anne'. J. Plant Growth Regulator 10:207-214.