MAGNESIA, GREECE—To grow the high-quality potted plants preferred by consumers, many growers use chemical "regulators" designed to affect plant growth and development. The use of chemical growth retardants is standard practice in the production of compact gardenia plants; the chemicals are used to reduce plants' internode length, and encourage the production of lateral shoots that create aesthetically pleasing, spherical plants with plentiful flower buds. Chemical sprays are effective at reducing gardenia plant height, but need to be applied regularly—a practice that increases the cost of production and contributes to environmental pollution.
Dr. Constantinos Kittas and his colleagues from the University of Thessaly School of Agricultural Sciences and the Agricultural University of Athens (Greece) published a study in HortScience in which they report on experiments with the use of a photoselective polyethylene greenhouse covering film±a less expensive and more environmentally friendly alternative to chemical treatment—for production of compact potted gardenia (Gardenia jasminoides Ellis) plants.
Two types of experiments were performed on gardenia cuttings rooted in rooting benches and on young potted plants grown under low tunnels. In both experiments, two types of cover materials were used: a photoselective polyethylene (P-PE), filtering light within the wavelength range 600 to 750 nm and a common polyethylene film (C-PE) routinely used in greenhouse practice. The experiments were carried out in a commercial plastic-covered greenhouse located on the coastal area of eastern Greece.
The researchers recorded photosynthetically active radiation, cover materials' spectral properties, air temperature, and relative humidity inside the rooting benches and under the low tunnels. Plant growth indicators (including main shoot length and leaf area and lateral shoot number, leaf area, and fresh and dry weight) were determined along the growth cycle.
According to Kittas, "The research revealed that photoselective plastic films with high values and high B:R ratios are able to reduce the height of gardenia plants. However, continued development of gardenia plants under a P-PE film results in unmarketable, low-quality plants without lateral shoots and a resulting low number of flowers."
Although the study determined that the use of photoselective plastic films for the production of potted compact gardenia plants can contribute to the reduction of chemical use, Kittas added that more information about the effect of light quality and quantity as well as the necessary period of treatment on gardenia cuttings and transplanted plants is needed before this technology is used in commercial greenhouses for compact potted gardenia plant production.