PERFORMING INSTITUTION:
HORTICULTURE
CLEMSON UNIVERSITY
CLEMSON, SOUTH CAROLINA 29634

LIGHT MANAGEMENT STRATEGIES FOR COMMERCIAL GREENHOUSE PRODUCTION

OBJECTIVES: 1. To develop strategies to manage the light environment in greenhouses using retractable shade curtains. 2. To determine the impact of hanging basket production on the greenhouse light environment. 3. To quantify floricultural crop responses to light.

APPROACH: Despite the importance of light to the commercial production of floricultural crops, our understanding of the greenhouse light environment and floricultural crop responses to light is quite limited. Growers have empirically learned how to avoid obvious problems associated with extreme light conditions, but we are far from optimally utilizing light in commercial greenhouse production. This project will focus on identifying strategies for managing light levels inside greenhouses. First, we will explore methods for controlling retractable shade curtains. Retractable shade curtains have become a popular addition to many new greenhouses. The primary function of the retractable shade curtain is to provide higher light levels than permanent shade curtains while still allowing for shading during high temperatures and/or high light intensities. Neither the curtain manufacturers nor greenhouse growers fully understand how to use this new technology to deliver the optimal temperature and light environment, so our goal is to develop an understanding of how retractable shade curtains should be managed to provide the optimal greenhouse environment for crop production. The second focus will be on determining the impact of hanging baskets on the greenhouse light environment. Hanging baskets are grown under the trusses of most commercial greenhouse to optimize the use of greenhouse space. These baskets intercept light, and the foliage can alter the light spectrum, specifically the phytochrome photoequilibrium. Therefore, hanging baskets can alter both the light quantity and the light quality delivered to the crops growing below the baskets. Factors such as basket density, arrangement, color and plant size will influence the degree to which baskets affect the greenhouse light environment. Our goal is to quantify the effect of hanging basket production on the greenhouse light environment, which would allow commercial growers to optimize their space utilization efficiency by growing the maximum number of hanging baskets without reducing the bench crop quality. Finally, we must understand how light influences plant growth and quality to determine how to deliver the desired light environment. Very little specific information is available about the minimum or maximum light quantity requirements for most floricultural crops. Our goal is to quantify the light quantity responses of a wide range of floriculture crops.

NON-TECHNICAL SUMMARY: Light is frequently a factor limiting crop production in commercial greenhouses. Recently developed technologies allow growers to manipulate light with retractable shade curtains. However, strategies for managing retractable shade curtains inside commercial greenhouse do not exist. This project will focus on identifying strategies for optimizing the delivery of light to crops grown in commercial greenhouses.

PROGRESS: 2002/01 TO 2002/12
In 2002, we continued to conducted experiments to improve our understanding of how light should be managed in a commercial greenhouse. The primary foci have been to identify the light responses of numerous bedding plant species, to determine the effect of hanging baskets on the greenhouse light environment, and to develop best management practices for operating retractable shade curtain systems. Since light distribution is highly variable in greenhouses due to the style and orientation of the greenhouse, the time of year (latitude) and local climate, we have begun to move towards modeling light distribution and plant responses in order to more effectively extrapolate our lab results to the U.S. commercial greenhouse industry. A M.S. student, Veronda Holcombe, finished her thesis in 2002. Her project examined the responses of various bedding plant species to the daily light integral. This information is useful for determining the best practices for managing retractable shade curtains and for determining the maximum number of hanging baskets that can be grown in a commercial greenhouse, while minimizing the negative impact on the crops grown below the hanging baskets. This information is very useful for increasing greenhouse profitability, so Dr. Faust has been asked to speak at numerous conferences on this topic (see Expected Impact section below). A model is being developed to estimate the effect of hanging baskets on light distribution in commercial greenhouses. An experiment was conducted at a commercial greenhouse facility in SC to provide data for validation of the current working model. A software program, WinScanopy, is being used to analyze light interception by hanging baskets. This software uses digital fish-eye lens images to determine the shadow patterns created by hanging baskets. A series of experiments was conducted with the gas exchange chambers (described in previous reports) to determine the photosynthesis response curves for a range of bedding plant species. These curves are used to predict the response of these species to retractable shade curtains. A model is being developed to predict the effect of different retractable shade management techniques on plant growth and flowering. A Ph.D. student, Joaquin Chong, started in May. His project involves modeling poinsettia stock plant responses to light and temperature. The model will be used to predict cutting yields and to predict the result of using different stock plant management techniques to optimize production efficiency. The initial experiment was conducted during the fall. The preliminary results suggest that temperature is the primary factor affecting the rate of node formation, while light is the primary factor determining the number of shoots that develop per unit area. Each shoot in the canopy develops nodes at different rates depending on the position of the shoot.

IMPACT: 2002/01 TO 2002/12
In 2002, Dr Faust was invited to present the results of his light research in CA, MI, MA, VA, OH & Canada. Dr Faust wrote the Light chpt for the Ball RedBook and has been asked to write book chpts on light in 2 books to published in 2003 & 04. Dr Faust was approached by 3 Gh businesses to conduct research to solve different production-related issues. Dr Faust was contacted because of his expertise in the area of light, since the problems were initially thought to be light-related. A large international supplier of poinsettia cuttings was having severe problems shipping their cuttings internationally. The cuttings would defoliate shortly after being received by the wholesale grower. Expts demonstrated a clear relationship between tissue nutrient concentration and post-harvest performance. A large national supplier of pansy plugs was having severe problems with shoot-tip abortion. The problem primarily occurs during July and August, so excessive light was considered to be a possible cause. Expts demonstrated that shoot-tip abortion is directly related to the amount of water applied via misting. The problem occurs during the summer because mist frequency increases due to the higher solar radiation load and warmer temps. One of the largest producers of Exacum was having consistent production losses due to the inadequate crop height. The literature describes Exacum as a dayneutral species; however, our results clearly show that Exacum is a facultative long day crop. Thus, short days can be provided to delay flowering and consequently increase plant height at the time of flower.

PUBLICATIONS: 2002/01 TO 2002/12
1. Faust, James E., Light. In: Ball RedBook, 17th ed., D. Hamrick (ed.), Ball Publishing, Chicago IL (to be published in 2003)
2. Faust, James E., Hanging basket production and profitability. In: Tips on Greenhouse Profitability, P. Konjoian and James E. Faust (eds.), Ohio Florists' Assoc., Columbus, OH (to be published in July 2004)
3. Bunnell, B.T., L.B. McCarty, W.C. Bridges, J.E. Faust and N.C. Rajapakse. 2002. Daily sunlight requirements for TifEagle bermudagrass golf greens. ASA Annual Meeting Abstracts 94: In press.
4. Korczynski, Pamela C., Joanne Logan and James E. Faust. 2002. Mapping the monthly distribution of the daily light integral across the contiguous United States. HortTech. 12(1):12-15.
5. Holcombe, Veronda and James E. Faust. 2002. Quantifying the effect of daily light integral on bedding plants. Masters Thesis

PROJECT CONTACT:

Name: Faust, J. E.
Phone: 864-656-4966
Fax: 864-656-4960
Email: jfaust@clemson.edu