Study shines light on ways to cut costs for greenhouse growers

January 23, 2012

WEST LAFAYETTE, Ind. - Greenhouse bedding plant growers can save themselves time, money or possibly both by giving cuttings in propagation more light, according to a Purdue University study.

Flower growers use cuttings from Central America and Africa to start spring bedding plants in greenhouses during winter and early spring. Those cloudy days and cool temperatures make propagation time- and energy-intensive.

Roberto Lopez, an assistant professor of horticulture, and horticulture graduate students Chris Currey and Veronica Hutchinson study ways to minimize inputs and production costs in the floriculture industry while improving product quality. Based on what they were hearing from growers, they realized that light wasn't getting the attention it needed from the industry.

"In their minds, temperature has always been the most important thing. They didn't think about light," Lopez said. "We knew that light was significant, but we realize we didn't know what level to recommend."

Currey said growers were concerned that using too much light would stress the cuttings and disrupt root development.

"The dogma has been to keep light low, but that actually made the cuttings take longer to root," said Currey, whose findings were published in the January issue of the journal HortScience.

Currey, Hutchinson and Lopez propagated nine popular spring bedding plants under differing amounts of light for two weeks. They took a quality index used in forestry and modified it for bedding plants to assess the quality of the plants based on the light levels. They measured stem length, stem caliper, shoot dry mass and root dry mass.

Overall, plants rooted faster with more light and the plants were higher quality. Both factors could increase profits for greenhouse growers, Lopez said.

"With reduced production time, you can save on production costs or increase your crop production by starting another second crop that wouldn't have been possible with reduced light," Currey said. "That's increased profits through greenhouse space savings or energy savings, as well as through a higher quality product."

A copy of the paper, with more specific light requirements, can be viewed at https://sharepoint.agriculture.purdue.edu/agriculture/flowers/publications.aspx

Next, Lopez and Currey plan to study the morphological and physiological changes associated with light and cutting propagation, as well as how LED lights can be used to add supplemental daily light for cuttings.

The Fred C. Glockner Foundation, U.S. Department of Agriculture Specialty Crop Research Initiative and the Indiana Flower Growers Association funded this research.

Writer:  Brian Wallheimer, 765-496-2050, bwallhei@purdue.edu

Sources:  Roberto Lopez, 765-496-3425, rglopez@purdue.edu

                   Chris Currey, 765-496-3425, ccurrey@purdue.edu 

Ag Communications: (765) 494-2722;
Keith Robinson, robins89@purdue.edu
Agriculture News Page

ABSTRACT

Growth Morphology, and Quality of Rooted Cuttings of Several
Herbaceous Annual Bedding Plants Are Influenced by Photosynthetic
Daily Light Integral During Root Development

Christopher J. Currey, Veronica A. Hutchinson and Roberto G. Lopez

Cuttings of herbaceous annual bedding plants must be rooted in late winter and early spring when ambient outdoor photosynthetic daily light integrals (DLIs) are at seasonally low levels. We evaluated the effect of DLI during root development on growth, morphology, and quality of nine popular vegetatively propagated annual bedding plant species. Cuttings of Angelonia angustifolia Benth. 'AngelMist White Cloud,' Argyranthemum frutescens (L.) Sch. Bip. 'Madeira Cherry Red,' Diascia barberae Hook. f. 'Wink Coral,' Lantana camara L. 'Lucky Gold,' Nemesia fruticans (Thunb.) Benth. 'Aromatica Royal,' Osteospermum ecklonis (DC.) Norl. 'Voltage Yellow,' Scaevola L. hybrid 'Blue Print,' Sutera cordata Roth. 'Abunda Giant White,' and Verbena Ruiz hybrida 'Aztec Violet' were harvested and propagated in a glass-glazed greenhouse with 23 C air and substrate temperature set points. After callusing (≈5 molm−2d−1 for 7 days), cuttings of each species were placed under one of three different fixed-woven shade cloths providing ≈38%, 61%, or 86% shade or no shade with 16 h of supplemental light for 14 days. There were no clear trends across species for stem length in response to DLI. Stem caliper of Argyranthemum, Diascia, and Nemesia increased by 35%, 119%, and 89%, respectively, as DLI increased from 1.2 to 12.3 molm−2d−1. Depending on species, total, shoot, and root dry mass increased by 64% to 465%, 50% to 384%, and 156% to 1137%, respectively, as DLI increased from 1.2 to 12.3 molm−2d−1. The quality index, an objective, integrated, and quantitative measurement of rooted cutting quality, increased for all species by 176% to 858% as DLI increased from 1.2 to 12.3 molm−2d−1. Our results indicate that providing a DLI of ≈8 to 12 molm−2d−1 after callusing increases both growth and quality of rooted cuttings.