Two complementary studies examining petunia propagation practices reveal that precise manipulation of light intensity and temperature conditions plays a critical role in producing high-quality plants. Together, the findings offer actionable insights for growers seeking to refine propagation protocols and maximize crop uniformity and aesthetic appeal.
The first study demonstrates that increasing LED supplemental light intensity and implementing root zone heating both contribute to improved plant morphology and enhanced leaf coloration during the rooting stage. Higher light levels were associated with more compact, robust growth and increased anthocyanin concentrations, which contribute to deeper pigmentation in foliage. In contrast, the inclusion of far-red light showed minimal impact on these parameters, suggesting it may be unnecessary in propagation-specific lighting strategies.
The second study focuses on the interaction between air temperature management and supplemental lighting during propagation. Results indicate that carefully controlled temperature regimes, when paired with appropriate lighting strategies, significantly influence plant growth and structural development. Warmer root-zone conditions and optimized air temperatures rooting prevented the development of discolored foliage
and improved overall plant quality, while suboptimal conditions led to delayed development and less desirable morphology.
Taken together, the studies underscore the importance of integrating both light and temperature management to achieve consistent and high-quality petunia propagation. Growers can improve outcomes by prioritizing higher light intensities and maintaining favorable thermal conditions, particularly in the root zone, while avoiding unnecessary energy expenditures on far-red lighting that does not contribute measurable benefits during this stage.
These findings provide a clearer framework for greenhouse producers aiming to enhance efficiency, reduce input costs, and deliver superior ornamental crops to market.
According to Mr. Smith, he was prompted to conduct the research after Drs. Lopez and Smith were discussing potential issues with light emitting diodes (LEDs) as supplemental lighting. "Both Lopez and Jahnke noticed that some bedding plant species, such as petunia, became purple when propagated from unrooted cuttings underneath LEDs. This observation was supported by reports from greenhouse growers that also noted the development of purple leaves in cuttings rooted under LEDs.
This research was conducted by Charlie Smith during his M.S. studies at Michigan State University. Now a Ph.D. student, Smith worked with advisors Roberto Lopez and Erik Runkle on experimental design, data analysis, and manuscript preparation. Nathan Jahnke of Ball Horticultural Company contributed to the experimental design and helped identify the purpling issue, while Kellie Walters of University of Tennessee assisted with sample processing and data analysis.
The full articles can be read on the ASHS HortScience electronic Journal website at:
+https://doi.org/10.21273/HORTSCI18797-25 and https://doi.org/10.21273/HORTSCI18965-25
Established in 1903, the American Society for Horticultural Science is recognized around the world as one of the most respected and influential professional societies for horticultural scientists. ASHS is committed to promoting and encouraging national and international interest in scientific research and education in all branches of horticulture.
Comprised of thousands of members worldwide, ASHS represents a broad cross-section of the horticultural community - scientists, educators, students, landscape and turf managers, government, extension agents and industry professionals. ASHS members focus on practices and problems in horticulture: breeding, propagation, production and management, harvesting, handling and storage, processing, marketing and use of horticultural plants and products. To learn more, visit ashs.org.
