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Light Manipulation for Ornamental Crop Production

Light Manipulation for Ornamental Crop Production

Have you ever heard of an ornamental kale or pepper plant? Rather than being grown to eat, ornamentals are cherished for their aesthetic: displaying leaves, fruits, and flowers of interesting colors, shapes, and aromas (Figure 1). The most recent USDA census found the U.S. ornamental production industry worth $6.2 billion per year, with over 17,000 growers using glass or other controlled environments for their crops (USDA NASS, 2020).

These controlled environment growers manipulate light to alter plant shape, increase cutting quantity, and, in the case of flowering ornamentals, control flowering time, which allows for crop scheduling (Runkle and Heins, 2006). Greenhouse growers use various products to manipulate light, including shade/blackout cloths, exterior applied greenhouse coatings, and supplemental lighting.

Light Manipulation for Ornamental Crop ProductionLight Manipulation for Ornamental Crop ProductionLight Manipulation for Ornamental Crop Production

Figure 1. Bolivian rainbow pepper, medusa pepper, and ornamental kale showing eye-catching fruits and leaves.

To understand the applications of these different products, two adjustable characteristics of light are important to know: light quality and light quantity. Light quality pertains to the spectral wavelength composition of the light source; for example, sunlight quality at Earth’s surface is approximately 43% photosynthetically active radiation (PAR) (400-700nm) and 4% ultraviolet (UV) (300-400 nm) (NationalRenewable Energy Laboratory, n.d.).

PAR and UV light, as well as far-red (700-750 nm), contribute to plant growth and development and are called biologically active radiation (Zhen et Figure 1. Bolivian rainbow pepper, medusa pepper, and ornamental kale showing eye-catching fruits and leaves.al., 2021). PAR, however, is the most critical to plant growth because it contributes directly to photosynthesis. 

Light quantity is the amount of PAR light received, expressed as daily light integral, (DLI). Two variables contribute to DLI. One is instantaneous light intensity, or the number of PAR photons received during one second in a given area, expressed as photosynthetic photon flux density ,(PPFD). 

Second is the duration of light received during a day, called photoperiod. Photoperiod is crucial for plant development, most notably inducing flowers in many crops. Commercial growers primarily manipulate light quantity; however, other light characteristics (including quality) change. 

Decreasing PPFD – Shade Cloths

One reason ornamental growers reduce PPFD is to grow plants that naturally thrive in shadier environments, such as coleus, begonia, and impatiens. Shade cloths, called shade nets or screens, are commonly used to decrease PPFD. They contain materials that reflect or absorb light, resulting in more diffuse light that can penetrate deeper into the crop canopy (Shahak, 2006). 

This diffuse light provides side-lighting to hanging basket plants (Figure 2), which had total sales of $ 67.2 million in 2020 (USDA, 2020). Hanging baskets require even weight dispersion on all sides to avoid tipping, including evenly dispersed lighting to obtain the desired plant structure with light diffusion.

One of the most popular hanging basket ferns grown in controlled environments is the Boston fern. Seltsam and Owen (2022) used shade cloths to apply five different levels of DLI to identify an optimal range to grow the species. A DLI range of 10-12 mol m-2d-1 Figure 2. 

Production greenhouses are growing hanging baskets above rows to maximize their space use efficiency. They maximized the frond number in 7 of 11 cultivars. Based on height and diameter, plant compaction was also optimized for ‘Compacta’ and ‘Super’ within this range. 

Light Manipulation for Ornamental Crop Production

Light Manipulation for Ornamental Crop Production

Figure 2. Production greenhouses growing hanging baskets above rows to maximize their space use efficiency.

One of the most popular hanging basket ferns grown in controlled environments is the Boston fern. Seltsam and Owen (2022) used shade cloths to apply five different levels of DLI to identify an optimal range to grow the species. A DLI range of 10-12 mol m2 d1 Maximized frond number in 7 of 11 cultivars. Based on height and diameter, plant compaction was also optimized for ‘Compacta’ and ‘Super’ within this range.

Shade cloths improve plant structure not only by decreasing PPFD and diffusing light but also by decreasing the amount of heat a crop receives, which impacts stem elongation and leaf expansion (Erwin and Heins, 1995; Dale, 1964, 1965; Milthorpe, 1959). As a result, shade cloths provide ideal conditions for crops that prefer cooler temperatures, such as marigolds, chrysanthemums, and pansies. Austerman et al. (2023) grew pansies for six weeks under red, black, pearl, and aluminized shade cloths to see which color cloth improved plant compaction. 

Pearl-colored shade cloths decreased the height the plant had to reach to flower and grow true leaves, indicating a more compact growth habit, which makes damage during shipment less likely. These examples demonstrate the usefulness of shade cloths to improve plant growth uniformity and compaction by providing more diffuse light and decreasing heat the plants receive.

Decreasing Photoperiod – Blackout Cloths

Another option to decrease DLI is to decrease photoperiod. Growers primarily decrease photoperiod to induce flowering in short-day plants (SDPs), which flower only when the night length is above a critical minimum (Yang, 2022). 

Growers can use blackout cloths to simulate short days. Blackout cloths have synthetic black fibers with reflective outer surfaces that prevent sunlight from reaching the crop. It is common to see them installed as curtains operating autonomously inside greenhouses (Figure   3). 

Ornamental SDPs of economic importance include chrysanthemum, Christmas cactus, and poinsettia. Controlling the flowering of these seasonal specialty crops is necessary to produce marketable plants for sale just before a particular holiday. 

While blackout cloths can induce flowering in SDPs, the next product discussed, supplemental lighting, can be used to delay SDP flowering using night interruption lighting (NIL). NIL involves turning on artificial lights in Figure 3. Blackout clothes are ready to be deployed above chrysanthemums—the middle of the night leads plants to perceive the longest, unbroken darkness period as shorter.

Light Manipulation for Ornamental Crop Production

Figure 3. Blackout cloths are ready to be deployed.

Increasing DLI – Supplemental lighting

Supplemental lighting increases PPFD and extends photoperiod, so the crop receives more photons to drive photosynthesis and increase growth. Traditional supplemental lighting includes metal-halide (MH) lamps, high-pressure sodium (HPS) lamps (Figure 4), and light-emitting diodes (LEDs) (Figure 5). 

LEDs are the newest form of supplemental lighting and have improved features compared to MH and HPS, including higher energy use efficiency, longer working life, and tunable light output (Kim et al., 2004). More and more greenhouses are adopting LEDs due to their energy efficiency and color-tuning properties.

 

Light Manipulation for Ornamental Crop Production

Figure 4. Supplemental HPS lighting in Greenhouse. 

The light quality of  LEDs can be customized, which allows for the application of specific wavelengths to a crop.   In a study by Collado and Hernández (2022), geranium ‘Maverick Red’ and petunia ‘Dreams Midnight ’ were grown in greenhouses under supplemental red LEDs (670 nm) or HPS lamps. Compared to the HPSlight quality, the red LEDs doubled the red light PPFD, increasing the red:far-red light ratio tenfold.   

When the same DLI, the morphology of the geraniums and petunias was more compact under LEDs compared to HPS lamps. Petunia also showed increased chlorophyll and anthocyanin concentrations, contributing to leaf color and ornamental value (Gazula et al., 2007). Figure 5. 

LEDs in controlled environments. (Figure 4). Supplemental HPS lighting over orchids. Additionally, the study included a paclobutrazol (PBZ) application to compare plant compactness resulting from light quality to that from PBZ. 

PBZ is a commonly used ornamental plant growth regulator (PGR) that increases plant compaction but is highly toxic to aquatic life(Syngenta, 2021). The compactness of petunia ‘Dreams Midnight’ was significantly greater under LED treatment than HPS, and the PBZ application did not intensify this effect. These results suggest that light-quality manipulation without PGR compacts petunias. 

Light Manipulation for Ornamental Crop Production

Figure 5. LEDs in controlled environments.

Another benefit of increased red light is that mother plants can produce many cuttings. In Kobori et at. (2022), researchers grew two cultivars of impatiens undersupplemental LED lights supplying 150 μmol m-2s-1 of various red: blue light ratios for 12 hours daily. Two hundred two days after transplant, the treatment receiving the most significant proportion of red:blue light had produced 35% more cuttings than the control, which received no supplemental light. 

The response differed between cultivars, suspected to result partially from higher leaf anthocyanin concentration in ‘Sunpatiens Compact Royal Magenta’ than ‘Sunpatiens Compact White.’ Responding to a question posed by Currey and Lopez (2013), whether the presence of leaf pigments in mother plants affects cutting quality. 

Passive Luminescent Greenhouse Layers

Luminescent layers allow for spectral modification like LEDs, but unlike LEDs, they do not require electricity. They convert portions of solar energy from less to more photosynthetically efficient wavelengths (UV and blue [200-500 nm] to red [600-700 nm]). 

Unlike cloths, the energy is transferred to a different wavelength instead of filtering out, resulting in greater PAR intensities and crop yields. While the documentation of benefits of luminescent layers on edible crop growth exists, benefits to ornamental crops do not; however, fresh-cut flowers that prefer high light intensities, such as gladiolus and chrysanthemum, could benefit. 

Conclusion

Luminescent greenhouse layers use organic dyes and inorganic nanomaterials, including quantum dots. Unlike dyes, quantum dots convert solar energy more efficiently and are more stable under sunlight. Under UbiGro, a quantum dot-based luminescent film (Figure 6), plants receive 10% more red light (600-700 nm) and 4% more far-red (700-750 nm) than sunlight. The ratio of red:far-red and red: blue light increases by 9.5% and 43%, respectively. 

Increasing the proportion of red light prevents shade avoidance syndrome, leading to more desirable ornamental plant growth (Keuskamp, 2010); examples of these effects were more compact geraniums and petunias in Collado and Hernández (2022). Additional characteristics improved by increased red light include a more vibrant leaf color and increased cuttings (Collado and Hernández, 2022; Kobori et al., 2022). 

Additionally, UbiGro provides 5% more green light (500-600 nm) than sunlight. Greenlight has similar effects on plant growth as diffuse light; both penetrate deep into plant canopies, increasing radiation use efficiency and, thus, growth (Tubiello et al., 1997). These light quality adjustments that luminescent films provide are excellent for modifying plant growth. 

Light Manipulation for Ornamental Crop Production

Jeff Bates

Jeff Bates is Plant Biologist at UbiQD, Inc. With professional experience in both crop research and production, he has grown edible, ornamental, and medicinal crops using soilless cultivation methods in various controlled environment settings. These experiences have led him to believe that advancing controlled environment technologies is critical to supporting future generations.

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The Impact of Color on your plants
Hunter McDaniel CEO & Founder UbiGro

Hunter McDaniel, PhD

Founder & CEO

 Hunter earned a Ph.D. in Materials Science and Engineering at the University of Illinois at Urbana-Champaign, before joining Los Alamos National Laboratory in the Chemistry Division. Ultimately the value proposition of UbiGro is about boosting crop yields and quality without the cost or energy impact of lighting. Hunter has more than fifty publications and patents, and more than 2000 total citations, h-index: 20. Hunter fundamentally believes that novel materials underpin every significant technology advancement, and he is focused on leveraging new materials to have a lasting and sustainable impact.

Meet The Team

Damon Hebert, PhD

Director of Agriculture

Damon brings a wide range of experience in agriculture, materials science, spectroscopy, and small business. During his time in Prof. Angus Rockett’s research group at The University of Illinois at Urbana-Champaign (UIUC), Hebert authored a doctoral thesis and multiple papers on the materials science of CIGS semiconductor materials, which is closely related to the materials developed at UbiQD. He also served as a consultant to Nanosolar, a CIGS nanocrystal solar cell manufacturing company. Hebert has industry experience having co-founded Dr. Jolly’s, a leading cultivation and distribution operation in Bend, OR.

Meet The Team

Tania Lafaille

Sales Representative

Tania is a UbiGro Sales Representative, with over 7 years of experience in product sales (specifically berries and avocados) covering all of North America and parts of South America. While in agriculture, Tania has cultivated strong relationships with growers and distributors, granting her a unique insight into both perspectives. That understanding, paired with her fierce dedication to results, drives her fun and fiery commitment to her craft. Tania is based in Gilroy, CA.

Meet The Team

Tyler Veyna

Sales Representative​

Tyler brings 15 years of experience in Greenhouse production and facility management of a wide range of crops in multiple states to the UbiGro team. Based in Salinas, California. “Being a fourth-generation farmer, I look to improve and empower the grower, and with UbiGro, we can do just that.”

Meet The Team

Jim Gideon

Sales Manager

Jim Gideon is an UbiGro Sales Manager, with over 25 years of greenhouse industry sales experience covering all of North America. Previously Jim has worked for Green Tek, Plazit-Polygal, Texel, Cherry Creek, and Nexus. He is based in Montgomery, AL, and Jim believes that “light is everything to the grower.”

Meet The Team

Eric Moody

Director of Sales

Eric Moody is UbiQD’s Director of UbiGro Sales. Eric has more than 6 years of experience in horticulture lighting industry, building relationships with greenhouse growers of all sizes and crops on optimal lighting for their growing operation, and most recently managed a North American sales team for PL Light Systems. Overall, Eric has been in sales leadership positions for more than 13 years. Eric brings with him a great understanding of the market and available technologies for growers, greenhouse facilities, and sales leadership. Reach Eric by phone at 541-490-6421 or by email at [email protected].

Meet The Team

Mike Burrows, PhD

VP of Business Development

Dr. Michael Burrows is UbiQd’s Vice President of Business Development. His educational background includes a Materials Science doctorate from the University of Delaware and an MBA from Duke University Fuqua School of Business. His career has specialized in the commercialization of novel electronic materials in venture-run programs for different industries including solar, biosensors, and the automotive industry. In both start-up and corporate environments, he has extensive experience in global market development, foraging supply chain partnerships, productization, and brand building. He is currently leading UbiQD’s partnership efforts in luminescent greenhouse technology, smart windows, and security ventures.

Meet The Team

Matt Bergern, PhD

Cheif Product Officer

As Chief Product Officer at UbiQD, Dr. Matt Bergren leads the company’s product development efforts, sales, and product manufacturing, including the company’s first commercial agriculture product, UbiGro. He plays a critical role in continuing the company’s path of technology development and vision of powering product innovations in agriculture, clean energy, and security.

He serves as the principal investigator for UbiQD’s contract with NASA, focused on tailoring the solar spectrum for enhanced crop production for space missions. Dr. Bergren’s leadership experience includes serving on the board of directors for the New Mexico Energy Manufacturing Institute, focused on job creation in New Mexico’s energy, and related manufacturing community.