Growing Seedlings Under LEDs: Part Two

Light-emitting diodes (LEDs) present opportunities for horticultural lighting because of their high electrical efficiencies and tunable light spectrums. Today, LED arrays are similarly or more efficient than conventional lamps such as high-pressure sodium (HPS) or fluorescent, and their efficiencies continue to increase. The wavelengths, or colors, of commercially available LEDs vary widely, which allows unique mixtures of colors to be developed that can result in desirable growth responses. For example, manipulating light quality to produce short, well-branched plants could reduce the need for plant growth retardants or other height-suppressing strategies.

In Part I of this article (January GG), we presented results from our indoor LED lighting experiment with orange, red and hyper red light. We concluded that because plants grew similarly under different colors of red light, red LEDs for horticultural applications could be chosen based on their longevity, efficiency and cost, without affecting plant quality.

In our second experiment, tomato ‘Early Girl,’ salvia ‘Vista Red,’ petunia ‘Wave Pink’ and impatiens ‘SuperElfin XP Red’ were grown in growth chambers, beginning after germination, for four weeks at 68°F. The photosynthetic light intensity was fixed at 160 µmol∙m-2∙s-1 and was delivered for 18 hours each day. Light was delivered using different percentages of blue (B; peak of 446 nm), green (G; peak of 516 nm) and red (R) light. The red light was delivered by equal intensities of two different LEDs with peak wavelengths of 634 or 664 nm. The LED treatment percentages were: B25+G25+R50 (25 percent of light from blue and green LEDs and 50 percent from red LEDs), B50+G50, B50+R50, G50+R50, R100 and B100. Plants were also grown under cool-white fluorescent lamps to serve as a control treatment. A variety of data were collected, including the fresh weight of the shoots, seedling height and total leaf area.

Plants Grown Under Different Color Light Finished At Various Heights

Plants were 40 to 60 percent shorter when grown under at least 25 percent blue light as compared to plants grown under only red light (Figures 1 and 2). Plants grown under 50 percent green light were shorter than those under all red, but taller than those grown with some blue light. The leaf area of plants grown under only red light was 50 to 130 percent greater than with 25 percent or more blue light. Similarly, plants had 50 to 110 percent greater shoot fresh weight under only red light than plants under 25 percent or more blue light (Figure 3). Plants grown under fluorescent lamps often had fresh weight and leaf area similar to that of the plants grown under only red light, while their height was similar to plants under the G50+R50 treatment. Impatiens was the only species to produce flower buds during the experiment, but only under at least 25 percent blue light. The number of leaflets of tomato that developed edema was greatest under only red light, and edema decreased as the percentage of blue light increased.

In a third experiment, the same species of bedding plants were grown for four weeks, also at 160 µmol∙m-2s-1, under different percentages of blue and red light. The LED treatments were all red (R100), all blue (B100) or the following percentages: B6+R94, B13+R87, B25+R75 and B50+R50. The red light was delivered by two different red LEDs as in the previous experiment. Plants grown under at least 6 percent blue light were 25 to 50 percent shorter than plants without any blue light (Figure 4). Leaves of impatiens, salvia and petunia were approximately twice as large when grown under only red light compared to leaves on plants under at least 50 percent blue light. Similar to the second experiment, providing an increasing percentage of blue light resulted in more flower buds on impatiens and less edema on tomato.

LEDs Can Help Growers Produce Young Plants With Desired Growth Attributes

We can conclude that adding blue light to the spectrum inhibits stem elongation and leaf expansion, while growing plants under only red light can increase stem length and leaf size. Twenty-five percent green light can substitute for 25 percent blue light without affecting fresh weight, but plants will be taller. However, the electrical efficiency of green LEDs on the market today is much lower than that for blue LEDs, so the economics of using green LEDs in young plant production are probably unfavorable. Adding blue light to a red-dominant environment stimulated flowering in impatiens and decreased the incidence of edema in tomato.

The ratio of blue and red light can be adjusted to produce seedlings with desired leaf sizes and stem lengths. Red light increased leaf size and stem length, which resulted in plants that had the greatest biomass. Plants under at least some blue light were more compact and generally were of greater horticultural quality, but leaf size was also reduced, which subsequently suppressed shoot growth.

This information can be used to help growers produce young plants with desired growth attributes, which can’t easily be done with conventional lighting technologies Light spectra could even be fine-tuned during crop production; for example, the proportion of blue light could be increased if seedlings are getting too tall.

Editor’s Note: The authors thank Mike Olrich for his technical assistance, funding from Osram Opto Semiconductors, the USDA Floriculture and Research Initiative and private companies that support MSU Floriculture.

Topics: ,

Leave a Reply

More From Plant Culture...

April 17, 2015

Sakata Seed Uses California Spring Trials Display Plants To Give Back

Sakata Seed America is putting its post-CAST (California Spring Trials) plants and flowers to good use to support events in local California communities of Salinas and Morgan Hill. The plants, along with donations through Sakata's Charitable Giving Program, will support three fun-filled community events that promote healthy lifestyles and support the agricultural industry.

Read More
Hakonochloa macra Aureola v

April 17, 2015

Ornamental Grasses — A Few Thoughts

Grasses have been embraced by growers, landscape architects and retailers, and are an important component in wholesale and resale sales. Allan Armitage shares some popular grasses, one to avoid and a few to use with caution.

Read More
PW_CAST15

April 17, 2015

Allan Armitage’s Favorite Plants From Proven Winners, Syngenta And Danziger

Between visiting California Spring Trial giants like Proven Winners, Syngenta and Danziger, Allan Armitage saw a lot of great plants in one day. Despite the size of the challenge, Dr. Armitage finds a few favorites he thinks you should try.

Read More
Latest Stories
Bee on a Sedum

March 17, 2015

4 Key Pollinator Research Projects To Be Funded By Hort…

The Horticultural Research Institute will grant $125,000 in financial support for four key projects as part of the Horticultural Industry Bee & Pollinator Stewardship Initiative. The Initiative has three primary goals. First, to convene a task force to develop a bee and pollinator stewardship program, including creation of best management practices for plant production. Second, to identify and fund research that will help answer key science questions and fill gaps needed to design and refine the stewardship program. Third, to seek to positively position the horticultural community and its customers by collaborating with other compatible groups interested in augmenting pollinator habitat and protection.

Read More

March 11, 2015

Pollinator Initiative Promotes Bee-Friendly Talking Poi…

AmericanHort and the Society of American Florists are working tirelessly with the ornamental industry's Pollinator Stewardship Initiative on a number of new projects.

Read More

February 11, 2015

Infusion Technology Boosts Seed Performance, Study Sugg…

Seven-year-old wheat seed germination can increase by as much as 83 percent, according to a Vital Force Technology Study that looks at the effects of energy infusion technology on plant vitality.

Read More

February 3, 2015

American Floral Endowment Accepting Research Pre-Propos…

If you are pursuing a floriculture research project, now is the time to apply for funding through the American Floral Endowment. Research pre-proposal applications for 2015-2016 funding are due to AFE by June 1, 2015.

Read More

January 27, 2015

Marijuana’s Trajectory And Ascent To Horticultural Cr…

Marijuana growing is poised for change as growers and researchers focus on improving production practices.

Read More

December 9, 2014

Greenhouse Production: Two Years Of Basics & Beyond…

Greenhouse Grower's Basics & Beyond articles cover some of the latest news and research going on in greenhouse production. Here are article links for the last two years.

Read More
GrowIt! App Wins Gold At Design100 2014 US Mobile & App Design Awards

November 24, 2014

GrowIt! App Wins Gold At Design100 2014 US Mobile &…

The social garden app GrowIt! takes the Gold Winner award at the design100 2014 Mobile & App Design Awards.

Read More

November 10, 2014

The Perennial Farm Joins HGTV HOME Plant Collection

The Perennial Farm joins the HGTV HOME Plant Collection growers' network for 2015.

Read More
AmericanHort

November 4, 2014

AmericanHort Publishes Revised American Standard For Nu…

AmericanHort announces the revised American Standard for Nursery Stock (ANSI Z60.1) is now available for industry use. The Standard reflects the consensus of the industry regarding how nursery stock — living plants other than annuals — should be specified and sold within the trade.

Read More

September 26, 2014

Master The Art Of Watering

Watering is elemental to healthy plants, but one of the hardest concepts for new employees to master in the greenhouse. Recommend these tips to start them off right.

Read More

September 16, 2014

Ball FloraPlant’s Las Limas Facility Provides Gro…

Ball FloraPlant’s Las Limas farm in Esteli, Nicaragua, is one year away from full production, but sales and quality from the two-year-old facility are right on track.

Read More
Erysimum 'Cheers' from Darwin Perennials

September 15, 2014

Darwin Perennials Takes Production Offshore In Bogota, …

With its recent purchase of a farm in Colombia, Darwin Perennials is ready to amp up supply of its perennial genetics, to provide growers with tried-and-true varieties and comprehensive production specifications.

Read More

July 23, 2014

Plan Now To Prevent Bract Edge Burn On Poinsettias

Reduce fertilizer and water, and allow your poinsettias to develop slowly during the final four weeks of production to avoid bract edge burn.

Read More

July 11, 2014

Growing Your Crops Above Their Base Temperature

Lowering temperature set points in the greenhouse may help you combat rising heating costs.

Read More

May 1, 2014

Growers Report Nutritional Problems On Geraniums

In recent weeks, several growers have contacted Michigan State University Specialists about leaf discoloration on geraniums, especially the purpling of lower leaves.

Read More

April 22, 2014

How Two Postharvest Care Products Worked On Potted Plan…

What your potted plants look like at retail translates to sales or fails. North Carolina State University researchers report on how two postharvest care products performed.

Read More
Dianthus 'Passion' from Emerald Coast Growers

March 27, 2014

Growing Dianthus Successfully

Here's some advice on transplanting and producing this classic perennial favorite.

Read More
Aquilegia canadensis

March 10, 2014

Tips For Producing Aquilegia

Advice on planting, temperature, vernalization, lighting and more on columbine from Emerald Coast Growers' head grower Josiah Raymer.

Read More