Lighting Research

Flowering of many popular ornamentalcrops is determined by day length. Whenthe natural days are short, low-intensitylighting during the middle of the night(night interruption, NI) or at the end of theday promotes flowering of long-day plantsand inhibits flowering of short-day plants.For long-day plants, a 4-hour NI ismended for the most rapid and uniformflowering.

Conventional broad-spectrum lightsources, such as incandescent (INC) andhigh-pressure sodium (HPS) lamps, areeffective at creating long days. However,INC lamps are very energy inefficient andare being phased out ofproduction. HPSlamps are more energy efficient, but in mostcommercial installations, they deliver ahigher intensity than needed to regulateflowering and consume a large amount ofe1ectricity Light-emitting diodes (LEDs)potentially consume less energy, enabledelivery of specific colors of light, and inmany cases, have a very long operating life.For the past three years, one of the majorresearch thrusts at Michigan StateUniversity (MSU) has been to better under-stand how different colors of light, deliveredby LEDs, regulate flowering.

As part of this project, we have beenexperimenting with LEDs recently developed by Philips Lighting. Philips currentlyproduces three types of screw-in LED lampswith potential flowering applications andinclude deep red (DR), white (W) and/orfar-red (FR) LEDs:

. FR only

. DR+W

. DR+W +FR

The 14-watt DR+W+FR LED lamp wasdeveloped as a commercial replacement for1 00 or 1 50-watt incandescent lamps usedfor photoperiodic lighting. The DR÷Wlamp was developed for crops that don’t

need FR light for flowering, which includesmost short-day plants. Without the FRlight, plants are typically shorter. However,because flowering of some crops is regulatedby R and FR light, the DR+W+FR lampwas developed for use on all day length-sensitive crops.

From January to June 20 1 3, we coordinated commercial greenhouse grower trialsto investigate the efficacy of the PhilipsDR+W+FR LEDs at controlling floweringof day length-sensitive bedding plants. Theparticipating companies were C. Raker &Sons (Litchfield, Michigan), the Center forApplied Horticultural Research (CfAHR) atAltman Plants (Vista, California), HenryMast Greenhouse (Byron Center,Michigan) , Krueger-Maddux Greenhouses(Sunman, Indiana) and Kube Pak(Allentown, New Jersey) . The trials were alsoperformed in two separate greenhouses atMSU. Based on previous research performedat MSU, we postulated that the DR+W+FRlamps were at least as effective as conventional lamps for regulating flowering.

Grower trial protocolSeeds of ageratum Hawaii Blue, dianthusTelstar Crimson, petunia Easy WaveBurgundy Star and Wave Purple Classic,snapdragon Liberty Classic Yellow and verbena Obsession were sown in 288-cell plugtrays and cuttings of calibrachoa Callie anddahlia Dahlinova Texas were propagated in51-cell strip trays by C. Raker & Sons.These plants were sown at the same timeand shipped to all participating growers inlate January. The typical young plant pro-duction durations were shortened by oneweek in an attempt to ship vegetative (non-induced) plants.

Upon receipt, each grower transplantedthe plants into 1801 trays using their typical growing media for bedding plant pro-duction and placed four trays of each cropunder each treatment. All plants weregrown under similar environmental conditions following the growers’ standard pro-duction practices of watering, fertilizationand pest management. The average dailytemperature ranged from 62F (16C) at

Krueger-Maddux Greenhouses to 71F (21C) at CfAHR.The average daily light integral (DLI) ranged from 9molm2d1at Henry Mast Greenhouse to 20 molm2d1at CfAI-{R. Applications of plant growth retardants were atthe discretion of the growers, and if an application wasmade, it was the same in all treatments.

The plants were grown under natural short days at alllocations except for MSU, where 9-hour short days wereprovided. Two different 4-hour NI lighting treatments weredelivered by the DR+W+FR LEDs or conventional lampsthat the growers had used previously. INC lamps were usedat Krueger-Maddux Greenhouses, Kube Pak, CfAHR andMSU, while HPS lamps were used at C. Raker & Sons andHenry Mast Greenhouse. CfAHR delivered a natural shortday (Figure 1), MSU delivered a 9-hour short day and KubePaic delivered a 4-hour NI by compact fluorescent (CFL)lamps. Depending on location, the lamps were installed 3 to7 ft. above the plant canopy and 3 to 10 ft. apart. All lampsoperated from 10:00 p.m. to 2:00 a.m. every night. If twotreatments were close together, a light barrier was pulled atnight to block all direct light from adjacent treatments.

Date of transplant and date of the first open flower wererecorded for 1 2 random plants of each crop under eachtreatment. Plants were checked every day or two for firstflowering at most locations, or once or twice a week atKube Pak. Flowering percentage and days to flower werecalculated for each treatment and additional flowering datawere recorded for the treatments at MSU.

Grower trial resultsC. Raker & Sons—All plants flowered under either theHPS lamps or LEDs. There was no significant impact oflamp type on flowering time for any crop except for verbe

na, which flowered approximately eight days earlier underthe HPS lamps than under the LEDs. This could be at least

: partially attributed to a higher average daily temperature (by4 degrees F) and DLI (by 4 mo1m2.d1)under the HPSlamp treatment.

CEAHR—A11 crops under the INC lamps and LEDsflowered at approximately the same time, whereas some of

the long-day plants did not flower under the natural shortdays. For ageratum, dahlia, dianthus, petunia Easy WaveBurgundy Star and verbena, there were no differences inflowering time among all treatments, probably because thenatural photoperiod and/or DLI in Vista, California, weresufficient for flower induction. Calibrachoa and snapdragonflowered earlier under the NI lighting treatments than

undershort days (Figure 2).

Henry Mast Greenhouse—All plants flowered similarly

under the HPS lamps and LEDs, except only 8% of snap-dragon under the HPS lamps had flowered when the trialended.

Krueger-Maddax Greenhouses—All plants floweredsimilarly under the INC lamps and LEDs except for >>>

BY QINGWU MENG & ERIK S. RUNKLE

Control Flowering with LEDsIs it worth paying extra for LEDs? Researchers at Michigan State University foundthat the long-term benefits may outweigh the up-front costs.

Figure 1. Setup of treatments, including a natural short day and a 4-hour night interruption from incandescent or thePhilips deep red ÷ white + far red (DR÷W÷FR) LEDs, at the Center for Applied Horticulture Research at Altman Plants.

Figure 2. Calibrachoa and snapdragon grown under natural short days without or with a 4-hour nightinterruption from incandescent or the Philips deep red + white + far red (DR+W+FR) LEDs at the Center forApplied Horticulture Research at Altman Plants. Average days to flower followed by different letters (inwhite font) are significantly different. Flowering percentage is in yellow font.

Figure 3. Ageratum, dianthus and petunia grown under 9-hour short days without or with a 4-hour nightinterruption from incandescent or the Philips deep red + white + far red (DR+W÷FR) LEDs at MichiganState University. Average days to flower followed by different letters (in white font) are significantlydifferent. Flowering percentage is in yellow font.

62 GROWERTALKS I MARCH14

Lighting Research

snapdragon, which flowered approximatelyeight days earlier under the INC lampsthan under the LEDs.

Kube Pak—Petunia Wave Purple Classicdid not flower under the CFL lamps beforethe trial ended. We have previously shownthat CFLs are not very effective at inducingflowering of petunias, as well as a few otherlong-day plants. For ageratum, dahlia,dianthus and snapdragon, flowering timewas similar among all treatments. PetuniaEasy Wave Burgundy Star and verbenaflowered earlier under the LEDs than underthe INC lamps. Calibrachoa flowered earlier under the LEDs than under the CFL andINC lamps.

MSU—Ageratum, dianthus, petuniaEasy Wave Burgundy Star and Wave PurpleClassic, and snapdragon flowered similarlyunder the INC lamps and LEDs and earlierthan under short days (Figure 3). The flowering responses of calibrachoa and dahliawere inconsistent in the two greenhouses.Verbena flowered earlier under the INClamps and LEDs than under short days; but

in one greenhouse, flowering was the mostrapid under the INC lamps. Except fordahlia and petunia Wave Purple Classic,plant height at flowering was similar underthe INC lamps and LEDs. For example, thestem with the first flower of petunia WavePurple Classic was approximately 2 in.longer under the LEDs than under the INClamps.

ConclusionsWith a few exceptions, flowering of thebedding plant crops tested was similarunder the Philips DR+W+FR LEDs asunder the conventional lamps. Therefore,we conclude that in most instances, theDR+W÷FR LEDs are as effective as lampstraditionally used in greenhouses. Given thecomparable effectiveness of the LEDs andconventional light sources, factors such asenergy consumption, lamp longevity andinvestment payoff should be considered.

The DR+W+FR LEDs are more efficient than most types of conventional

lamps, since they only consume 14 wattsper lamp. The useful lifetime of these LEDsat 77F (25C) and 90% intensity is at least20,000 hours, while that of incandescentbulbs is usually around 1,000 hours. Thegreater energy efficiency and much longerlifetime should be weighed against thehigher purchase price of the LEDs versusincandescents. Given our research findings,the efficacy of the LEDs should not be afactor. GT

Qingwu (William) Meng is an MS. studentand Erik Runkie (runkleer@msu.edu) is anassociate professor and floriculture extensionspecialist in the Department of Horticulture atMichigan State University. The authors thankC. Raker & Sons, the Center for AppliedHorticultural Research at Altman Plants,Henry Mast Greenhouse, Krueger-MadduxGreenhouses and Kube Pak for their cooperation with this project. They also thank PhilipsLighting and HortAmericas for subsidizing thecost of the LEDs and funding provided by theUSDA National Institute of Food andAgriculture’s Specialty Crop Research Initiativeand MSU’s Project GREEEN.

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