E-GRO Alert

e-GRO AlertVolume 2, Number 20 April 2013Managing Temperature and Light to Reduce Shrinkand Increase QualityRoberto Lopez, Purdue Universityrglopez@purdue.eduOver the last few weeks I havevisited over 15 greenhouseoperations ranging in sizefrom four Quonset structuresto over 30 acres. What Ihave found in almost allfacilities is crop delay andlower quality plants dueto improper temperatureand light management.However, I have also foundnumerous operations thatare properly managing theirgreenhouse environment Figure 1. Compartmentalization of cold-senesitive greenhouse cropswith great results quality crops such as vinca can reduce energy costs.ready at the proper time. plant development? The grow and eventually flowersdevelopmental rates of when outdoor temperaturesCropplants (such as the rate to natural increase? This speciesCompartmentalization unfold a leaf or time to flower) dependent temperature atW h a t d o a n g e l o n i a , decreases as temperature which plant developmentc e l o s i a , l a n t a n a , N e w d e c r e a s e s . A s p l a n t stops is referred to as the baseGuinea Impatiens, pentas, temperature decreases, temperature. The estimatedportulaca, and vinca all have plants develop progressively base temperature for mostin common? They are all slower and, at some point, floriculture crops rangesheat loving annuals that are they stop developing. Have from 32 to 50 F and speciesconsidered cold-sensitive. you ever seen a stalled can be classified as coldWhy are they categorized vinca crop on a greenhouse tolerant, cold-intermediate,as cold-sensitive in terms of bench that finally begins to and cold-sensitive. So whatNC STATE UNIVERSITYFloriculture

Volume 2, Number 20e-GRO Alert - 2013e-GRO AlertVolume 2, Number 20April 2013www.e-gro.orgCONTRIBUTORSDr. Nora CatlinFloriculture SpecialistCornell Cooperative Extension Suffolk Countynora.catlin@cornell.eduDan GilreinEntomology SpecialistCornell Cooperative Extension Suffolk Countydog1@cornell.educan greenhouse growersdo to accommodate coldsensitive species that have abase temperature above 46 F? By having a separate bay,this greenhouse provides allits cold-sensitive annualssuch as vinca with optimaltemperatures for plantdevelopment saving itself a lotof money on energy (Figure 1).Delayed Crops due toDrafty or Open DoorsHave you ever noticed thatplants near side walls or doorscan be delayed? In myrecent visits, I have seen asignificant delay across coldtolerant, -intermediate and-sensitive crops. For example,the constant opening andclosing of the sliding doorDr. Brian KrugFloriculture Ext. SpecialistUniv. New Hampshirebrian.krug@unh.eduDr. Joyce LatimerFloriculture Extension & ResearchVirginia Tech Universityjlatime@vt.eduDr. Roberto LopezFloriculture Extension Specialist &ResearchPurdue Universityrglopez@purdue.eduDr. Paul ThomasFloriculture Extension & ResearchUniversity of Georgiapathomas@uga.eduDr. Brian WhipkerFloriculture Extension & ResearchNC State Universitybrian whipker@ncsu.eduFigure 2. Delayed andunmarketable coleus crop nearthe sliding door in a Quonsetgreenhouse.Copyright 2013Permission is hereby given to reprint articlesappearing in this Bulletin provided thefollowing reference statement appears withthe reprinted article: Reprinted from thee-GRO Alert.Figure 3. A polycarbonatebarrier has been used in thisgreenhouse to prevent coldair from lowering the planttemperature of crops near thedoor.2013SponsorWhere trade names, proprietary products, orspecific equipment are listed, no discriminationis intended and no endorsement, guarantee orwarranty is implied by the authors, universitiesor associations.In cooperation with our local and state greenhouse organizations2

Volume 2, Number 20e-GRO Alert - 2013in this Quonset resulted inthe delay and potential lossof nearly 20 flats of coleus(Figure 2). Can anythingbe done to prevent coldair from reaching the cropbelow? This greenhousefacility has constructedan inexpensive wall madeout of old polycarbonatematerial to prevent the colddraft from lowering planttemperature and delaying Figure 4. Heat stress symptoms of ivy geranium near a forced airthe crop (Figure 3).Temperature sensitivityof Ivy GeraniumHow close is “too close” whenplacing hanging basketsnear forced air heaters? Inthis example, we can seethe effects of heat stress(whitening and chlorosis ofyoung, developing leaves)on ivy geranium baskets asthey were placed too closeto forced air heaters (Figure4). In addition to heat stress,other species such as petuniaFigure 5. A dense fern hanging basket crop placed above a lowcan dry out, desiccate and light requiring crop.ultimately lead to cropshrinkage.Excessive Shading fromHanging Basket CropsTime and time again I findgrowers placing an excessivenumber of hanging basketsabove their other crops,leading to the use ofadditional plant growthregulators (PGRs) to minimizestretching or poor-qualityFigure 6. A dense flowering hanging basket crop placed abovecrops. In this example, the a medium to high light requiring crop.3

Volume 2, Number 20e-GRO Alert - 2013grower has placed a verydense fern hanging basketcrop over a low lightrequiring begonia crops(Figure 5).Although I do notrecommend this strategy,it is much better thanplacing a dense hangingbasket crop abovemedium- or high-lightcrops, as we can see inthis example (Figure 6).Research has shown thatbasket color can influencethe light transmission to thecrop below, with whiteand green baskets (noplants) providing 13 and25% shading, respectively.Additionally, undera typical greenhousehanging basket scenario,shading can be in excessof 45% as plants grow overthe sides of the basket.Green - Purple FountainGrassPurplefountaingrass(Pennisetum setaceum‘Rubrum’) is a popularannual ornamental grass thatappeals to consumers due toits dark purple, arching foliageand light purple flower spikes.The purple pigmentation ishighly dependent on lightand can range in colorfrom pale green in low-lightgreenhouse environmentswith excessive shading fromFigure 7. Purple found grass grown under low light conditions(ie. under a hanging basket crop) will remain green.Figure 8. Purple fountain grass grown under moderate lightconditions will have light-purple foliage.hanging baskets (Figure 7)to dark purple in high-lightgreenhouse environments orunder supplemental lighting.A study at Michigan StateUniversity found thatplants grown outdoorsproduced dark purplefoliage and flower spikes,and the purple colorationcovered the entire leaffrom the base to the leaf tip4throughout the canopy.When plants were grownunder the typical northerngreenhouse environment,plants had light-purplefoliage from mid-leaf to tipand were most purple at thetop of the canopy (Figure8). Leaves in the bottomand middle of canopyhad low anthocyanincontent and appearedmostly green in color.

Volume 2, Number 20e-GRO Alert - 2013Take Home MessageBoth cold and heat stress ofgreenhouse crops can occurat any time during the springbedding plant season due toimproper plant placement.Stretch and poor qualitycrops such green foliagepurple fountain grass areprimarily influenced by lowlight environments. However,greenhouse operators canincrease the amount oflight their plants receive byreducing excessive shadingfrom hanging baskets, shadecurtains or whitewash or byproviding supplemental lightfrom high intensity discharge(HID) lamps. By properlymonitoring and managingthe greenhouse environment,growers can increase thequality of their crops andreduce losses due to shrink.5

In cooperation with our local and state greenhouse organizations 2013 Sponsor Figure 2. Delayed and unmarketable coleus crop near the sliding door in a Quonset greenhouse. Figure 3. A polycarbonate barrier has been used in this greenhouse to prevent cold air from lowering the plant temperature of crops near the door. can greenhouse growers