Growing the Best Phalaenopsis - Michigan State University

CULTURE CORNERGrowing the Best PhalaenopsisPart 2: Media, Transplanting, Water and Nutrient RequirementsText by Yin-Tung Wang, PhD, Matthew Blanchard, Roberto Lopez and Erik Runkle, PhD/Photographs by Yin-Tung Wang, PhDMANAGING THE ROOT ZONE OFpotted orchids can be one of the mostcritical aspects to growing a healthycrop. If one can grow plants withhealthy roots, making them flower is amuch easier task. In this second articleof our four-part series, we presentresearch-based information on howmedium, watering and fertility influencegrowth of potted phalaenopsis.MEDIA COMPONENTS In theirnatural habitats, most phalaenopsisspecies are epiphytic plants, meaningthat they grow on tree trunks and limbs.Their roots are exposed to air movementand absorb moisture from the humid air,as well as from rains and dews. Becauseof this, when we grow phalaenopsis incontainers filled with an artificialmedium for our convenience, we mustconsider aeration, capillary action,water and nutrient-holding capacities,stability and weight of the mediumcomponents, as well as cost andconsistency.Coarse materials are often used toallow for plenty of air movementthrough the medium. Ground bark fromDouglas fir and coastal redwood treeshas been used for more than half acentury for growing orchids. AlthoughDouglas fir and coastal redwoodare host plants for Phytophthoraramorum, the fungus that causessudden oak death disease in Californiaand Oregon, orchids grown in barkhave been exempt by USDA from thequarantine list.Nearly all commercial orchidgrowers make their own media.Although most modern orchid mediastill contain fir bark, one or more of thewater-absorptive materials such assphagnum peat, perlite, sphagnummoss, coconut husk chips and diatomiteis mixed with bark for improvedplant growth. For example, earlyresearch at Texas A&M Universityshowed that plant growth was vastlyimproved in a medium consisting of 20percent coarse sphagnum peat and 80percent fir bark, compared with fir barkalone.Bark Fresh ground bark does nothold much water, which can be prob-106 ORCHIDS FEBRUARY 2007 WWW.AOS.ORG

CULTURE CORNER242 ppm (with 100 or 200 ppm ofnitrogen) did not influence growth orflowering of phalaenopsis. Preliminaryresearch indicates that 25 to 50 ppmphosphorus is adequate to grow anexcellent crop. Research has shownthat when potting newly imported barerootphalaenopsis for inducing spikingsoon, phosphorus did not affectspiking or flower count during the firstflowering season.For growers in cool conditions,consider using a lower fertilizer rateduring the flowering cycle due toreduced vegetative growth. Fertilizationcan be withheld completelyonce an inflorescence has reached 10inches (25 cm) in length, or after thefirst flower has opened, withoutaffecting flower count or size.A recently completed study showedthat phalaenopsis that did not receiveadequate levels of potassium mayappear healthy for several months,producing a similar number and size ofnew leaves as those receiving adequatepotassium. As soon as spiking hastaken place and while the younginflorescences grow, the limited poolof potassium in the leaves and roots isremobilized to support the reproductivegrowth and the lower leaves start toshow symptoms of potassium deficiency.Although plants that weredeficient of potassium producedflowers, a few lower leaves were lost.All phalaenopsis planted in a barkmix and lacking potassium eventuallydied.Continuous application of nitrogenensures flower longevity, but does notincrease flower count after the spikeshave reached 10 inches (25 cm) inlength. Results from a recentlycompleted study at Texas A&MUniversity suggest that fertilizers highin ammoniacal nitrogen are not desirablefor the best vegetative growthand flowering. There has been plenty ofevidence to suggest that phalaenopsisplants must already have had adequatephosphorus and potassium in theirtissues prior to spiking for best performance.Potassium at 200 to 300 ppmensures high flower count and maximizesflower size.SALINITY Roots of phalaenopsisare sensitive to salinity and can beinjured when salts accumulate in themedium. In one study, when salinity ofthe irrigation water (before adding anyfertilizer) increased from 0 to 1.4 dS/m,root fresh weight decreased. Many110 ORCHIDS FEBRUARY 2007 WWW.AOS.ORG

orchid growers have installed reverseosmosis (RO) equipment to providewater that is low in dissolved salts. Ifstraight RO water is used for irrigationfor extended periods, supplementalcalcium and magnesium must be usedto avoid deficiency problems. Adesirable electrical conductivity (EC)of the water before adding fertilizer is0.5 dS/m or less. We recommend thatgrowers maintain a medium leachate of1.0 to 1.5 dS/m or lower when using thepour-through technique. When mediumEC becomes too high (2.0 dS/m), timelyleaching with clear water is recommended.Techniques for determining thesalt level in the root medium are in theSeptember 2006 issue of Orchidsmagazine (page 633).The third part of this series in theMarch 2007 Orchids will focus on lightand temperature requirements forvegetative growth and flowering,height control and managing diseasesand insects.AcknowledgmentsThe authors thank the Fred C. GloecknerFoundation, the American Orchid Society,Taiwan Sugar Corporation, Matsui Nursery,Project GREEEN, various local orchidsocieties, and private greenhouse companiesand individuals that support orchid research.Yin-Tung Wang, PhD, is professor offloriculture at Texas A&M University(e-mail yt-wang@tamu.edu). MatthewBlanchard and Roberto “RoLo” Lopezare graduate assistants and ErikRunkle, PhD, is assistant professorand floriculture extension specialistat Michigan State University (e-mailrunkleer@msu.edu).OPPOSITE The effect of potassiumconcentration in fertilizer solution onphalaenopsis growth and flowering. Theplants received 0, 50, 100, 200, 300, 400,or 500 ppm potassium in the nutrientsolution (left to right) since July 1, 2005.These photographs were taken at theTexas A&M University System AgResearch Center, Weslacoon, Texas, onDecember 12, 2005 (top); February 24,2006 (middle) and June 28, 2006 (bottom).ABOVE Many plants of PhalaenopsisGalypso (Brother Delight × violacea) bearfragrant flowers, a trait inherited from thePhal. violacea parent.(This article is part of a series originallypublished in Greenhouse Grower magazine.It has been modified for orchid enthusiastswith a wide range of growing experiences.)WWW.AOS.ORG FEBRUARY 2007 ORCHIDS 111