Poinsettia height control involves careful application of height regulation without compromising plant quality. The use of PGRs is a standard practice in poinsettia height regulation. However, excessive application of PGRs can result in permanent growth suppression and subsequent stunting of poinsettias as well as reduced bract size (Faust et al., 2001; Lewis et al., 2004; Niu et al., 2002), whereas application of too little PGR may not sufficiently suppress stem elongation. Manipulating the difference between day- and nighttime temperatures (referred to as DIF) also can be an effective method of height control (Berghage and Heins, 1991; Moe et al., 1992). However, DIF is difficult to implement in warm, humid climates such as in the southeastern United States, because of the difficulty of cooling greenhouses in late summer, when shoot elongation of poinsettia is rapid. In addition, when multiple crops are grown in one greenhouse, DIF cannot be used to control growth of individual crops, because all crops are exposed to the same environmental conditions.
The use of WD has been studied as an alternative means of height regulation and requires careful management to achieve desired results. Improperly regulated or excessive WD can result in poor-quality plants (Liptay et al., 1998). Barrett and Nell (1982) showed that increasing the irrigation interval reduced the height of poinsettia, but also decreased bract, leaf, and total shoot dry weight. Just like PGR application, timing of WD application is important for height regulation (Niu et al., 2002). Preferably, height regulation through WD should be used during vigorous vegetative growth, when the stem elongates most rapidly. We have previously shown that a controlled WD, reducing θ to 0.20 m3·m−3 as needed, can be an effective method of regulating elongation of poinsettia (Alem, 2014).
The target height of greenhouse crops, including poinsettia, is often determined by market demands or grower preferences (Clifford et al., 2004; Currey and Lopez, 2011; Fisher and Heins, 1995). The desired target height influences how much growth suppression is required during the poinsettia production cycle. Although there is a lot of information about the effects of PGR application rate, concentration, and frequency (e.g., Hammond et al., 2007; Latimer et al., 1999), there is little information about WD as a means of plant height regulation. Drought severity and frequency are known to result in different levels of growth suppression in many species such as salvia (Salvia splendens), Big bend bluebonnet (Lupinus havardii), petunia (Petunia ×hybrida) (Burnett et al., 2005; Niu et al., 2007; van Iersel et al., 2010), and petunia (Barrett and Nell, 1982). Alem (2014) recently reported that controlled WD can effectively regulate poinsettia height without compromising plant quality. In that study, a total of 15 d of WD reduced plant height by 10% (5 cm) compared with that of control plants.
However, application of WD as a means of poinsettia height regulation has not been popular in the past as a result of the risk of excessive stress and plant loss. The use of soil moisture sensor-based precision irrigation systems (Nemali and van Iersel, 2006) can give growers much better control of the severity and duration of the WD, eliminating the risk of excessive drought stress. Such irrigation systems have been tested in greenhouses and nurseries (Chappell et al., 2013) and provide growers with the needed tools to control WD.
We hypothesize that a range of poinsettia heights can be achieved by applying different durations of WD. To test the use of WD as a means of height regulation, the objectives of this study were to determine 1) whether different plant heights can be achieved by application of WD; and 2) how this affects plant quality.
AlemP.2014Irrigation fertilization and non-chemical plant growth regulation in greenhouse production. PhD diss. Univ. of Georgia Athens GA
BayerA.MahbubI.ChappellM.RuterJ.van IerselM.W.2013Water use and growth of Hibiscus acetosella ‘Panama Red’ grown with a soil moisture sensor controlled irrigation systemHortScience48980987
BiermanP.M.RosenC.J.WilkinsH.F.1990Leaf edge burn and axillary shoot growth of vegetative poinsettia plants: Influence of calcium, nitrogen form, and molybdenumJ. Amer. Soc. Hort. Sci.1157378
BurnettS.E.PennisiS.V.ThomasP.A.van IerselM.W.2005Controlled drought affects morphology and anatomy of Salvia splendensJ. Amer. Soc. Hort. Sci.130775781
BurnettS.E.van IerselM.W.2008Morphology and irrigation efficiency of Gaura lindheimeri grown with capacitance-sensor controlled irrigationHortScience4315551560
CarvalhoS.M.P.HeuvelinkE.CascaisR.van KootenO.2002Effect of day and night temperature on internode and stem length in chrysanthemum: Is everything explained by DIFAnn. Bot. (Lond.)90111118
ChappellM.DoveS.K.van IerselM.W.ThomasP.A.RuterJ.2013Implementation of wireless sensor networks for irrigation control in three container nurseriesHortTechnology23747753
CliffordS.C.RunkleE.S.LangtonF.A.MeadA.FosterS.A.PearsonS.HeinsR.D.2004Height control of poinsettia using photoselective filtersHortScience39383387
FaustJ.E.HeinsR.D.1996Axillary bud development of poinsettia ‘Eckespoint Lilo’ and ‘Eckespoint Red Sails’ (Euphorbia pulcherrima Willd.) is inhibited by high temperaturesJ. Amer. Soc. Hort. Sci.121920926
FaustJ.E.KorczynskiP.C.KleinR.2001Effects of paclobutrazol drench application dates on poinsettia height and floweringHortTechnology11557560
FernandezR.J.WangM.ReynoldsJ.F.2002Do morphological changes mediate plant responses to water stress? A steady-state experiment with two C4 grassesNew Phytol.1557988
FrenschJ.HsiaoT.C.1995Rapid response of the yield threshold and turgor regulation during adjustment of root growth to water stress in Zea maysPlant Physiol.108303312
GarlandK.F.BurnettS.E.DayM.E.van IerselM.W.2012Influence of substrate water content and daily light integral on photosynthesis, water use efficiency, and morphology of Heuchera americanaJ. Amer. Soc. Hort. Sci.1375767
HammondH.E.SchoellhornR.K.WilsonS.B.NorciniJ.G.2007Differing blanket flower cultivar and ecotype responses to plant growth regulatorsHortTechnology17552556
KiehlP.A.LielJ.H.BuergerD.W.1992Growth response of Chrysanthemum to various container medium moisture tensions levelsJ. Amer. Soc. Hort. Sci.117224229
LatimerJ.G.LewisP.ThomasP.A.1999Plant growth regulator effects on height and landscape performance of perennial bedding plantsActa Hort.5048391
LewisK.P.FaustJ.E.SparkmanJ.D.GrimesL.W.2004The effect of daminozide and chlormequat on the growth and flowering of poinsettia and pansyHortScience3913151318
MilksR.R.FontenoW.C.LarsonR.A.1989Hydrology of horticultural substrates: II. Predicting physical properties of substrate in containersJ. Amer. Soc. Hort. Sci.1145356
MoeR.FjeldT.MortensenL.M.1992Stem elongation and keeping quality in poinsettia (Euphorbia pulcherrima Willd.) as affected by temperature and supplementary lightingSci. Hort.50127136
MurrayJ.D.Lea-CoxJ.D.RossD.S.2004Time domain reflectometry accurately monitors and controls irrigation water applications in soilless substratesActa Hort.6337582
NiuG.RodriguezD.S.RodriguezL.MackayW.2007Effect of water stress on growth and flower yield of Big Bend bluebonnetHortTechnology17557560
NiuG.RodriguezD.S.WangY.2006Impact of drought and temperature on growth and leaf gas exchange of six bedding plant species under different greenhouse conditionsHortScience4114081411
O’MearaL.van IerselM.W.ChappellM.R.2014Water use of Hydrangea macrophylla and Gardenia jasminoides in response to a gradually drying substrateHortScience49493498
PaceP.F.CralleH.T.El-HalawanyS.H.M.CothrenJ.T.SensemanS.A.1999Drought-induced changes in shoot and root growth of young cotton plantsJ. Cotton Sci.3183187
RavivM.WallachR.SilberA.Bar-TalA.2002Substrates and their analysis p. 25–101. In: Savvas D. and H.C. Passam (eds.). Hydroponic production of vegetables and ornamentals. Embryo Publ. Athens Greece
SharpR.E.2002Interaction with ethylene: Changing views on the role of abscisic acid in root and shoot growth responses to water stressPlant Cell Environ.25211222
van IerselM.W.ChappellM.R.Lea-CoxJ.2013Sensors for improved efficiency of irrigation in greenhouse and nursery productionHortTechnology23735746
van IerselM.W.DoveS.KangJ.G.BurnettS.E.2010Growth and water use of petunia as affected by substrate water content and daily light integralHortScience45277282
ZhenS.BurnettS.E.DayM.E.van IerselM.W.2014Effects of substrate water content on morphology and physiology of rosemary, Canadian columbine, and cheddar pinkHortScience49486492