Growth retardants must be applied at the proper stage of plant growth in order to be effective. Most bedding plants will require the first application within 2-4 weeks after transplanting when conventional procedures are followed, i.e., seed are sown in flats and transplanted to cell packs. Generally, bedding plants will have no more than 4-6 true leaves at this stage. For plug-grown seedlings, the initial application of a growth retardant should be made before seedlings begin to elongate. Conditions affecting plant absorption of growth regulators.
Open stomates permit maximal absorption of the growth retardant.
Since water stress induces closing of stomates, plants should be fully turgid at the time of growth regulator applications. Number of applications. The number of growth retardant applications needed for controlling height will depend on greenhouse environmental conditions and cultivar vigor. Stem elongation will be enhanced under low light conditions, temperatures above 75oF, and high moisture regimes. On sunny days, daytime greenhouse temperatures commonly exceed night temperatures because of solar heating effects.