Temperature effects on the rate of flowering rose shoot development were previously modeled using a thermal units (heat units) approach. The current objective was to validate this model for three rose cultivars and to determine its suitability for use in rose production. Flowering shoots of `Cara Mia', `Royalty', and `Sonia' plants, grown in greenhouses at three temperature settings, were observed daily to determine when each of the following developmental events occurred: “harvest”, “bud break”, “unfolding of each leaf”, “visible flower bud”, and “shoot ready for harvest”. Each stage was defined to facilitate accurate, repeatable observations. Average hourly air temperatures were used in computing the accumulated thermal units (TU) required for shoots to develop from from one stage to the next. The base temperature (used in the TU computation) did not differ significantly among the cultivars; the value of 5.2C was used. Using these to predict the days on which the shoot was ready for harvest resulted in ±2 day accuracy for most shoots of `Royalty' and `Sonia' and ±2.5 days accuracy for most `Cara Mia' shoots. This indicates that this method is suitable for timing of rose crops and deciding on temperature set-points.
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