Herbaceous peony in warm climate: Modelling stem elongation and growers profit responses to dormancy conditions

• Herbaceous peonies cultivated in a warm climate region were stored in winter.
• More than 4000 data for various dormancy and germination conditions were used.
• Stem elongation responses to winter dormancy conditions were modelled.
• For the chilling temperatures 2 °C and 6 °C the results were close one to another.
• The optimal amount of chill units was determined for the maximum profit of growers.

We analysed the data collected for herbaceous peony cultivated in a warm climate region and stored in winter under three constant chilling temperatures. We used the quadratic regression model to describe the stem elongation responses to winter dormancy conditions, and the logistic function to describe the weekly stems elongation. The predicted maximal stem length from the first model was used as the input parameter for the second model. More than 4000 data for various (a) chilling constant temperatures during dormancy, (b) dormancy duration, and (c) germination duration, were used. The models were applied to determine the optimal number of chill units. For this purpose, two criteria were used in different versions of the model: the maximal stem length and the maximal profit of farmers. For the two chilling temperatures of 2 °C and 6 °C, the optimal values of chill units (in the models of a maximal stem length and maximal profit of farmers) are close to one another, and the values of a maximal stem length and maximal profit are significantly different. In the case of the third chilling temperature of 10 °C, the model failed to determine the optimal number of chill units. The method of inverse confidence intervals for testing the significance of the optimal number of chill units was used.