Effect of low-temperature treatments on flowering in three cultivars of Hebe Comm. ex Juss.

Abstract

The genus Hebe is mainly native to New Zealand, and a number of species and cultivars are used as ornamental garden and balcony plants in many countries. The ornamental value is increased by controlled flowering. In this experiment chilling (15.5/9.5 °C or 9/3 °C day/night) treatments of different durations (0, 3, 6, 9 or 12 weeks) were tested on three cultivars of Hebe, ‘Inspiration’, ‘Variegata’ and ‘Waikiki’. After chilling the plants were forced under 25/19 °C conditions for 12 weeks. Flowering was promoted by the chilling treatments, and complete flowering in the apical shoots occurred after 9–12 weeks chilling in 15.5/9.5 °C for ‘Inspiration’ and ‘Waikiki’. Increased flowering of ‘Variegata’ (75% of the plants) was observed after 12 weeks 15.5/9.5 °C treatment followed by forcing. The more induced plants had become under the chilling treatments, the shorter time was necessary under the forcing conditions for flower development. With all cultivars, cool conditions were more effective for flower induction than cold conditions. Flowering was more rapid where the low temperature conditions lasted longest. Larger ‘Inspiration’ plants were induced more readily than the smaller plants. The importance of size of the plants at the start of chilling was tested for ‘Inspiration’, where plants with 22 nodes flowered after shorter time under forcing conditions than plants with 12 nodes. A cold treatment, at 9/3 °C, reduced the flowering intensity for ‘Inspiration’ and ‘Variegata’, while ‘Waikiki’ reacted unchanged. Without chilling only ‘Waikiki’ was able to develop flowers but in less than 50% of the plants.