Enhancing ornamental qualities of southern highbush blueberry container plants with paclobutrazol in subtropical climates

• PBZ at 46 mg·L⁻¹ enhances ornamental traits of southern highbush blueberries. • Reduced plant height improves adaptability for subtropical container gardening. • High PBZ doses alter fruit morphology, requiring careful application rates. • Findings expand ornamental blueberry options for diverse gardening markets. Interest in ornamental blueberries ( Vaccinium spp.) for container gardening is increasing, particularly among home gardeners seeking plants with both aesthetic appeal and edible qualities. However, the adaptability of current ornamental blueberry cultivars in subtropical regions is limited due to their moderate to high chilling requirements. This study aimed to enhance the ornamental qualities of southern highbush blueberry ( Vaccinium corymbosum L. interspecific hybrids) cultivars ‘Warm Land’ and ‘Biloxi’, which were not initially bred for ornamental use, through foliar application of paclobutrazol (PBZ). We investigated the effects of PBZ on controlling plant height, canopy spread, and fruit cluster characteristics on whips and laterals. Two field experiments were conducted in central Taiwan during the 2021–2023 season. In mid-September 2021, the first experiment involved treating ‘Warm Land’ plants with PBZ at 0, 4.6, 46, and 230 mg·L –1 . Although PBZ at 4.6 mg·L –1 did not affect the plant height, canopy spread, and plant-to-pot height, PBZ at 46 and 230 mg·L –1 significantly reduced these parameters by 17.1 %–33.6 %, 17.5 %–29.0 %, and 16.3 %–32.7 %, respectively, compared to the untreated control. The highest PBZ concentration also reduced the length of the main inflorescence axis and fruit number per fruit cluster on whips by 49.7 % and 31.5 %, respectively. In contrast, while the length of the main inflorescence axis on laterals was reduced, fruit number was not significantly affected. The second experiment in 2022 included both ‘Warm Land’ and ‘Biloxi’ and confirmed that PBZ effectively reduced plant height and altered fruit cluster characteristics without significantly affecting the canopy spread. Compared to the untreated control, higher PBZ concentrations (46 and 230 mg·L –1 ) significantly reduced the length of the main inflorescence axis on whips and laterals by 38.2 %–48.5 % and 20.0 %–40.0 %, respectively. Notably, at 230 mg·L –1 PBZ, compressed and deformed fruits were observed on whips. Although there was no significant reduction in the fruit number per cluster on whips, the fruit number per fruit cluster on laterals was significantly reduced by 26.2 % and 30.8 % at 46 and 230 mg·L –1 PBZ, respectively. Our results indicate that a single foliar application of 46 mg·L –1 PBZ effectively improves the ornamental qualities of ‘Warm Land’ and ‘Biloxi’ without negatively impacting the appearance of the fruits. This approach offers a cost-effective strategy to enhance ornamental traits of existing southern highbush blueberry cultivars and expands the use of ornamental blueberries in subtropical climates, thus diversifying the options available to home gardeners.