Heartleaf brunnera (Brunnera macrophylla L.) is a popular herbaceous perennial that is often used in the landscape. With large leaves and a mounding habit, growth control is often needed during greenhouse production. Plant growth regulators (PGR) applied as substrate drenches or foliar sprays can control growth necessary to produce compact, high-quality containerized plants. Our objectives were to evaluate the efficacy and growth control provided by uniconazole substrate drenches or sprays. Rooted liners of heartleaf brunnera ‘Jack Frost’ were transplanted into containers (16.6-cm; 2.8 L) filled with a commercially formulated peat-based substrate. After 10 d, eight single-plant replicates received either a substrate drench or foliar application of uniconazole. For substrate drenches, 296-mL aliquots of solution containing deionized water (0 mg·L–1; control) or 0.25, 0.875, 1.75, 2,5, 5.5, 7.5, or 10.0 mg·L–1 uniconazole were applied across the substrate surface. For foliar sprays, 0, 2.5, 5.0, 7.5, 10.0, or 20.0 mg·L–1 uniconazole were applied at a rate of 1.89 L/ 9.29 m2. Plants were grown in a glass-glazed greenhouse at 23 °C under ambient daylight supplemented with a photosynthetic photo flux density of ≈120 µmol·m–2·s–1 delivered from light-emitting diode lamps from 0600 to 2200 HR (16-h photoperiod) to achieve a daily light integral of 14 mol·m–2·d–1. At 7 weeks after treatment, data were collected and plants were destructively harvested. In general, uniconazole significantly controlled plant height, diameter, and dry mass for each uniconazole application method. Plant height and diameter were 15% to 51% (2.2 to 7.6 cm) shorter and 22% to 40% (7.4 to 13.5 cm) smaller, respectively, than untreated plants as uniconazole drench concentration increased from 0.875 to 5.0 mg·L–1, respectively. Plants treated with 0.875 to 5.0 mg·L–1 developed 3 to 7 fewer leaves. Shoot dry mass was 39.5% lower than untreated plants as uniconazole drench concentration increased from 0.875 to 5.0 mg·L–1, respectively. For foliar applications, plant height and diameter were both reduced but to varying degrees. Plant height was reduced by 6% (~1 cm) but the greatest amount of control observed was in plant diameter which was reduced by 15 to 21% (4.8 to 7.2 cm) as concentrations increased from 5.0 to 10.0 mg·L–1. Collectively, these results indicate that drenches of 0.875 to 5.0 mg·L–1 uniconazole or foliar sprays of 5.0 to 10.0 mg·L–1 uniconazole may be used to control growth of ‘Jack Frost’ heartleaf brunnera.
