Effects of pre-plant bulb soaks of flurprimidol and paclobutrazol and pre-plant bulb water soaks with basal root cutting on growth of three amaryllis (Hippeastrum) cultivars

Amaryllis (Hippeastrum) has been a popular potted bulb crop, that is available in an array of colors, including reds, whites, pinks, and bicolors. However, during greenhouse production, amaryllis plants grow relatively quickly and often become too tall and unstable due to their relatively large inflorescences. Two experiments were conducted to evaluate methods to control plant growth using three amaryllis cultivars; 'Matterhorn', 'Samba', and 'Olaf'. Experiments were conducted at Kansas State University (KSU) and Cornell University (CU). In experiment one, we evaluated the importance of removing or cutting basal roots in combination with pre-plant bulb water soaks on different plant growth parameters. Bulbs were subjected to six different treatments: 1) control (no trimming, no soak), 2) trimmed roots, no soak, 3) trimmed roots, 1 h soak, 4) trimmed roots, 12 h soak, 5) no trimmed roots, 1 h soak, 6) no trimmed roots, 12 h soak. Results showed that trimming roots and bulb soaks had no effect on 'Matterhorn' and 'Olaf', while trimmed basal root treatments delayed flowering and reduced inflorescence height in 'Samba'. A second study evaluated the effect of pre-plant plant growth regulator bulb soaks of flurprimidol and paclobutrazol at 100 mg L^-1 for 15, 30, or 60 min. All treatments reduced inflorescence height compared to the control for 'Olaf' at both locations, while there was no inflorescence height reduction for 'Samba', except for 60 min paclobutrazol soaks at KSU. Treatments did not affect flowering for 'Matterhorn' and 'Olaf', however resulted in decreased number of flowering plants in 'Samba'. The results obtained from these experiments demonstrate that trimming basal roots can reduce plant height and pre-plant bulb soaks can be effective in controlling plant height, however cultivar dependent.