We evaluated preplant bulb dips in three commercial plant growth retardants [ancymidol (A-Rest), paclobutrazol (Bonzi), and uniconazole (Sumagic)] for height control in seven oriental hybrid lily (Lilium) cultivars (Aubade, Berlin, Casa Blanca, Muscadet, Sissi, Star Gazer, and Tom Pouce), and seven LA-hybrid lily [hybrids resulting from crosses between easter lily (Lilium longiflorum) and Asiatic hybrids] cultivars (Aladdin's Dazzle, Best Seller, Cebeco Dazzle, Royal Dream, Royal Parade, Royal Perfume, and Salmon Classic) grown in containers. A 1-min dip into a range of concentrations of each product was used to determine the optimum concentrations for height control. The results indicate that bulb dips, especially with uniconazole and paclobutrazol, can be a highly effective means of height control in hybrid lilies. Cultivars varied in their response to growth retardant treatments. In general, LA-hybrid lilies were much more responsive to the growth retardant treatments than oriental hybrids and required lower rates for comparable height control. Delays in flowering, increased bud abortion and leaf yellowing were observed only with high concentrations of uniconazole or paclobutrazol where the height reduction was also too excessive for a commercially acceptable crop.

Height control is a crucial element for successful production of containerized lilies (Lilium sp.). While it has long been known that pre-plant dips in chemical Plant Growth Regulators (PGRs) can be effective for height control, new active ingredients, new cultivars, and new classes of lilies have necessitated a re-examination of this technique for height control. Advantages of pre-plant PGR dips are time and labor savings, accurate dosages, reasonable cost and perhaps most important, legality (at least in the United States). Disadvantages are that the treatment is applied well before there is a known height excess and questions of disposal of the used dip solution (environmental concerns). In this work, we investigated several commercial products (ancymidol, paclobutrazole and uniconazole) and a range of concentrations on the Oriental hybrid cultivars 'Aubade', 'Berlin', 'Sissi', 'Stargazer', 'Tom Pouce' and 'Muscadet' and the LA's 'Royal Perfume', 'Best Seller', 'Royal Dream', 'Aladdins Dazzle', 'Salmon Classic' and 'Royal Parade'. From these experiments, we have determined that 1) bulb dips, especially with paclobutrazole and uniconazole, can be a highly effective means of height control, 2) LA hybrid lilies are much more sensitive than Oriental hybrids and require lower rates, 3) care to not overdose should be exercised in a commercial setting.