The timing of the crop is probably the most important thing that Easter lily (Lilium longiforum thunb) forcers must accomplish, and the variable date of Easter complicates scheduling (6, 12). The influence of bulb maturity and treatments prior to being placed in the greenhouse, often not under the grower’s control, makes forcing a challenge (2, 11, 17). Several methods are used to monitor progress of the crop, but adjusting temperatures is the actual means of controlling the rate of growth and development. Measurements of time and temperature, expressed as heat units or degree-days, are used to monitor the growth and development of many crops (1, 13, 21) and to predict with a high level of precision certain stages of their development. Degree-days or heat units offer little advantage over time alone as indicators of crop progress under conditions where temperature can be controlled to eliminate or minimize variations. Variations in greenhouse temperatures, greater during daytime hours than at night, especially in southern U.S. locations, are largely responsible for timing problems with Easter lilies. Heat unit summations may be reliable indicators where such variations occur. There are apparently no reports of attempts to use heat units or degree-days to monitor Easter lily shoot development.
Plug production has increased the finished quality and uniformity of bedding plants, making them one of the most important greenhouse crops grown. The wide range of cultural practices used by different growers to produce plugs, may influence the efficacy of plant growth regulators applied to the same crop in postplug production. Ten bedding plant species were grown from plugs obtained from two sources using different cultural practices. The plugs were transplanted to jumbo six packs and sprayed with either chlormequat/daminozide tank mix, ancymidol, or paclobutrazol at three concentrations at three times of year. The effect of each plant growth regulator varied by plant species and time of year applied. Source of plug material did have a significant effect on height and time of flowering of finished bedding plants and the use of plant growth regulators did not minimize the differences in height between sources in most cases.
Eight bedding plant species were grown from plugs obtained from two sources. The plugs were transplanted into jumbo six packs and sprayed with a solution of chlormequat/daminozide with concentrations of 1000/800, 1250/1250, or 1500/5000 mg·L-1 when new growth was ≈5 cm in height or width. Three different species were grown in the fall (Dianthus chinensis L., `Telstar Mix', Petunia ×hybrida Hort. Vilm.-Andr., `Dreams Red', and Viola ×wittrockiana Gams., `Bingo Blue'), winter [Antirrhinum majus L., `Tahiti Mix', Matthiola incana (L.) R. Br., `Midget Red', and P. × hybrida, `Dreams Mix'], and spring [Catharanthus roseus (L.) G. Don, `Cooler Pink', Salvia splendens F. Sellow ex Roem. & Schult., `Empire Red', and Begonia ×semperflorens-cultorum Hort., `Cocktail Mix']. The treatments significantly reduced finished plant size of all species for each season. There was a significant difference in finish size between sources for Dianthus, Antirrhinum, Matthiola, Catharanthus, Salvia, and Begonia. The efficacy of chlormequat/daminozide also differed for each source of Dianthus, Matthiola, and Begonia, but the treatments minimized the differences in finish size between sources for Petunia and Viola. Chemical names used: (2-chlorethyl) trimethylammonium chloride (chlormequat); (N-dimethylaminosuccinamic acid) (daminozide).
Nitrate nitrogen has been recommended as the best form of nitrogen for the production of poinsettia while ammonium and urea have been reported to be deleterious to poinsettia growth. Recent studies have indicated that lower nitrogen and leaching levels will produce quality poinsettias. Poinsettias were grown with 21–7–7 Acid Special (9.15% NH4, 11.85% urea), 20–10–20 Peat-lite Special (7.77% NH4, 12.23% NO3), 15-220 plus Ca and Mg (1.5% NH4, 12.7% NO3, 0.8% urea), and 15–5–15 Excel CalMag (1.2% NH4, 11.75% NO3, 2.05% urea) applied at 200 mg·L-1. Plants were fertigated by drip irrigation with zero leachate. There were no significant differences between fertilizer treatments for plant height, width, bloom diameter, and dry weight. Electrical conductivity and pH did vary significantly between treatments; however, this did not effect plant growth. Thus, by using lower nitrogen levels and zero leachate, quality poinsettias can be grown with commercial fertilizers high in ammonium/urea or high in nitrate nitrogen, or ammonium and nitrate in combination.