Limonium × `Misty Blue' plants were treated with directed sprays of gibberellic acid (GA3) at 400 mg·liter–1 at weekly intervals. All GA3 treatments accelerated flowering and increased yield of flowering stems compared to nontreated plants. Treatment at 4 weeks after planting resulted in the greatest acceleration of flowering and increase in stem yield.
Rooted terminal cuttings and dormant 1-year-old transplants of Phlox paniculata L. `Ice Cap' and `Red Eyes' were cooled for 0, 4, 8, 12 or 16 weeks and forced under long-day photoperiod provided by incandescent lights as either a night-interruption (2200–0200 hr) or extended-day (1700–2200 hr). The influence of cooling duration, long-day lighting regime, and propagule type on forcing days to flower, flowering stem counts, and flowering stem length was evaluated in a 3 × 2 × 5 factorial experiment. Cooling accelerated flowering and increased stem yield and length. Days to flower for both cultivars decreased and flowering stems and length increased linearly as cooling increased from 0 to 16 weeks, regardless of lighting or propagule type, but cooling for 8 weeks or more was necessary to produce marketable cut flower stems. Extended-day lighting produced longer stems than night interruption, and stem counts were higher among plants grown from transplants, regardless of cooling duration, lighting regime, or cultivar. Flowering stems from rooted cuttings were generally longer than those from transplants. Cut flower stems of `Ice Cap' were longer than those of `Red Eyes', but days to flower and yields for the two cultivars were similar.
In two studies, rooted cuttings of Phlox paniculata L. ‘Ice Cap’ (summer phlox) were cooled for 0, 4, 8, 12, or 16 weeks. Plants were forced in a glasshouse averaging 18 °C nights under extended-day and night-interruption lighting from incandescent lamps providing a minimum of 14 μmol·s−1·m−2 at plant level or continuous lighting from metal halide (HID) lamps providing a minimum of 400 μmol·s−1·m−2 at plant level. The influence of cooling duration on forcing days to flower, flowering stem counts, and flowering stem length was evaluated. Cooling plants promoted longer stems, higher flowering stem yields, and decreased days to flower when forced under long days provided by incandescent lamps, but when forced under HID lamps, days to flower for cooled plants were similar to those of noncooled plants regardless of cooling duration. Phlox forced in extended daylighting flowered in fewer days, had longer stems, and produced more flowering stems than those forced in night-interruption lighting. With continuous HID lighting, stem lengths and stems harvested per plant increased in a linear manner as cooling increased from zero to 16 weeks. Stem lengths ranged from 63.6 cm for noncooled plants to 96.3 cm for those receiving 16 weeks cooling, and flowering stem yields ranged from seven stems per plant for noncooled plants to 13 for those cooled 16 weeks. Phlox forced under HID lights flowered in substantially fewer days and had longer stems than those forced under incandescent lamps.
The effect of cooling method and duration on off-season cut flower production of Lysimachia clethroides Duby was examined. Rhizomes harvested in October were cooled for 0, 4, 6, 8, 10, or 12 weeks at 4 ± 1 °C in crates with unmilled sphagnum peat moss or in 3.75-L pots filled with a commercial soilless medium prior to forcing in a warm greenhouse. After 6 or more weeks of cooling, shoots emerged from crates in higher percentages than from pots. However, only the duration of cooling, not the method, affected the rate of shoot emergence, visible bud formation, and anthesis of the first bud in the raceme. As cooling increased from 0 to 12 weeks, the greenhouse days required for shoot emergence, visible bud formation, and anthesis decreased linearly. The number of flowering flushes and flowering stems produced per plant varied quadratically with cooling duration, and the highest yields occurred when rhizomes received between 4 and 10 weeks of cooling. High numbers of flowers were produced rapidly after 10 weeks of cooling. As the number of successive flowering flushes increased, the stem length increased linearly while the stem diameter decreased linearly.
Gooseneck loosestrife (Lysimachia clethroides Duby) rhizomes were cooled for 10 weeks at 4 ± 1 °C prior to greenhouse forcing in continuous long days (LD); continuous short days (SD); 4, 6, 8, or 10 weeks of SD followed by LD until anthesis; and 4, 6, 8, or 10 weeks of LD followed by SD. None of the plants grown in continuous SD flowered, and fewer than 30% of plants flowered when grown in 4, 6, or 8 weeks of LD followed by SD for 21 to 25 weeks. At least 10 weeks of LD prior to SD were required to obtain 70% flowering. Plants receiving continuous LD or 4, 6, or 8 weeks of SD followed by LD flowered in the highest percentages (85% to 90%), but only 10% of plants receiving 10 weeks of SD followed by LD flowered. The number of greenhouse days required for visible bud formation and anthesis increased linearly as initial SD exposure increased, but the number of racemes produced by flowering plants was not affected. Plant height was greatest in continuous LD, and decreased linearly as initial SD exposure prior to LD increased from 0 to 10 weeks. Plants grown in continuous SD remained vegetative rosettes throughout the experiment, and their height increased linearly as initial LD prior to SD increased from 0 (continuous SD) to 10 weeks. These results demonstrate that supplemental LD lighting can promote growth and flowering in this species and that lighting can be discontinued 3 weeks before harvest of cut flower crops.
Five cultivars of the Angel Mist series of Angelonia angustifolia L. were evaluated in the Univ. of Georgia New Crop Program to determine the influence of temperature, irradiance, and photoperiod on crop growth and flowering. When the temperature was increased from 15 to 30 °C, days to visible bud and days to flower significantly decreased while height of flowers, vegetative height, and total height significantly increased. As irradiance increased, plant growth increased but little influence on flowering time was observed. Angelonia angustifolia appears to be a day-neutral plant with respect to flowering. The influence on growth regulators will also be discussed.
Five taxa of Helichrysum Mill. and Brachycome Cass. were recently evaluated for greenhouse production and amenity use. Preliminary studies on the influence of photoperiod, temperature, and growth regulators were conducted for H. bracteatum Vent., (syn Bracteantha bracteata) `Sunray' and `Matilda Yellow', H. apiculatum D.C, (syn Chrysocephalum apiculatum) `Golden Buttons' and Brachycome iberidifolia Benth. `Jumbo Mauve' and `Mauve Delight'. All taxa of Helichrysum were quantitative LD plants, flowering slightly more rapidly under night-break (2200-0200 HR) and extended day incandescent lighting, compared with 9-h short-day treatment. No influence of photoperiod occurred with cultivars of Brachycome. Constant temperature of 12, 20, or 28 °C were provided and all taxa demonstrated a linear decrease in flowering time as temperatures increased. The growth index (average of height and two measurements of width) was also influenced by temperature. Paclobutrazol and daminozide were applied at different concentrations and frequencies. Paclobutrazol was more effective than daminozide in both genera, and daminozide was ineffective in Brachycome.
Two studies were conducted to determine the influence of decapitation (pinch treatment) and photoperiod treatments on stem length, days from planting to harvest, and flowering stem yield in two delphinium cultivars. Plants of Delphinium ×belladonna Hort. ex Bergmans `Völkerfrieden' received a hard pinch (removal of apex and all stem and leaf tissue associated with leaves ≤10 cm), soft pinch (removal of apex and all stem and leaf tissue associated with leaves ≤4 cm), or no pinch. Plants of the D. elatum L. `Barbara' series were grown under either long- or short-day photoperiod, each treatment with or without receiving a soft-pinch. Time from planting to harvest was longer in pinched plants than in nonpinched plants of both cultivars regardless of photoperiod. Flowering stems were longer in hard- and soft-pinched plants of `Völkerfrieden' compared to nonpinched plants, and with `Barbara', stem length of pinched plants was either longer or similar to that of nonpinched plants regardless of photoperiod. At 30 days after the commencement of harvest, yield of flowering stems for hard-pinched plants of `Völkerfrieden' was higher than that for nonpinched plants, but yield from soft-pinched plants was similar to that for those not pinched. Stem yield for `Barbara' was higher for pinched plants under the long-day photoperiod, but under short days, yield from pinched plants was similar to that for those not pinched. Long days appear to increase yield and reduce production time in delphinium cultivars. Commercial benefits may be realized by growing nonpinched plants for earliness and pinched plants for longer stems and higher yield.