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After postharvest shipping, the lower leaves of zonal geranium (Pelargonium ×hortorum) cuttings often turn chlorotic and necrotic during rooting in a propagation environment. Our objective was to quantify the efficacy of spray applications of the plant growth regulators (PGRs) benzyladenine (BA) and/or gibberellic acid (GA) at various stages in propagation to reduce lower-leaf senescence and evaluate effects on subsequent rooting. In Expt. 1, cuttings of ‘Patriot White’ geraniums were harvested and treated with BA (2.5 or 5.0 mg·L⁻¹), BA + GA₄₊₇ (2.5 or 5.0 mg·L⁻¹ each), or GA₃ (0.5 or 2.0 mg·L⁻¹) either before or after a 2-day storage period simulating commercial shipping. Post-shipment application of all PGRs eliminated leaf yellowing compared with cuttings treated pre-shipment, but rooting was inhibited. In Expt. 2, the promotion of rooting from a rooting hormone preceding treatment with BA (1.25 to 5.0 mg·L⁻¹), BA+GA₄₊₇ (1.25 to 5.0 mg·L⁻¹ each), or GA₃ (0.25 to 2.0 mg·L⁻¹) was evaluated on ‘Patriot White’ geranium cuttings after a 2-day simulated shipping. Applying rooting hormones increased the percentage of fully rooted cuttings treated with BA and/or GA from 16.4% to 51.8%. In Expt. 3, cuttings of different geranium cultivars from a commercial producer varied in susceptibility and suppression of leaf yellowing after BA + GA₄₊₇ applications. We conclude that foliar applications of BA + GA₄₊₇ can suppress lower-leaf senescence and rooting during propagation of some geranium cultivars, and the inhibition of rooting can be at least partially overcome with an application of rooting hormone.

Many greenhouse growers have installed retractable energy curtains to reduce energy losses and heating costs. We performed experiments to quantify the effect of retractable nighttime curtains on plant shoot-tip temperature of New Guinea impatiens (Impatiens hawkeri Bull.) grown in glass-glazed greenhouses during winter. Plants were grown in separate greenhouses under different curtain materials and the following measurements were collected: plant shoot tip, aerial wet and dry bulb, and cover (glazing and superstructure or curtain) temperature; net canopy radiation (250 to 60,000 nm); transmitted shortwave radiation (SWR; 300 to 3,000 nm); and air velocity. At night, plants under an extended curtain had a higher (by 0.5 to 2.3 °C) shoot-tip temperature and the net longwave radiation (LWR_net; 3,000 to 100,000 nm) was 70% to 125% greater than plants without a curtain. Shoot-tip temperature was 0.2 to 0.6 °C lower under a shading curtain with open-weave construction (high air permeability) compared with closed-weave constructed curtains (e.g., blackout). As cover temperature decreased from 21 to 12 °C, measured shoot-tip temperature and LWR_net decreased by a mean of 3.0 °C and 39.1 W·m⁻², respectively. Under a vapor pressure deficit (VPD) of 0.4 to 0.9 kPa, plant shoot-tip temperature was a mean of 1.0 °C closer to dry-bulb temperature compared with plants under a VPD of 1.4 to 1.8 kPa as a result of decreased transpiration. During the day, shoot-tip temperature was 1.2 °C lower than dry-bulb temperature when transmitted SWR was less than 100 W·m⁻² and on average 1.6 °C higher than the dry-bulb temperature when SWR was more than 100 W·m⁻². Therefore, in addition to reducing greenhouse heating costs, a curtain extended at night over a crop of New Guinea impatiens could increase plant shoot-tip temperature and accelerate development.

Thirty herbaceous perennial species were treated at 5°C for 0 or 15 weeks. Critical photoperiods for flower initiation and development with and without a cold treatment were determined. Photoperiods were 10, 12, 13, 14, 16, or 24 hours of continuous light or 9 hours plus a 4-hour night interruption. Continuous photo-periodic treatments consisted of 9-hour natural days extended with light from incandescent lamps. Species were categorized into nine response types based on the effects of cold and photoperiod on flowering. Plants had three flowering responses to cold treatment: obligate, facultative, or none. The perennials were obligate long-day, facultative long-day, or day-neutral plants. For example, Campanula carpatica `Blue Clips' had no response to cold and was an obligate long-day plant requiring photoperiods of 16 hours or longer or night interruption for flowering. Rudbeckia fulgida `Goldsturm' had a facultative response to cold and required photoperiods of 14 hours or longer or night interruption for flowering. Veronica longifolia `Sunny Border Blue' had an obligate cold requirement and was day-neutral. Some species responded differently to photoperiod before and after cold. Leucanthemum ×superbum `Snow Cap' flowered as an obligate long-day plant without cold and as a facultative long-day plant after cold. Response categories are discussed.

Six obligate long-day species of herbaceous perennials were grown under six night-interruption treatments to determine their relative effectiveness at inducing flowering. Photoperiods were 9 hours natural days with night interruptions provided by incandescent lamps during the middle of the dark period for the following durations: 0.5, 1, 2, or 4 hours; 6 minutes on, 54 minutes off for 4 hours (10% cyclic lighting); or 6 minutes on, 24 minutes off for 4 hours (20% cyclic lighting). Response to night interruptions varied by species, but five of the six species flowered most rapidly and uniformly under 4-hour night interruption. Few or no Campanula carpatica `Blue Clips', Rudbeckia fulgida `Goldsturm', or Hibiscus ×hybrida `Disco Belle Mixed' plants flowered with 1 hour or less of continuous night-break lighting. All Coreopsis ×grandiflora `Early Sunrise' flowered, but flowering was hastened as the duration of night interruption increased. Echinacea purpurea `Bravado' flowered similarly across all treatments. In general, the effectiveness of the night-interruption treatments at inducing flowering was 4 hours > 2 hours > 20% cyclic > 1 hour > 10% cyclic > 0.5 hour.

Chrysanthemum (Chrysanthemum ×morifolium) is a common ornamental crop with a qualitative short-day flowering response. Extending a short day with moderate blue [B (400–500 nm)] light inhibits flowering in greenhouse conditions with sunlight but does not indoors (without sunlight) under B + red [R (600–700 nm)] light or white light. We postulated that the contrasting responses to B light as a day extension depended on far-red [FR (700–800 nm)] light during the day, which is plentiful under sunlight but lacking indoors under B+R or white light-emitting diodes. To study this response in three chrysanthemum cultivars, we delivered indoor lighting treatments at two locations with an 11-hour main photoperiod of B, green [G (500–600 nm)], R, and FR light, where subscript values indicate the photon flux density (in µmol·m⁻²·s⁻¹) of each waveband: B₆₀R₁₂₀, B₆₀G₆₀R₆₀, and B₆₀R₆₀FR₆₀. After each short main photoperiod, plants received 0 or 4 hours of day-extension lighting of 60 µmol·m⁻²·s⁻¹ of B light (B₆₀). Under all treatments except B₆₀R₆₀FR₆₀ with day-extension B₆₀, it took ‘Chelsey Pink’, ‘Gigi Gold’, and ‘Gigi Yellow’ 13 to 17 days to reach the first visible inflorescence and 42 to 51 days to the first open flower. In contrast, plants grown under B₆₀R₆₀FR₆₀ with day-extension B₆₀ took 41 to 67 days to reach the first visible inflorescence with few plants developing open flowers. Plants were tallest at the first open flower and after 9 weeks of treatments when grown under B₆₀R₆₀FR₆₀ with day-extension B₆₀. These results indicate that the inclusion of FR light, but not G light, in the main photoperiod is necessary for day-extension B light to inhibit flowering in chrysanthemum. On the basis of these results and those of other studies, we postulate that the spectral dependence of flowering in chrysanthemum depends on whether and how the phytochrome photoequilibrium changes during the day. In particular, a sufficiently high daytime phytochrome photoequilibrium (e.g., under B+R and B+G+R light) could establish a predominant mode of floral signaling that prevents perception of subsequent B light as a long day.

In 1996 and 1997, eight cultivars of cold-treated field-grown Astilbe were grown in a 20 °C green-house with short days (SDs = 9-h natural days) or long days (LDs = 9-h natural days with night interruption with incandescent lamps from 2200 to 0200 hr) to determine how photoperiod influences flowering. Cultivars studied were Astilbe × arendsii Arends `Bridal Veil', `Cattleya', `Fanal', and `Spinell'; A. chinensis Franch. `Superba'; A. japonica A. Gray `Deutschland' and `Peach Blossom'; and A. thunbergii Miq. `Ostrich Plume'. Flowering percentage was highest (≥90%) for `Cattleya', `Deutschland', `Fanal', `Ostrich Plume', and `Peach Blossom', regardless of photoperiod. Photoperiod did not affect the time to visible inflorescence or flower number for any cultivar studied. The time from visible inflorescence to first flower took 27 to 36 days, irrespective of photoperiod. Time to flower varied by cultivar; `Deutschland' was the earliest to flower (31 to 41 days) and `Superba' was the last to flower (51 to 70 days). `Fanal' and `Ostrich Plume' flowered slightly but significantly faster (by 1 to 6 days) under LDs than SDs. For five cultivars, the inflorescence was taller under LDs than SDs. All cultivars reached visible inflorescence and flower significantly faster (by 1 to 15 days) in 1997 than in 1996.

This study investigated the preharvest carbohydrate status and postharvest ethylene action of unrooted shoot-tip cuttings of lantana ‘Dallas Red’ harvested at three times during the day (0800, 1200, and 1600 hr) in relation to subsequent leaf abscission, shoot apices blackening, and adventitious root formation. The cuttings harvested at various times during the day were stored in darkness at 20 ± 1 °C for 4 days in sealed polyethylene bags. The cuttings harvested at 0800 hr had lowest total nonstructural carbohydrate concentrations; however, the amount of ethylene production during postharvest storage was similar among harvest times and increased during the storage period. After 4 days of storage, 69% of the leaves of cuttings harvested at 0800 hr abscised, but only 22% and 8% of the leaves abscised in cuttings harvested at 1200 and 1600 hr, respectively. Application of 1-methylcyclopropene (1-MCP) increased ethylene production and suppressed leaf abscission regardless of the harvest time, but cuttings harvested at 0800 hr developed blackened shoot apices. Leaf abscission was negatively correlated with total nonstructural carbohydrate concentration in the leaves, but no relationship was found with ethylene production. These results indicate that a high endogenous carbohydrate status decreases the postharvest ethylene sensitivity in unrooted shoot-tip cuttings of lantana. Time of harvest influenced subsequent rooting response; however, 1-MCP application did not inhibit rooting. Among various storage treatments, the best rooting response was observed in cuttings harvested at 1600 hr and treated with 1-MCP. Therefore, significant improvement of postharvest storage quality in vegetative lantana cuttings could be achieved by harvesting cuttings late in the day and treating with 1-MCP.

This study was carried out to examine the effect of photosynthetic daily light integral (DLI) on the growth and flowering of cyclamen (Cyclamen persicum Mill. ‘Metis Scarlet Red’). Plants with six fully unfolded leaves were grown at 24/16 °C (12 h/12 h) under an 8- or 16-h photoperiod at a photosynthetic photon flux of 50, 100, 150, 200, and 300 μmol·m⁻²·s⁻¹, which provided seven DLIs: 1.4, 2.9, 4.3, 5.8, 8.6, 11.5, and 17.3 mol·m⁻²·d⁻¹. Days to first flower decreased from 133 to 75 as DLI increased from 1.4 to 17.3 mol·m⁻²·d⁻¹, although the acceleration of flowering was less pronounced when the DLI was greater than 5.8 mol·m⁻²·d⁻¹. Mean leaf and flower number increased from 8.7 to 28.0 and from 0 to 14.7, respectively, as DLI increased from 1.4 to 11.5 mol·m⁻²·d⁻¹, but there was no further increase under a DLI of 17.3 mol·m⁻²·d⁻¹. Total dry weight and net photosynthetic rate showed a similar trend as leaf and flower number. We conclude that supplemental lighting can accelerate greenhouse production of potted cyclamen under a low ambient DLI (i.e., less than 12 mol·m⁻²·d⁻¹).

Ethephon [(2-chloroethyl) phosphonic acid] is a plant growth regulator that releases ethylene on application and can abort flowers, stimulate branching, and inhibit stem elongation. Although ethephon is used as a foliar spray during the commercial production of many ornamental crops, its effectiveness as a drench has not been widely investigated. We performed experiments to quantify the effects of an ethephon drench on growth and flowering of a range of bedding plant and Narcissus cultivars and to assess the effect of lime on ethylene release from a peat substrate. A substrate drench of 0, 100, 250, or 500 mg·L⁻¹ ethephon was applied to 12 potted Narcissus cultivars at one location, and up to 200 mg·L⁻¹ was applied to 24 cultivars of bedding plants at three locations. Compared with untreated controls, ethephon generally reduced plant height at flowering and the effect increased with increased concentration. For example, Narcissus treated with a 250 mg·L⁻¹ ethephon drench had stems that were 20% to 40% shorter at the end of flowering than control plants. However, ethephon drenches generally caused a 2- to 3-day flowering delay, and two cultivars had a phytotoxic response. Among the bedding plants studied, a 100-mg·L⁻¹ ethephon drench suppressed plant height at flowering by greater than 30% in Catharanthus, Celosia, Dianthus, and Verbena, but by only 10% to 15% in Lobelia, Lycopersicon, and Tagetes. The drenches also delayed flowering in 10 of the 16 crops measured and decreased dry mass accumulation in all of the crops measured. Ethephon release from peat substrate became maximal ≈120 h after application and was dramatically increased by incorporation of dolomitic lime up to a rate of 9.5 kg lime per m³ of peat. Collectively, these studies show that ethephon substrate drenches inhibit stem elongation in a broad range of floriculture crops, but can also delay flowering and reduce biomass accumulation.

Most commercial markets require growers of poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch.) to produce plants within strict height specifications. Plant growthretarding chemicals (PGRs) are commonly used to limit internode extension, but in some countries, growers are being pressured to reduce chemical use. Recently, a photoselective film was developed that specifically reduces the transmission of far-red light [(FR), 700 to 800 nm], offering an alternative strategy for height control. Two complementary trials, one in the United Kingdom and one in the United States, showed that plants grown under the FR film for 10 to 12 weeks were ≈20% shorter than control plants growing under neutral density (ND) films transmitting a similar photosynthetic photon flux as the FR film. In the United Kingdom trial, the FR filter delayed time to 50% bract color and first visible cyathia by 6.0 and 3.5 days, respectively, but did not influence time to final harvest. In the United States trial, plants under the FR film had an average of 25% more axillary branches than those under the ND film. In addition, the effects of reduced red [(R), 600 to 700 nm] and blue [(B), 400 to 500 nm] light on internode length, plant biomass, and axillary branching were determined using other photoselective plastics. Compared with plants under the ND film, internode length was 9% or 71% greater in plants grown under environments deficient in B or R, respectively. Our results indicate that poinsettia is highly sensitive to the R: FR ratio, and that spectral manipulation has potential for height control of commercial poinsettia crops.