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The vegetatively propagated `Fire Kiss' clone of the hybrid Zygopetalum Redvale orchid has appealing potted-plant characteristics, including fragrant flowers that are waxy lime-green and dark maroon with a broad, three-lobed, magenta and white labellum. We performed experiments to quantify how temperature influenced leaf unfolding and expansion, time from visible inflorescence to flower, and longevity of individual flowers and inflorescences. Plants were grown in controlled-environment chambers with constant temperature set points of 14, 17, 20, 23, 26, and 29 °C and an irradiance of 150 μmol·m^-2·s^-1 for 9 h·d^-1. As actual temperature increased from 14 to 25 °C, the time to produce one leaf decreased from 46 to 19 days. Individual plants were also transferred from a greenhouse to the chambers on the date that an inflorescence was first visible or the first flower of an inflorescence opened. Time from visible inflorescence to open flower decreased from 73 days at 14 °C to 30 days at 26 °C. As temperature increased from 14 to 29 °C, flower and inflorescence longevity decreased from 37 and 38 days to 13 and 15 days, respectively. Data were converted to rates, and thermal time models were developed to predict time to flower and senescence at different temperatures. The base temperature was estimated at 6.2 °C for leaf unfolding, 3.5 °C for time to flower, and 3.7 °C for flower longevity. These models could be used by greenhouse growers to more accurately schedule Zygopetalum flowering crops for particular market dates.

Odontioda is a cool-growing, sympodial epiphytic genus of orchids originating from the Andes Mountains of South America. Several hybrids are commercially grown as potted flowering plants for their brightly colored flowers and compact growth habit. We quantified how constant and fluctuating day/night temperatures influenced inflorescence initiation, time from visible inflorescence (VI) to flower, and pseudobulb development. Odontioda George McMahon ‘Fortuna’ and Lovely Penguin ‘Emperor’ were grown at constant temperature set points of 14, 17, 20, 23, 26, or 29 °C and day/night (12 h/12 h) temperatures of 20/14, 23/17, 26/14, 26/20, 29/23, or 29/17 °C. Plants were grown in glass greenhouses under a 12-h photoperiod and a maximum irradiance of 500 μmol·m⁻²·s⁻¹. Within 6 weeks, heat stress symptoms such as leaf necrosis were observed on plants grown at a day temperature of 26 °C or greater regardless of the night temperature. After 20 weeks, 90% or greater of both clones had a VI when grown at a constant temperature of 14 or 17 °C. Plants grown at a constant temperature of 17 °C had the greatest pseudobulb diameter with a mean increase of 3.5 to 4.0 cm. In all treatments, a minimum pseudobulb diameter was required for uniform inflorescence initiation; pseudobulbs with a diameter of 5.5 cm or greater developed a VI in 93% of plants. Data for time from VI to open flower were converted to a rate, and a thermal-time model relating temperature with inflorescence development was developed. The base temperature and thermal time for VI to flower in George McMahon ‘Fortuna’ and Lovely Penguin ‘Emperor’ were estimated at −0.1 °C and 1429 °C·d⁻¹ and 0.8 °C and 1250 °C·d⁻¹, respectively. This information could be used by commercial orchid growers to assist in producing potted flowering Odontioda orchids for specific market dates.

Photosynthetic daily light integral (DLI) and temperature are two environmental factors that profoundly influence plant growth and development. Two common ornamental annual crops, salvia (Salvia splendens F. Sello ex Roem & Schult.) and marigold (Tagetes patula L.), were grown in glass greenhouses under a mean DLI of 5 to 25 mol·m⁻²·d⁻¹ at temperatures from 14 to 27 °C. Growth (e.g., plant dry weight at flowering) and flowering characteristics (e.g., time to flowering and flower number) were modeled in response to the mean daily temperature and DLI by using multiple regression analysis. The rate of progress to flowering of salvia and marigold was primarily influenced by the mean air temperature. For example, time from seedling transplant to flowering of salvia decreased from 42 days to 24 days as temperature increased from 15 to 25 °C, with a mean DLI of 10 mol·m⁻²·d⁻¹. Flower number and plant dry weight on the date of first flowering generally decreased with increasing temperature and decreasing DLI in both species. For example, marigold plants grown at 15 °C and a mean DLI of 25 mol·m⁻²·d⁻¹ were 2.45 times greater in dry weight, had 2.12 more flowers, and had 49% larger flowers at flowering compared with plants grown at 25 °C and a mean DLI of 5 mol·m⁻²·d⁻¹. The models can be used to predict the impact of changing light and temperature conditions on plant quality and flowering of these two crops.

Light-emitting diodes (LEDs) have the potential to replace high-pressure sodium (HPS) lamps as the main delivery method of supplemental lighting (SL) in greenhouses. However, few studies have compared growth under the different lamp types. We grew seedlings of geranium (Pelargonium ×hortorum), pepper (Capsicum annuum), petunia (Petunia ×hybrida), snapdragon (Antirrhinum majus), and tomato (Solanum lycopersicum) at 20 °C under six lighting treatments: five that delivered a photosynthetic photon flux density (PPFD) of 90 μmol·m⁻²·s⁻¹ from HPS lamps (HPS₉₀) or LEDs [four treatments composed of blue (B, 400–500 nm), red (R, 600–700 nm), or white LEDs] and one that delivered 10 μmol·m⁻²·s⁻¹ from HPS lamps (HPS₁₀), which served as a control with matching photoperiod. Lamps operated for 16 h·d⁻¹ for 14 to 40 days, depending on cultivar and season. The LED treatments defined by their percentages of B, green (G, 500–600 nm), and R light were B₁₀R₉₀, B₂₀R₈₀, B₁₀G₅R₈₅, and B₁₅G₅R₈₀, whereas the HPS treatments emitted B₆G₆₁R₃₃. Seedlings of each cultivar grown under the 90 μmol·m⁻²·s⁻¹ SL treatments had similar dry shoot weights and all except pepper had a similar plant height, leaf area, and leaf number. After transplant to a common environment, geranium ‘Ringo Deep Scarlet’ and petunia ‘Single Dreams White’ grown under HPS₉₀ flowered 3 days earlier than those grown under HPS₁₀, but flowering time was not different from that in LED treatments. There were no consistent differences in morphology or subsequent flowering among seedlings grown under HPS₉₀ and LED SL treatments. The inclusion of white light in the LED treatments played an insignificant role in growth and development when applied as SL with the background ambient light. The LED fixtures in this study consumed substantially less electricity than the HPS lamps while providing the same PPFD, and seedlings produced were of similar quality, making LEDs a suitable technology option for greenhouse SL delivery.

A technology for long-day (LD) lighting was evaluated for commercial production of ornamentals using a stationary high-pressure sodium (HPS) lamp with an oscillating aluminum parabolic reflector (rotating HPS lamp). We performed an experiment with four LD species (Campanula carpatica Jacq., Coreopsis grandiflora Hogg ex Sweet, Petunia ×hybrida Vilm.-Andr., and Rudbeckia hirta L.) to compare the efficacy of a rotating HPS lamp in promoting flowering with night-interruption (NI) lighting using incandescent (INC) lamps. Seedlings were grown under natural short-day (SD) photoperiods (12 h or less) and NI treatments were delivered from a 600-W rotating HPS lamp mounted at one gable end of the greenhouse or from INC lamps that were illuminated continuously for 4 h or cyclically for 6 min every 30 min for 4 h. Plants were grown at lateral distances of 1, 4, 7, 10, or 13 m from the rotating HPS lamp, which provided a maximum photosynthetic photon flux of 25.4 μmol·m⁻²·s⁻¹ (at 1 m) to 0.3 μmol·m⁻²·s⁻¹ (at 13 m). Control plants were grown under an uninterrupted 15-h skotoperiod. Within 16 weeks, 80% or greater of the plants within each species that received NI lighting had a macroscopic visible flower bud or inflorescence, whereas all species but Petunia ×hybrida remained vegetative under the SD. Flowering of all species grown at 13 m from the rotating HPS lamp was delayed by 14 to 31 d compared with those under continuous INC. The weekly operational costs to provide NI lighting to a 139-m² greenhouse with one 600-W rotating HPS lamp or a standard cyclic INC lamp installation was estimated to be 80% to 83% lower compared with INC lighting for the entire 4-h NI. These results indicate that a rotating HPS lamp can be used to efficiently deliver LD lighting, but flowering time was delayed and flower number reduced in some species when the maximum NI light intensity was less than 2.4 μmol·m⁻²·s⁻¹.

Phalaenopsis orchids require a day temperature of 26 °C or less to initiate inflorescences, whereas the night temperature has little or no effect on inflorescence initiation. We determined the duration of high temperature required each day to prevent inflorescence initiation of four Phalaenopsis and Doritaenopsis clones. In Years 1 and 2, mature potted plants were grown in separate greenhouse sections with five daily durations at 29 °C: 0, 4, 8, 12, or 24 h. The high temperature was centered in the 16-h photoperiod (0600 hr to 2200 hr) and the remainder of the day was at 20 °C. Exposure to 29 °C for 8 h or longer inhibited inflorescence initiation of Phalaenopsis Miva Smartissimo × Canberra ‘Mosella’ and Phalaenopsis Brother Pink Mask × Brother Success ‘Explosion’, but Phalaenopsis Baldan's Kaleidoscope ‘Golden Treasure’ and Doritaenopsis ‘Newberry Parfait’ required exposure to 29 °C for 12 h or longer to inhibit inflorescence initiation. Flowering was completely suppressed only when high-temperature exposure time was continual for Doritaenopsis ‘Newberry Parfait’ and Phalaenopsis Baldan's Kaleidoscope ‘Golden Treasure’ and 12 h for Phalaenopsis ‘Mosella’. Plant leaf span generally increased as duration of exposure to 29 °C increased, but high-temperature exposure had few or no significant effects on flowering characteristics of flowering plants. These studies indicate that as few as 8 h of high temperature can prevent flowering of some Phalaenopsis hybrids, whereas others require greater than 12 h of high-temperature exposure.

Plant growth and architecture are regulated in part by light quality. We performed experiments to better understand how young plants acclimate to blue (B), green (G), and red (R) light and how those responses can be used to produce plants with desirable morphological characteristics. We grew seedlings of impatiens (Impatiens walleriana), salvia (Salvia splendens), petunia (Petunia ×hybrida), and tomato (Solanum lycopersicum) under six sole-source light-emitting diode (LED) treatments or one cool-white fluorescent treatment that each delivered a photosynthetic photon flux (PPF) of 160 µmol·m⁻²·s^–1 for 18 h·d⁻¹. Leaf number was similar among treatments, but plants grown under 25% or greater B light were 41% to 57% shorter than those under only R light. Plants under R light had 47% to 130% greater leaf area and 48% to 112% greater fresh shoot weight than plants grown under treatments with 25% or greater B. Plants grown under only R had a fresh shoot weight similar to that of those grown under fluorescent light for all species except tomato. In impatiens, flower bud number at harvest generally increased with B light, whereas in tomato, the number of leaflets with intumescences decreased with B light. This research discusses how light quality can be manipulated for desired growth characteristics of young plants, which is important in the production of specialty crops such as ornamentals, herbs, and microgreens.

Manipulating light quality is a potential alternative method of regulating plant height in the commercial production of ornamental crops. In particular, end-of-day (EOD) lighting with a high red (R; 600–700 nm) to far-red (FR; 700–800 nm) ratio (R:FR) can suppress extension growth, whereas a low R:FR can promote it. We investigated the effects of the R:FR and duration of EOD lighting in regulating extension growth and flowering of two poinsettia cultivars, White Glitter and Marble Star. Plants were grown at 20 °C under 9-hour days with or without EOD lighting provided by two types of light-emitting diode bulbs: R+white+FR (subsequently referred to as R+FR) and FR only. The R:FR ratios were 0.73 and 0.04, respectively, and the photon flux density between 400 and 800 nm was adjusted to 2 to 3 μmol·m⁻²·s^–1 at plant canopy. The six EOD lighting treatments were R+FR or FR for 2 or 4 hours, 2 hours of R+FR followed by 2 hours of FR, and 4 hours of R+FR followed by 2 hours of FR. We also investigated the impact of a 4-hour moderate-intensity (13 μmol·m⁻²·s^–1) EOD FR treatment in the second replication. EOD lighting generally increased poinsettia extension growth, with the greatest promotion under the longest lighting periods. There were no differences in days to first bract color and days to anthesis when the 9-hour day was extended by 2 hours, but flowering was delayed under 4- or 6-hour EOD treatments, except for the 2-hour R+FR + 2-hour FR and 4-hour FR treatments. Four hours of moderate-intensity EOD FR greatly promoted extension growth and delayed or prevented bract coloration in both cultivars. We conclude that EOD lighting promotes extension growth of poinsettia, and specifically, EOD FR at a low intensity (2–3 μmol·m⁻²·s^–1) is not perceived as long-day signal, whereas a higher intensity (13 μmol·m⁻²·s^–1) of FR delays flowering.

Volatile energy costs and lower profit margins have motivated many greenhouse growers in temperate climates to improve the energy efficiency of crop production. We performed experiments with dahlia (Dahlia ×hybrida Cav. ‘Figaro Mix’), French marigold (Tagetes patula L. ‘Janie Flame’), and zinnia (Zinnia elegans Jacq. ‘Magellan Pink’) to quantify the effects of constant and fluctuating temperatures on growth and flowering during the finish stage. Plants were grown in glass-glazed greenhouses with a day/night (16 h/8 h) temperature of 20/14, 18/18, 16/22 (means of 18 °C), 24/18, 22/22, or 20/26 °C (means of 22 °C) with a 16-h photoperiod and under a photosynthetic daily light integral of 11 to 19 mol·m⁻²·d⁻¹. Flowering times of dahlia, French marigold, and zinnia (Year 2 only) were similar among treatments with the same mean daily air temperature (MDT). All species grown at 20/14 °C were 10% to 41% taller than those grown at 16/22 °C. Crop timing data and computer software that estimates energy consumption for heating (Virtual Grower) were then used to estimate energy consumption for greenhouse heating on a per-crop basis. Energy costs to produce these crops in Charlotte, NC, Grand Rapids, MI, and Minneapolis, MN, for a finish date of 15 Apr. or 15 May and grown at the same MDT were estimated to be 3% to 42% lower at a +6 °C day/night temperature difference (DIF) compared with a 0 °C DIF and 2% to 90% higher at a −6 °C DIF versus a 0 °C DIF. This information could be used by greenhouse growers to reduce energy inputs for heating on a per-crop basis.

Supplemental radiation (SR), traditionally provided by high-pressure sodium (HPS) lamps, is recommended for greenhouse production of seedlings during radiation-limiting conditions. Light-emitting diodes (LEDs) have emerged as an appealing alternative to HPS lamps primarily because they can provide SR at improved energy efficiencies, they have longer fixture lifetimes, and the radiation spectrum can be tailored to potentially manipulate plant morphology by targeting radiation absorption of specific photoreceptors. We grew seedlings of three annual bedding plants and two vegetable transplants in greenhouses at 20 °C under a 16-h photoperiod under six SR treatments: five that delivered a photosynthetic photon flux density (PPFD) of 90 μmol·m⁻²·s^–1 from HPS lamps (HPS₉₀) or LEDs [four treatments composed of blue (B; 400–500 nm), red (R; 600–700 nm), far red (FR; 700–800 nm), and/or white LEDs] and one that delivered 10 μmol·m⁻²·s^–1 from HPS (HPS₁₀) lamps as a control with matching photoperiod. The LED treatments, defined by the percentages of B, green (G; 500–600 nm), and R radiation, were B₁₀R₉₀, B₄₅R₅₅, B₁₀G₅R₈₅, and B₁₂G₂₀R₆₈ + FR (FR at 12 μmol·m⁻²·s^–1). At transplant, leaf area and seedling height were similar among 90 μmol·m⁻²·s^–1 treatments in all species except snapdragon (Antirrhinum majus), in which seedlings grown under B₁₂G₂₀R₆₈ + FR had 62% greater leaf area than those grown under B₄₅R₅₅ and were 47%, 18%, 38%, and 62% taller than those grown under HPS₉₀, B₁₀R₉₀, B₁₀G₅R₈₅, and B₄₅R₅₅, respectively. After transplant and finishing under the same SR treatments, snapdragon flowered on average 7 days earlier under the B₁₂G₂₀R₆₈ + FR treatment than the other LED treatments, whereas geranium (Pelargonium ×hortorum) grown under B₄₅R₅₅ and B₁₂G₂₀R₆₈ + FR flowered 7 to 9 days earlier than those under the B₁₀G₅R₈₅ and B₁₀R₉₀ treatments. Seedlings of each species grown under the HPS₁₀ treatment accumulated less dry weight and took longer to flower compared with seedlings under the other SR treatments. We conclude that radiation quality of SR has relatively little effect on seedling growth and subsequent flowering although in some crops, flowering may be earlier when SR includes FR radiation.