Supplemental lighting is required for the production of high-quality vegetable transplants in greenhouses when the photosynthetic daily light integral (DLI) is low. Light-emitting diodes (LEDs) are a promising alternative to high-pressure sodium (HPS) lamps. However, there are a limited number of studies that have evaluated how LED supplemental lighting spectral quality beyond blue (B) and red (R) radiation influences plant growth and development. Seeds of hybrid greenhouse seedless cucumber ‘Elsie’ (Cucumis sativus), tomato ‘Climstar’ (Solanum lycopersicum), and pepper ‘Kathia’ (Capsicum annuum) were sown and placed into a dark growth chamber until radicle emergence. Seedlings were grown in a greenhouse at a 25 °C constant temperature set point and under five lighting treatments. The supplemental lighting treatments delivered a total photon flux density (TPFD) of 120 μmol·m−2·s−1 for 16 h·d−1 based on an instantaneous threshold from HPS lamps or LEDs [three treatments composed of B (400–500 nm), R (600–700 nm), white, and/or far-red (FR; 700–800 nm) LEDs], and a control that delivered 25 μmol·m−2·s−1 from HPS lamps (HPS25). The LED treatments defined by their wavebands (TPFD in μmol·m−2·s–1) of B, green (G, 500–600 nm), R, and FR radiation were B20G10R75FR15, B25R95, and B30G30R60; whereas the HPS treatments emitted B7G57R47FR9 (HPS120) and B1G13R9FR2 (HPS25). Generally, cucumber, pepper, and tomato transplants under B30G30R60 and HPS120 supplemental lighting had the greatest stem diameter. Fresh weight and leaf area of all three species was greater when G radiation replaced R or B radiation. For example, leaf area and fresh weight of cucumber, tomato, and pepper increased (by 33%, 22%, and 49%; and 35%, 14%, and 56%, respectively) for plants under B30G30R60 supplemental lighting compared with plants under B25R95 supplemental lighting. The most compact cucumber and pepper transplants were those grown under B25R95 supplemental lighting, and the most compact tomatoes were those grown under the HPS25 (control) and B25R95 supplemental lighting. Tomato transplants under treatments providing ≥30 μmol·m−2·s−1 of G radiation had an increased incidence of leaf necrosis. From this study, we conclude that plant responses to supplemental lighting quality are generally genera-specific, and therefore high-wire transplants should be separated by genera to optimize production and quality. However, additional studies are required to provide complete LED supplemental lighting recommendations.
Charlie Garcia and Roberto G. Lopez
Christopher J. Currey and Roberto G. Lopez
The influence of pre-plant bulb dips in paclobutrazol solutions on final plant height, days to flower, and flower bud number were evaluated for easter lily (Lilium longiflorum). ‘Nellie White’ easter lily bulbs were placed in solutions of paclobutrazol containing 0, 30, 60, or 120 mg·L−1 for 15 min preceding planting. Days to flower and flower bud number were unaffected by paclobutrazol. Plant height at flowering for bulbs dipped in paclobutrazol solutions was 15% to 26% shorter compared with untreated bulbs. Additionally, dipping bulbs in 120 mg·L−1 paclobutrazol resulted in plants that met target height specifications for commercially grown easter lily. Based on these results, dipping easter lily bulbs in paclobutrazol solutions can be an effective strategy for reducing stem elongation without negatively impacting days to flower or flower bud number for commercially grown easter lily.
W. Garrett Owen and Roberto G. Lopez
Variability in outdoor daily temperatures and photosynthetic daily light integrals (DLIs) from early spring to late fall limits the ability of propagators to accurately control propagation environments to consistently callus, root, and yield compact herbaceous perennial rooted liners. We evaluated and compared the effects of sole-source lighting (SSL) delivered from red (R) and blue (B) light-emitting diodes (LEDs) to supplemental lighting (SL) provided by high-pressure sodium (HPS) lamps on herbaceous perennial cutting morphology, physiology, and growth during callusing and initial rhizogenesis. Cuttings of perennial sage (Salvia nemorosa L. ‘Lyrical Blues’) and wand flower (Gaura lindheimeri Engelm. and A. Gray ‘Siskiyou Pink’) were propagated in a walk-in growth chamber under multilayer SSL provided by LEDs with [R (660 nm)]:[B (460 nm)] light ratios (%) of 100:0 (R100:B0), 75:25 (R75:B25), 50:50 (R50:B50), or 0:100 (R0:B100) delivering 60 µmol·m−2·s–1 for 16 hours (total DLI of 3.4 mol·m−2·d−1). In a glass-glazed greenhouse (GH control), cuttings were propagated under ambient solar light and day-extension SL provided by HPS lamps delivering 40 µmol·m−2·s–1 to provide a 16-hour photoperiod (total DLI of 3.3 mol·m−2·d−1). At 10 days after sticking cuttings, callus diameter and rooting percentage were similar among all light-quality treatments. For instance, callus diameter, a measure of growth, of wand flower cuttings increased from an average 1.7 mm at stick (0 day) to a range of 2.7 to 2.9 mm at 10 days after sticking, regardless of lighting treatment. Relative leaf chlorophyll content was generally greater under SSL R75:B25 or R50:B50 than all other light-quality treatments. However, stem length of perennial sage and wand flower cuttings propagated under SSL R50:B50 at 10 days were 21% and 30% shorter and resulted in 50% and 8% greater root biomass, respectively, compared with those under SL. The herbaceous perennial cuttings propagated in this study under SSL R50:B50 were of similar quality or more compact compared with those under SL, indicating that callus induction and initial rooting can occur under LEDs in a multilayer SSL propagation system.
Wesley C. Randall and Roberto G. Lopez
Annual bedding plant seedlings or plugs are considered high quality when they are compact, fully rooted transplants with a large stem caliper and high root dry mass. Greenhouses in northern latitudes rely on supplemental lighting (SL) from high-pressure sodium lamps (HPS) during winter months to achieve high-quality, finished plugs. Light-emitting diodes (LEDs) offer higher energy efficiencies, a long operating life, and precise waveband specificity that can eliminate wavebands not considered useful. Seedlings of Antirrhinum, Catharanthus, Celosia, Impatiens, Pelargonium, Petunia, Tagetes, Salvia, and Viola were grown at 21 °C under a 16-hour photoperiod of ambient solar light and SL of 100 μmol·m−2·s–1 from either HPS lamps or LED arrays with varying proportions (%) of red:blue light (100:0, 85:15, or 70:30). Height of Catharanthus, Celosia, Impatiens, Petunia, Tagetes, Salvia, and Viola was 31%, 29%, 31%, 55%, 20%, 9%, and 35% shorter, respectively, for seedlings grown under the 85:15 red:blue LEDs compared with those grown under HPS lamps. Additionally, stem caliper of Antirrhinum, Pelargonium, and Tagetes was 16%, 8%, and 13% larger, respectively, for seedlings grown under the 85:15 red:blue LEDs compared with seedlings grown under HPS lamps. The quality index (QI), a quantitative measurement of quality, was similar for Antirrhinum, Catharanthus, Impatiens, Pelargonium, and Tagetes grown under LEDs and HPS lamps. However, it was significantly higher for Petunia, Salvia, and Viola under 85:15, 70:30, and 100:0 red:blue LEDs than under HPS lamps, respectively. These results indicate that seedling quality for the majority of the species tested under SL from LEDs providing both red and blue light was similar or higher than those grown under HPS lamps.
W. Garrett Owen and Roberto G. Lopez
Under low-light greenhouse conditions, anthocyanin pigmentation in vegetative tissues of red- or purple-leafed floricultural crops is not fully expressed and, consequently, plants are not as visually appealing to consumers. Our objective was to quantify the effect of end-of-production (EOP; before shipping) supplemental lighting (SL) of different light sources, qualities, and intensities on foliage color of geranium (Pelargonium ×hortorum L.H. Bailey ‘Black Velvet’) and purple fountain grass [Pennisetum ×advena Wipff and Veldkamp (formerly known as Pennisetum setaceum Forsk. Chiov. ‘Rubrum’)]. Plants were finished under early (Expt. 1) and late (Expt. 2) seasonal greenhouse ambient solar light and provided with 16 hours of day-extension lighting from low-intensity light-emitting diode (LED) lamps [7:11:33:49 blue:green:red:far-red light ratio (%); control] delivering 4.5 μmol·m−2·s−1, or 16 hours of EOP SL from high-pressure sodium (HPS) lamps delivering 70 μmol·m−2·s−1, or LED arrays (100:0, 87:13, 50:50, or 0:100 red:blue) delivering 100 μmol·m−2·s−1, or 0:100 red:blue LEDs delivering 25 or 50 μmol·m−2·s−1. Geranium and fountain grass chlorophyll content and leaf color were estimated using a SPAD-502 chlorophyll meter and Minolta tristimulus colorimeter, respectively. Relative chlorophyll content (RCC) and foliage L* (lightness), C* (chroma; a measure of saturation), and h° (hue angle; a measure of tone) values were significantly influenced by EOP SL and days of exposure. Generally, RCC of geranium and fountain grass increased from 3 to 14 days of exposure to EOP SL from HPS lamps and LEDs delivering 100 μmol·m−2·s−1. Under low daily light integrals (DLIs) [8.6 mol·m−2·d−1 (geranium) and 9.4 mol·m−2·d−1 (purple fountain grass)] EOP SL providing 100 μmol·m−2·s−1 of 100:0, 87:13, 50:50, or 0:100 red:blue light for ≥14 days resulted in lower L* (darker foliage), C* (saturated), and h° (orange to violet-red hues). Our data indicate that a minimum of 14 days of EOP SL providing 100 μmol·m−2·s−1 of 50:50 or 0:100 red:blue light enhanced foliage color of geranium and fountain grass leaves when plants were grown under a low greenhouse DLI ≤ 9 mol·m−2·d−1.
W. Garrett Owen and Roberto G. Lopez
Under low-light greenhouse conditions, such as those found in northern latitudes, foliage of red leaf lettuce (Lactuca sativa L.) varieties is often green and not visually appealing to consumers. Our objective was to quantify the effect of end-of-production (EOP; prior to harvest) supplemental lighting (SL) of different sources and intensities on foliage color of four red leaf lettuce varieties, ‘Cherokee’, ‘Magenta’, ‘Ruby Sky’, and ‘Vulcan’. Plants were finished under greenhouse ambient solar light and provided with 16-hours of day-extension lighting from low intensity light-emitting diode (LED) lamps [7:11:33:49 blue:green:red:far red (control)] delivering 4.5 μmol·m−2·s−1, or 16-hours of EOP SL from high-pressure sodium (HPS) lamps delivering 70 μmol·m−2·s−1, or LED arrays [100:0, 0:100, or 50:50 (%) red:blue] delivering 100 μmol·m−2·s−1, or 0:100 blue LEDs delivering 25 or 50 μmol·m−2·s−1. Relative chlorophyll content (RCC) and foliage L* (lightness), and chromametric a* (change from green to red) and b* (change from yellow to blue) values were significantly influenced by EOP SL and days of exposure. Generally, RCC of all varieties increased from day 3 to 14 when provided with EOP SL from the HPS lamps and LEDs delivering 100 μmol·m−2·s−1. End-of-production SL providing 100 μmol·m−2·s−1 of 100:0, 0:100, or 50:50 red:blue light for ≥5 days resulted in increasing a* (red) and decreasing L* (darker foliage), b* (blue), and h° (hue angle; a measure of tone) for all varieties. Our data suggests that a minimum of 5 days of EOP SL providing 100 μmol·m−2·s−1 of 100:0, 0:100, or 50:50 red:blue light enhanced red pigmentation of ‘Cherokee’, ‘Magenta’, ‘Ruby Sky’, and ‘Vulcan’ leaves when plants are grown under a low greenhouse daily light integrals (DLIs) <10 mol·m−2·d−1.
Ariana P. Torres and Roberto G. Lopez
Current market trends indicate an increasing demand for unique and exotic flowering crops, including tropical plants. Tecoma stans (L. Juss. Kunth) ‘Mayan Gold’ is a tropical plant that was selected as a potential new greenhouse crop for its physical appearance and drought and heat tolerance. However, in winter and early spring, when propagation occurs, outdoor photosynthetic daily light integral (DLI) can be relatively low. The objective of this study was to quantify the effects of DLI during propagation of Tecoma and to determine optimum DLI levels for seed propagation. Seeds were propagated under 13 mean DLIs ranging from 0.75 to 25.2 mol·m−2·d−1 created by the combination of high-pressure sodium lamps (HPS) and fixed woven shadecloths of varying densities. Thirty-five days after sowing, height, stem diameter, node number, relative leaf chlorophyll content, leaf fresh weight, leaf number, total leaf area, individual leaf area, leaf area ratio, shoot and root dry mass increased as DLI increased. Average internode elongation and specific leaf area decreased at a quadratic and linear rate, respectively, as DLI increased from 0.75 to 25.2 mol·m−2·d−1. These experiments indicate that high-quality Tecoma seedlings were obtained when DLI was 14 to 16 mol·m−2·d−1 during propagation.
Roberto G. Lopez and Erik S. Runkle
Flowering potted orchids has become one of the largest segments of floriculture worldwide. Large-scale production of cuts or potted plants exists in China, Germany, Japan, The Netherlands, Taiwan, Thailand, and the United States. Despite the value of orchids, the flowering physiology of most orchid genera is not well described. Therefore, scheduling flowering crops for specific market dates (such as Easter or Mother's Day) is not possible for most genera. This paper summarizes world orchid production and reviews how environmental factors regulate growth and flowering of several commercially important orchid genera: Cattleya, Cymbidium, Dendrobium, Miltoniopsis, Phalaenopsis, and Zygopetalum. These genera primarily flower in response to relatively low temperatures, and, for some species and hybrids, flowering is promoted when the plants are also exposed to short photoperiods. Effects of light and temperature on growth and development are summarized for these genera, and implications for controlled production are discussed.
Madeline W. Olberg and Roberto G. Lopez
Due to the high cost associated with constructing and operating a greenhouse, many growers have begun using alternative, low-input methods for bedding plant production, such as unheated high tunnel and outdoor production. Previous research indicates that bedding plant production in unheated high tunnels may be suitable for cold-tolerant species, but flowering is delayed compared with greenhouse production. To our knowledge, there has been no published research on the effects of outdoor production on bedding plant species. The objectives of this study were therefore to 1) compare the growth and development of 10 cold-tolerant and intermediate annual bedding plant species grown in an unheated high tunnel or in an unprotected outdoor growing area, 2) evaluate the effect of a 1-week acclimation period in the high tunnel before outdoor production, and 3) quantify the effectiveness of these production methods for producing high-quality bedding crops. Seedlings of ‘Antigua Orange’ african marigold (Tagetes erecta), ‘Hot Cakes White’ stock (Matthiola incana), and ‘Lilac Flame’ primula (Primula acaulis), and rooted cuttings of ‘Aloha Kona Hot Pink’ calibrachoa (Calibrachoa ×hybrida), ‘Royal Lavender’ regal geranium (Pelargonium ×domesticum), ‘Bella Oceano’ lobelia (Lobelia erinus), ‘Potunia Plus Red’ petunia (Petunia ×hybrida), ‘Phloxy Lady Purple’ phlox (Phlox maculata), ‘Summertime Pink Charme’ osteospermum (Osteospermum ecklonis), and ‘Empress Purple’ verbena (Verbena ×hybrida) were transplanted on 13 Apr. 2015 (week 16) into an unheated high tunnel or an outdoor growing area, or into an unheated high tunnel for a 1-week acclimation period before being moved outdoors. Average mean daily air temperature was 2.3 °C lower outdoors compared with inside the high tunnel, whereas average daily light integral (DLI) increased by 11.7 mol·m−2·d−1. All plants were delayed when grown outdoors compared with in the high tunnel, and all marigolds grown outdoors died in April when outdoor air temperatures dropped below −4 °C. When plants were acclimated for a 1-week period before outdoor production, all species, with the exception of regal geranium, were delayed by less than 1 week compared with those grown in the high tunnel. Stem length of all species grown outdoors was reduced or similar to those in the high tunnel, whereas biomass accumulation and branch number was unaffected or increased for most species. Overall, high-quality bedding plants could be grown outdoors, although development may be delayed compared with high tunnel production. Growers must be aware of the risk of crop loss due to extreme temperatures and plan for delays when growing annual bedding plant crops outdoors.
Roberto G. Lopez and Erik S. Runkle
Prohexadione-Ca (ProCa) is a relatively new plant growth regulator (PGR) that inhibits internode length in rice, small grains, and fruit trees. However, little is known about its efficacy and potential phytotoxicity on floriculture crops and how it compares to other commercially available PGR chemicals. The effects of two foliar spray applications (2 weeks apart) of ProCa (500, 1000, or 2000 ppm), paclobutrazol (30 ppm), or a tank mix of daminozide plus chlormequat (2500 and 1000 ppm, respectively) were quantified on Dianthus barbatus L. `Interspecific Dynasty Red', Ageratina altissima R. King & H. Robinson (Eupatorium rugosum) `Chocolate', Lilium longiflorum Thunb. `Fangio', and Buddleia davidii Franch. `Mixed.' All plants were forced in a glass-glazed greenhouse with a constant temperature setpoint of 20 °C under a 16-h photoperiod. Two weeks after the second spray application of ProCa at 500, 1000, or 2000 ppm, plant height of Dianthus and Lilium was shorter than control plants by 56%, 60%, and 65% and by 6%, 26%, and 28%, respectively. However, ProCa bleached and reduced the size of Dianthus flowers. ProCa at 2000 ppm and daminozide plus chlormequat were effective at controlling the height of Eupatorium (64% and 53% reduction, respectively); however, leaves of Eupatorium were discolored and showed symptoms of phytotoxicity 1 week after the first ProCa application. Only daminozide plus chlormequat were effective on Buddleia. ProCa is an effective PGR for most of the crops we tested; however, its discoloration of red flowers and foliage may limit its application for commercial use.