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Charlie Garcia and Roberto G. Lopez

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.

Free access

Madeline W. Olberg and Roberto G. Lopez

Heating accounts for up to 30% of total operating costs for greenhouse operations in northern latitudes. Growers often lower air temperatures for production to reduce energy costs; however, this causes delays in development even in cold-tolerant crops, such as petunia (Petunia ×hybrida). This delay increases production time and can reduce profitability. Recent studies on low air temperature bedding plant production indicate petunia as a strong potential candidate for using lower air temperatures in combination with bench-top root-zone heating (RZH) to avoid or reduce delays in development. The objectives of this study were to 1) quantify time to flower (TTF) of seven petunia cultivars and two recombinant inbred lines (RILs) when the mean daily air temperature (MDT) was lowered by 5 °C and bench-top RZH was used and 2) determine if a high-quality petunia crop can be produced on RZH. Petunia ‘Sun Spun Burgundy’, ‘Sun Spun Lavender Star’, ‘Sanguna Patio Red’, ‘Potunia Plus Red’, ‘Potunia Plus Purple’, ‘Supertunia Red’, ‘Supertunia Bordeaux’, and two RILs, IA160 and IA349, were grown in a greenhouse with an MDT of 15 °C without RZH or with a RZH set point of 21, 24, or 27 °C. Additionally, a commercial control (CC) was established by growing plants without RZH at an MDT of 20 °C. All plants were grown under a 16-hour photoperiod to provide a daily light integral (DLI) of ≈12 mol·m−2·d−1. Time to flower was shorter at higher RZH set points. For example, TTF of ‘Potunia Plus Red’ was 56, 52, 49, or 47 days for plants grown at an MDT of 15 °C without RZH, or with RZH set points of 21, 24, or 27 °C, respectively. When a RZH set point of 27 °C was employed, TTF of all cultivars and inbred lines, except ‘Potunia Plus Red’ and ‘Sanguna Patio Red’, was similar to plants grown in the CC. Shorter stem length, lower growth index, and smaller shoot dry mass (SDM) at flowering were observed for plants grown under lower air temperatures with RZH, resulting in a more compact and high-quality plant. Producing a compact plant in a shorter time period is beneficial for growers; thus, results suggest that MDT can be lowered to 15 °C for petunia production when a RZH set point of 27 °C is employed.

Free access

Roberto G. Lopez and Erik S. Runkle

In 2003, commercial greenhouse growers in the United States imported 724 million nonrooted cuttings valued at $53 million. During transit and storage, cuttings can be exposed to environmental stresses (e.g., low or high temperature), which can consequently decrease quality, rooting, and subsequent plant performance. We performed experiments to quantify how temperature and storage duration of cuttings influence root initiation, root number, lateral branch count and length, and time to flower of Tiny Tunia `Violet Ice' petunia (Petunia × hybrida hort. Vilm. -Andr.). Dry or wet cuttings were harvested and packaged into perforated bags within small, ventilated boxes and then into traditional shipping boxes. The boxes were placed in environmental chambers with temperature setpoints of 0, 5, 10, 15, 20, 25, or 30 °C for 0, 1, 2, 3, 4, or 5 d. Cuttings were then rooted in a propagation house at 26 °C with a vapor pressure deficit of 0.3 kPa under ambient photo-periods. The visual quality rating of dry packaged cuttings decreased with increasing temperature and shipping duration. After 2 d at ≥25 °C, cuttings were horticulturally unacceptable due to water stress and chlorophyll degradation and they never fully recovered. Dry- or wet-packaged cuttings held at temperatures of 0 to 30 °C formed significantly fewer roots and lateral branches as duration increased from 1–5 d. Although cuttings held for 5 d at 0 °C produced 60% fewer lateral branches, they subsequently flowered 5 d earlier than plants held at 0 °C for 1 d. Therefore, exposure to temperatures >15 °C for ≥3 d can reduce petunia cutting quality, delay rooting, and decrease plant size at flowering.

Free access

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.

Full access

Christopher J. Currey and Roberto G. Lopez

Total crop management (TCM) is a holistic approach to crop production that integrates data collection and interpretation to facilitate decisions that produce a uniform, high-quality, and marketable crop. Our objective was to determine if integrating TCM into poinsettia (Euphorbia pulcherrima) production experiences at two separate land-grant universities would improve student confidence in greenhouse potted plant production decision-making skills. Students produced containerized poinsettias and collected data on the greenhouse environment [light, temperature, and relative humidity (RH)], plant growth, media properties, irrigation water quality, and pest populations weekly at Purdue University (PU) (2011 and 2013) and Iowa State University (ISU) (2013) or biweekly (2015). Students were provided with self-assessments at the beginning and end of each course with statements about TCM and the various components comprising TCM activities. For nearly every statement at both institutions, self-assessments in confidence and understanding increased on the pre- to postsemester surveys. The systematic data collection combined with discussion and reflection provides an opportunity for peer instruction and learning. We believe TCM increases student confidence in their greenhouse plant production skills.

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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.

Free access

Roberto G. Lopez and Erik S. Runkle

Miltoniopsis orchids have appealing potted-plant characteristics, including large, fragrant, and showy pansylike flowers that range from white and yellow to shades of red and purple. Scheduling orchid hybrids to flower on specific dates requires knowledge of how light and temperature regulate the flowering process. We performed experiments to determine whether a 9- or 16-h photoperiod [short day (SD) or long day (LD)] before vernalization and vernalization temperatures of 8, 11, 14, 17, 20, or 23 °C under SD or LD regulate flowering of potted Miltoniopsis orchids. Flowering of Miltoniopsis Augres `Trinity' was promoted most when plants were exposed to SD and then vernalized at 11 or 14 °C. Additional experiments were performed to determine how durations of prevernalization SD and vernalization at 14 °C influenced flowering of Miltoniopsis Augres `Trinity' and Eastern Bay `Russian'. Plants were placed under SD or LD at 20 °C for 0, 4, 8, 12, or 16 weeks and then transferred to 14 °C under SD for 8 weeks. Another set of plants was placed under SD or LD at 20 °C for 8 weeks and then transferred to 14 °C with SD for 0, 3, 6, 9, or 12 weeks. After treatments, plants were grown in a common environment at 20 °C with LD. Flowering of Miltoniopsis Augres `Trinity' was most complete and uniform (≥90%) when plants were exposed to SD for 4 or 8 weeks before 8 weeks of vernalization at 14 °C. Flowering percentage of Miltoniopsis Eastern Bay `Russian' was ≥80 regardless of prevernalization photoperiod or duration. This information could be used by greenhouse growers and orchid hobbyists to more reliably induce flowering of potted Miltoniopsis orchids.

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Christopher J. Currey and Roberto G. Lopez

Plant growth retardants (PGRs) are commonly applied to control poinsettia (Euphorbia pulcherrima) stem elongation to meet a target final height. Two weeks after pinching, 4-fl·oz substrate drenches containing 0.0, 0.05, 0.10, 0.15, 0.20, or 0.25 mg·L−1 flurprimidol were applied to high-vigor ‘Orion’ and low-vigor ‘Polly Pink’ poinsettia (Expt. I); while drenches containing 0.0, 0.05, 0.10, or 0.15 mg·L−1 flurprimidol or a foliar spray containing 1250 mg·L−1 daminozide and 750 mg·L−1 chlormequat chloride were applied to high-vigor ‘Classic Red’ and low-vigor ‘Freedom Salmon’ poinsettia (Expt. II). Final height of ‘Orion’ and ‘Polly's Pink’ poinsettia was suppressed by 12% to 25% and 13% to 30%, respectively, as flurprimidol concentration increased from 0.05 to 0.25 mg·L−1. Final height of ‘Classic Red’ and ‘Freedom Salmon’ was suppressed by 11% to 30% and 10% to 19%, respectively, as flurprimidol concentration increased from 0.05 to 0.15 mg·L−1. Although the daminozide and chlormequat chloride spray had no significant effect on bract area index compared with untreated plants, bract area index was smaller for all plants treated with flurprimidol. However, the bract area to height ratio of all cultivars was not impacted by any PGR application, indicating aesthetic appearance was not negatively affected with smaller bract area. Time to anthesis was delayed by up to 4 days when 0.10 mg·L−1 was applied to ‘Classic Red’, although no significant delays were observed for the remaining cultivars. Based on these results, flurprimidol may be applied as an early drench to suppress height of poinsettia without adversely impacting finished plant quality or crop timing.

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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.

Free access

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.