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Elizabeth Will and James E. Faust

A model was developed that will calculate the maximum number of containers that can be placed in a specified area. There are basically three patterns of container placement. First, “square” placement involves placing pots in parallel rows in both directions so that any four pots form a square. The other two methods involve staggered patterns in which any three containers form a triangle. In the “long staggered” pattern, the long rows are parallel to the long dimension of the bench or floor space, while in the “short staggered” pattern, long rows are parallel to the short dimension of the bench. Comparisons of spacing patterns were made using a range of greenhouse/bench dimensions and container sizes. In most cases, a staggered arrangement allowed a significant increase in the number of containers fitting on a bench as compared to square placement. For example, when 6-inch pots are placed pot-to-pot in an 8 × 50-foot greenhouse section or bench, “short staggered” or “long staggered” arrangement of containers permitted 10.4% to 11.9% more containers over that allowed by a square pattern. In general, the larger the bench or greenhouse section, the greater the benefit of staggered spacing. The difference between short and long staggered was usually less than 3%, and depended on the specific space dimensions. This model can be easily entered into a spreadsheet for growers to perform their own calculations.

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James E. Faust and Pamela Korczynski

In 1998, `Freedom Red' poinsettia stock plants were grown outdoors under 0%, 60%, and 80% shade cloth. The stock plants received a single pinch leaving 10 nodes below the pinch. Cuttings were harvested once per week for 3 weeks. The cuttings were propagated, transplanted, pinched, and grown to anthesis in the same greenhouses. After anthesis, the plants were dropped onto a concrete pad from increasing heights ranging from 10 to 70 cm. Stem breakage was recorded each time the plants were dropped. Stem breakage of the finished plants increased as the percentage of shade cloth over the stock plants increased and as cutting harvest week number increased. From the Week 1 cuttings, 0%, 8%, and 10% of the lateral stems broke off of plants from the 0%, 60%, and 80% shade cloth treatments when the plants were dropped 20 cm. From Week 2 cuttings, 6%, 30%, and 36% of the lateral stems broke off the 0%, 60%, and 80% shade treatments. From Week 3 cuttings, 0%, 29%, and 43% of the lateral stems broke off of the 0%, 60%, and 80% shade treatments that were dropped 20 cm. Thirty-six percent of the Week 3 cuttings broke off of the 80% shade treatment plants before anthesis, while none of the lateral shoots broke off of the 0% shade treatment until the plants were dropped from 40 cm.

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James E. Faust and Joanne Logan

The National Renewable Energy Laboratory developed the National Solar Radiation Database to provide accessible solar radiation data to the research community for various uses. Previously, we created a series of monthly daily light integral (DLI) maps to provide a tool for horticulturists to estimate the potential growth and flowering responses for various plants throughout the year. The original DLI maps were based on solar radiation data from 239 sites recorded from 1961 to 1990. The DLI maps presented in this article were created from an updated database that included data from 1998 to 2009. This database provides higher resolution data modeled from satellite images of cloud cover. The data are presented in pixels with each pixel representing 100 km2 of land across the lower 48 United States and Hawaii, whereas the Alaska data are 1600 km2 pixels. The database provided global horizontal irradiance data that were converted to DLI (mol·m−2·d−1) using the conversion factor of 0.007265 mol (400–700 nm)·Wh−1 (400–2700 nm), which assumes that 45% of the solar radiation is in the photosynthetically active radiation (PAR, 400–700 nm) region and 4.48 μmol·J−1 is the conversion from radiometric to quantum units. The updated DLI maps provide more geographically precise data reflecting recent weather patterns. We present a comprehensive review of recent research exploring the growth and flowering responses of horticultural crops to DLI.

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James E. Faust and Royal D. Heins

Quantum sensors were placed at plant canopy height inside and outside a glass greenhouse. Photosynthetic photon flux (PPF) was measured during September for a 3-hour period near sunrise and sunset, which were determined from US Naval Observatory Circular #171. Under clear skies, the PPF at the canopy exceeded 0.25 μmol·m-2·s-1 for nearly 20 minutes before sunrise through 20 minutes after sunset. Under heavy overcast, the duration was only 5 minutes before sunrise through 5 minutes after sunset. The PPF at the canopy reached 0.25 μmol·m-2·s-1 approximately 12 minutes later in the morning and 12 minutes earlier in the evening than it did outside the greenhouse. The length of the dark period perceived by plants in a greenhouse on September 21st (assuming plants perceive light at 0.25 μmol·m-2·s-1) can range from 11:37 (hr:min) during cloudy conditions to 11:15 during clear ones, a difference of 22 minutes. At 43°N latitude, the maximum difference in date of flower initiation because of an extended period of heavily overcast versus clear weather on a crop such as poinsettias would be one week since the night length during September increases by 3 minutes per day. The actual difference from year to year is probably less because a seven-day duration of heavily overcast weather is unlikely.

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James E. Faust, Elizabeth Will and Millie Williams

Graduate students received training in total crop management (TCM) techniques including pest scouting and trapping, nutritional monitoring, and graphical tracking of crop height. In 1995, one student visited five greenhouse businesses biweekly during the poinsettia (Euphorbia pulcherrima Willd.) season to provide TCM training to one greenhouse employee per business. In 1996, a second student visited one greenhouse business every week during the poinsettia crop to conduct the TCM program for that business. The students benefited from the gained practical knowledge of greenhouse production techniques and TCM techniques, and they also benefited from the opportunity to visit commercial greenhouses and interact with staff throughout the production cycle for an entire crop. This program also provided the students with the opportunity to develop their teaching, communication and training skills. The participating growers benefited during this study from receiving useful production information and TCM training. An evaluation of the program conducted in 1998 indicated that four of the five participating businesses continue to use some TCM techniques, while two of the five have fully integrated the TCM program into their normal production routines.

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James E. Faust and Royal D. Heins

The effects of temperature and irradiance on flower initiation and development were quantified to provide a basis for an inflorescence development model. The percentage of leaf axils forming an inflorescence increased as the daily integrated PPF increased from 1 to 4 mol m-2 d-1, while the rate of inflorescence development was a linear function of temperature from 18 to 26C. The appearance of a visible flower bud in the leaf axil was correlated with leaf blade length of the subtending leaf. Mathematical functions were used to describe leaf blade length at the time of visible flower bud as a function of temperature and irradiance, and also to describe the influence of temperature on the rate of leaf extension. The time of visible flower bud in the leaf axil was then predicted by measuring the current length of the subtending leaf blade and estimating the time required for the leaf blade to extend to the length required for visible flower bud appearance. A phasic development scale was used to describe the developmental status of an inflorescence from visible flower bud to anthesis. A model was then created which predicted time to anthesis based upon temperature and the current stage of inflorescence development.

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James E. Brown-Faust and Royal D. Heins

Saintpaulia ionantha `Utah' plants were grown in growth chambers at constant 15, 20, 25, and 30°C temperatures and daily photosynthetic irradiances of 1, 4, 7, and 10 mol1 m-2 day-1 delivered by 23, 92, 161, and 230 μmol m-2 s-1 for 12 hours. Models were developed describing leaf unfolding rate (LUR) and flower development rate (FDR) as a function of temperature and irradiance by recording the dates of leaf unfolding and flower opening over the course of the experiment and then calculating rates using regression. Both LUR and FDR increased as temperature increased from 15 to 25°C and then decreased. Both LUR and FDR increased as irradiance increased from 1 to 4 mol m-2 day-1. Increasing daily irradiance above 4 mol m-2 da y-1 did not significantly increase LUR or FDR. Model validation data are being collected from plants growing under 3 irradiance levels in greenhouses maintained at 15, 20, 25, and 30°C air temperatures.

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James E. Faust and Royal D. Heins

The effects of supplemental lighting on vinca (Catharanthus roseus L.) plant temperature were quantified in greenhouses maintained at air temperatures of 15. 25, and 35C. High-pressure sodium (HPS) lamps delivering 100 μmol·m-2·s-1 PPF provided 73 W · m-2 of total radiation (400 to 50,000 nm) to lighted plants. Plant shoot-tip temperature was measured by using 40-gauge thermocouples. Relative to air temperature, plant shoot-tip temperature depended on the irradiance and vapor-pressure deficit (VPD). Irrespective of VPD, the additional irradiance absorbed by plants under the HPS lamps increased plant temperature 1 to 2°C. Under relatively low VPD conditions (1 kPa), plant temperature was greater than air temperature, while under high VPD conditions (4 to 5 kPa), temperature of both lighted and unlighted plants remained below air temperature throughout the day. Temperature of lighted plants however, remained 1 to 2°C above that of unlighted plants. Analysis of a degree-day model of vinca development showed hastened development associated with supplemental lighting could be explained by increased plant temperature rather than any specific photosynthetic effect.

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James E. Faust and Royal D. Heins

Poor lateral branching sometimes occurs when certain poinsettia (Euphorbia pulcherrima) cultivars are pinched. Two experiments were conducted to determine the effect of high temperatures on axillary bud development. In Expt. 1, `Red Sails' plants were grown in a high-temperature environment (HTE) of 27°C at night (8 hr) and 30°C (3 hr), 33°C (10 hr), and 30°C (3 hr) in the day for two months, then transferred to a 20°C environment. In Expt. 2, plants grown at 20°C were transferred into the same HTE described above for 0, 2, 4, 8, 16, or 32 days and were then moved back into the 20°C environment. Axillary buds were examined for viability at the end of each experiment. In Expt. 1, only 8% of the lateral buds forming in the HTE were viable, while 80% of the buds forming in leaf axils of leaves unfolding after the plants were transferred to the 20°C environment were viable. In Expt. 2, 80% of buds produced in axils of the first four leaves to unfold after the start of the experiment were viable in all the treatments. However, the percentage of viable buds in the axils of leaf numbers 5 to 8 was 100, 100, 100, 96, 56, and 0 for the plants placed in the HTE for 0, 2, 4, 8, 16, and 32 days, respectively. These data indicate day temperatures of 30 to 33°C adversely affect lateral shoot development of `Red Sails' poinsettia.

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James E. Faust and Royal D. Heins

Dendranthema ×grandiflorm (Ramat.) Kitamura `Powerhouse' plants were pinched to five nodes and grown in growth chambers at 35C day temperature (DT) and 14,17,21,24, or 27C night temperature (NT) to determine if NT influenced lateral shoot development on plants exposed to high DT. Vegetative cuttings were removed from two successive flushes of lateral shoots and evaluated for lateral shoot development after rooting and subsequent apex removal. Lateral shoot development was determined on a third flush of shoots that developed on the stock plants. The percentage of nodes that developed lateral shoots on stock plants or vegetative cuttings was not related to NT. The percentage of first-order, second-order, and third-order axillary nodes that developed a lateral shoot on the stock plants, averaged over all NT, was 76, 65, and 12, respectively. The percentage of nodes that developed lateral shoots on the first-order and second-order cuttings was 29 and 19, respectively. We concluded that cool NT were ineffective in preventing a decrease in lateral branching on plants grown under high (35C) DT conditions.