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  • Author or Editor: Joe J. Hanan x
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Paul Read, ASHS Education Division Vice President, encouraged a number of us to share our thoughts on the teaching process for the edification of others. Among the courses I have taught over the last 20 years, a course on greenhouse management, including graduate level plant environmental measurements, has engaged my principal effort for the past decade. I have no pedagogical credentials to do so (i.e., teaching certificate), and certainly an educationist of today would consider me hopelessly old-fashioned and unqualified. However, I take solace in the face that Plato, Diogenes, and Confucius—to mention a few—did not have teacher training, computer grading, slide projectors, or television to “improve” information transfer. This probably represents the height of hubris to call upon the shades of some of the greatest teachers in history.

Open Access
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In 1963, we were not certain what constituted an adequate water supply for growth (53). A revolution of terminology and methods has occurred since, but I have the impression that horticulturists have been slow to accept the changes and the challenges these new approaches offer. As a result, the expertise peculiar to practicing horticulturists has, in turn, often been ignored.

Open Access
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Ethylene (C2H4) is a by-product of combustion, regardless of precautions taken to ensure complete burning. To avoid crop damage in greenhouses where burning is used to supply CO2, flue gases must be diluted. Tests in different greenhouses in the Denver region showed that C2H4 may reach significant levels in flue gases from large unit heaters vented into the house–unless the unit is equipped with a distribution tube to force complete air recirculation, bringing fresh air to the burner. The free air entry for combustion should be double the National Fire Protection Code requirements ca. 1 cm2 100 kcal−1hr−1 (2 in2 per 5000 BTU hr−1), and specific provision should be made in the greenhouse structure for combustion air entry.

Open Access
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Petal surface temperatures and temperature differentials between the petal surfaces and air, and between the petal surfaces and bottom of the calyx of fully open, red and white Dianthus caryophyllus flowers were examined under a variety of environmental conditions and transparent covers with the aid of an infrared thermometer. A number of multiple linear regression analyses were run on the data. Under certain conditions of wind velocity, solar radiation and air temperature, differentials of red carnation flowers exceeded 10° C, whereas white flowers were close to ambient air temperature. Lower radiant energy transmission by a cover reduced the effect of radiation level upon flower temperature, but increased petal surface temperatures and the differential between the petal surfaces and bottom of the flower. The differences were sufficient to partially explain results obtained in actual practice, to identify undesirable environmental parameters, and to emphasize a hitherto neglected area of research.

Open Access
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Abstract

Rosa hybrida L. cvs. Forever Yours and Cara Mia, were subjected to split night temperatures from November 1, 1977 to February 8-18, 1978. During the 22 weeks of treatment, split temperatures seriously delayed production and markedly reduced quality. Split temperatures for roses as a means of energy conservation did not appear to be a viable practice. Following the experiment, however, for a 9 week period, after returning night temperatures to 16.7°C, plants in the lowest temperature treatment produced twice as many flowers as compared to the entire previous record with a significant increase in quality and marked increase in bottom shoots. The effect appeared to be cumulative and suggested an inexpensive means for rejuvenating old rose plants.

Open Access

Abstract

The net rate of 14CO2 uptake was determined on individual leaves of Rosa hybrida, cv. ‘Forever Yours’, budded on Rosa manetti and grown in gravel. Rose leaves were found to reach an average peak of 11 mg CO2 dm−2 hr−1 about 6 days after the red color disappeared on the leaf underside, or 32 days after harvesting the previous flower on the parent cane. Thereafter, CO2 uptake declined during 14 days to 5 to 6 mg CO2 dm−2 hr−1. At ambient CO2 concentrations of 500 ppm, the maximum net uptake was near 3400 ft-c. However, internal plant water potential influenced the CO2 uptake by reducing it at each increase of radiant energy. This resulted in light saturation at lower energies the lower the plant water potential. Radiant energy affected both net CO2 uptake and water potential. Wilting was generally observed to occur at about –13 bars, and maximum rates of CO2 uptake were found at potentials of –8 bars or higher, over a range of 350 to 450 microeinsteins, or 3000 to 3500 ft-c.

Open Access
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Abstract

The benefits of an internal cover between a greenhouse roof and the crop, or a cover over the outside of a greenhouse, were developed on a theoretical basis. The analysis indicated that heat savings by the use of an internal shade will be the same on clear or cloudy nights, with the main effect resulting from lower convective losses. Therefore, an internal cover can be inexpensive as long as it reduces convective heat losses. An external cover can reduce thermal radiation losses from the greenhouse roof, and in this case, the emissivity of an external cover should be as low as possible. Radiation properties do not depend upon color. Calculations indicate that heat savings of internal and external covers are about the same under conditions of clear, winter nights. The potential savings with either cover alone approaches 30% of the present average greenhouse heat requirements.

Open Access

Abstract

Carnation (Dianthus caryophyllus L) cv Red Sim plants were treated with 100, 300 and 500 ppb C2H4 for varying durations at different growth stages. Carnations treated during rapid elongation (Stage III) were more susceptible to C2H4 than were plants treated at stages of less rapid growth (Stages I and IV). An effective dosage term (ppb-days) was used to correlate C2H4 concentration and exposure length. Although the highest dosages produced the greatest growth reduction, the rate of inhibition was higher at low dosages commonly found in metropolitan areas.

Open Access

Abstract

Carnations planted in November, 1965, were watered when soil moisture suction reached 0.04 bar, 0.6 bar and 10K ohms resistance (ca 20—50 bars), the latter measured with gypsum blocks. Yield was found to be highest for the 0.04 bar treatment. Mean grade was consistently higher for this treatment than the other 2 treatments throughout the flowering period. The results were mainly due to increased side shoots and longer internode lengths of cut flowers grown at suctions below 0.04 bar. Keeping life was reduced, but dye uptake was enhanced by growing carnations with frequent irrigations. Consumptive water use increased from 120.9 cm for the 10K ohm treatment to 184.7 cm for the 0.04 bar treatment, exceeding the water equivalent of solar radiation outside the greenhouse. However, there was no significant effect on water required per cut flower or on efficiency, whether the latter was based on total yield or dry weight. It was concluded that maximum production would occur where soil moisture stress is zero and internal plant stress is as close to zero as possible, provided other factors were favorable.

Open Access

Abstract

‘Forever Yours’ roses (Rosa hybrida L.) grown in 20-liter containers filled with gravel or soil, were irrigated with solutions of varying salinity and composition over a 2-year period. Results indicated that HCO3 ion was highly toxic to rose production, resulting in chlorosis whenever concentrations exceeded 2 meq liter−1. Sodium and Cl gave increasing problems above 4 meq liter−1. Sulfate was innocuous except as the ion contributed to total salinity of the solution. Yield was significantly reduced when electrical conductivity exceeded 1800 μmhos cm−1, and at 1300 μmhos cm−1 if ion proportions were adjusted. Treatments in soil were highly variable, with effects slower to appear.

Open Access