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Harry C. Kohl Jr.

Abstract

It is common knowledge that for a given cultivar of Easter lily, small bulbs grown at the same location as large bulbs produce fewer flowers when forced into bloom. In a recent test at U. C. Davis, as an example, 30 gram bulbs produced 4.5 flowers per plant, while 80 gram bulbs of the same variety grown and forced exactly the same produced 8.9 flowers per plant. Bulbs of intermediate weight produced an intermediate weight produced an intermediate number of flowers. Somewhat less well known is that the number of leaves produced by the single apex of the lily plant per unit time is likewise directly proportional to bulb size. In the experimental Work reported in this paper, for instance, he increase in leaf count in 100 days was found to be directly and linearly proportional to the bulb size (Figure 1).

Open access

Harry C. Kohl Jr.

Abstract

Water is in a ubiquitous position relative to the life processes and living plants. This must not be construed to mean that water is a plentiful commodity. As we will see it is not. We need to conserve it; and it is reasonable to assume that major advances in water conservation will come about through careful management, selection, and use of plants since most of the water used is transpired from them. Therein lies an opportunity and a responsibility for horticulturists to inform first themselves and then the community and its various private and public action agencies of what measures can be taken.

Open access

Harry C. Kohl Jr. and R. L. Nelson

Abstract

Two experiments were conducted to test the hypothesis that plants in the vegetative state would not succumb as rapidly to low light intensities if they had no phosphorous available as the resulting restriction in growth would permit stored photosynthate to be available for plant maintenance. The first used Peperomia obtusifolia ‘Variegata’ as the test plant. The rooted cuttings were received on December 22, 1965, and potted in propagator’s sand. They were grown in sand cultures to the surface of which a mineral nutrient solution was applied daily with the leachate allowed to drain away. The mineral nutrient solution contained in millimoles per liter, 5, 6, 1, and 1 of Ca(NO3)2, KNO3, KH2PO4, and Mg-SO4, respectively. Two ppm of Fe were added as a chelate (Fe 138) and trace elements were added as usual for a solution culture according to the recipe of Hoagland.

Open access

Richard H. Merritt and Harry C. Kohl Jr.

Abstract

Seedlings of Petunia hybrida ‘Snow Cloud’ and Pelargonium × hortorum ‘Red Elite’ and ‘Cardinal Orbit’ were grown to anthesis at day air temperatures of 27° ± 3°C (9 hr) and either 7° ± 3° or 18° ± 3° night air temperatures (15 hr). Petunia crop productivity (CP, grams of dry matter produced per square meter of crop) and crop productivity efficiency (CPE, percentage of photosynthetic photon flux incident on the crop stored in the form of crop dry matter) were the same at both temperature regimes from canopy closure to anthesis, but anthesis was delayed 10 days at 7°. Petunias grown at 7° had four more basal branches and were only one-third the height of petunias grown at 18° (12 vs. 37 cm). CP and CPE were 20% lower for geraniums grown at 7° compared to CP and CPE for geraniums grown at 18°. The geraniums grown at 7° flowered 3 weeks later, were more compact, and were 16 to 19 cm shorter than geraniums grown at 18°.

Open access

Richard H. Merritt and Harry C. Kohl Jr.

Abstract

Crop productivity efficiencies (CPE) of around 8% (the ratio of the dry weight gain of the crop to the potential to produce dry weight), were realized with petunias (Petunia hybrida Villm.), provided that the crop canopy was essentially closed at the beginning of the 9- to 12-day experimental periods and that there were many branches (sinks). This was found at either long or short photoperiods or at either a normal (15.6°C) or reduced (7.2°) temperature for the 16-hour night periods. Long photoperiods resulted in significantly increased CPE through increased size of the leaves before the crop canopy was closed. Elevated root temperature increased CPE after a sizeable number of lateral branches had formed.

Open access

Richard H. Merritt and Harry C. Kohl Jr.

Abstract

Seedlings of Petunia hybrida cv. Snow Cloud were subjected to root zone temperatures at the bottom surface of the pots of 15.6° to 19.4°C (NT) or 21° to 35° (HT) and photoperiods of 9 (SD) or 13 hr (LD) for 25 days in a eontrolled-environment chamber with air temperatures of 21° for 9 hr and 15.6° for 15 hr. HT × LD plants produced the largest total leaf area, largest main stem leaves, and most dry weight of all treatments; they were tallest and bloomed first, but had the fewest lateral branches. HT × SD plants developed the most lateral branches at the fastest rate and had a total leaf area, dry weight gain, and root development comparable to those of the LD treatments. NT × SD plants were the smallest. Crop productivity efficiency was determined to be NT × SD = 2.9%, HT × SD = 3.4%, NT × LD = 3.7%, and HT × LD = 3.9%.

Open access

Richard H. Merritt and Harry C. Kohl Jr.

Abstract

Geranium seedlings (Pelargonium × hortorum L.H. Bailey, ‘Mustang’) grown in 13 hr photoperiods were 23% taller due to stem and petiole elongation, had larger leaves, and prior to canopy closure had a higher crop productivity efficiency (CPE) than seedlings grown under 9 hr photoperiods. In general, the tallest plants were produced when grown with soil temperatures of 18°C. The highest weekly CPE attained was 3.8%.

Open access

Harry C. Kohl Jr. and Yoram Mor

Abstract

Three cultivars of Chrysanthemum × morifolium Ramat. were grown as pot plants in a greenhouse at either normal (15.6°C minimum) night temperature (NNT). or at lower (5.0° minimum and 7.1° average) night temperature (LNT) during the period of flower development. The leaf area index was kept at or above the critical for both groups following original pot-to-pot spacing by a gradual increase in spacing to the final commercial spacing. The LNT plants took longer to become salable plants. Increased spacing for the LNT plants purposely proceeded more slowly, resulting in less average space being occupied per day, so that the total bench space cost per pot was essentially the same for the LNT and NNT plants. Under the above conditions, it was found that dry weight gain per pot at LNT was as great as or greater than at NNT. The quality of the plants, which were harvested when commercially salable, was satisfactory at both LNT and NNT for ‘Mandarin’ and ‘Yellow Mandalay’. The quality of ‘Tip’ was poor at both LNT and NNT. The accumulation of dry matter as a function of photosynthetically active radiation was more efficient at LNT than at NNT.

Open access

Harry C. Kohl Jr. and Stephen P. Thigpen

Abstract

Evidence from 3 experiments supports the hypothesis that beyond the critical leaf area index (LAI), the rate of dry weight gain is the same for Chrysanthemum morifolium Ramat. cv. Bright Golden Anne grown at either normal (15.6°C) or low (5.6°) night temperature, providing that conditions during the 8 hour light period are the same. The term “critical LAI” is suggested as the LAI at which the curve for rate of dry weight gain as a function of LAI assumes a slope approaching zero. Hence, with appropriate management of LAI, the productivity per unit area of greenhouse devoted to this crop could be as great at 5.6° as at 15.6° night temperature, despite the delay of maturation for plants grown at low night temperature.