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Garry V. McDonald and Michael A. Arnold

The purpose of this study is to determine the effects of a variety of commonly used soil surface covers on the establishment of Cercis canadensis L. var. texensis (Wats.) Rose. `Alba'. Containerized 23.3-L trees were planted into 1.1 × 1.5-m plots separated by metal landscape edging in 20-cm-deep raised beds constructed of exterior treated landscape timbers. Eight soil surface treatments were imposed with five replicates each. Controls included bare soil with no cover. The remaining seven treatments consisted of 8-cm depth of pine bark mulch, Trachelospermum asiaticum (Siebold & Zucc.) Nakai on 30-cm centers mulched with 8 cm of pine bark, solid sodded Stenotaphrum secundatum (Walt.) Kuntze, 8 cm of decorative gravel, 3 cm of recycled paper mulch, brick pavers underline with 5 cm of coarse builders sand (brick-on-sand), and seasonal color mulched with 8 cm of pine bark. The color rotation for summer, fall / winter, and spring is Catharanthus roseus (L.) G. Don, Viola × wittrockiana Gams., and Petunia × hybrida Hort. Vilm.-Andr., respectively. Preliminary data indicates that mulching with pine bark resulted in similar or slightly increased trunk diameter growth over that of bare soil. Brick-on-sand and the recycled paper mulch had smaller increases in trunk diameter than the other treatments. Mid-day leaf water potentials of most treatments were similar to bare soil, but the mid-day water potentials of trees mulched with recycled paper were among the most negative. All treatments except brick-on-sand trees recovered as well or better than trees in the bare soil by the next morning. Poor predawn water potential recovery of brick-on-sand trees may be due to the elevated temperatures observed in their root zone. Bare soil, recycled paper mulch, and the annual treatments had the most negative soil moisture tensions on average. The bare soil may be due to increased evaporative loose over mulched soils. The large biomass of vinca as the season progressed may account for the more negative readings in the annual seasonal color plots.

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Garry V. McDonald* and Michael A. Arnold

Previous experiments indicated that plant growth regulators applied during greenhouse production can have a negative effect on subsequent landscape performance of pansy (Viola × wittrockiana H. Gams `Crown Yellow'). Three experiments were initiated in September 2003 to determine the affects of paclobutrazol and ancymidol on production and landscape performance of ornamental cabbage (Brassica oleracea L. var. acephala A.P. deCandolle `Dynasty Pink'), calendula (Calendula officinalis L. `Bon Bon Orange'), and pansy. Seeds were germinated in plug trays (1.5 cm3 inverted cone-shaped pockets) in a growth chamber with a 12 h photoperiod at 25/21 °C day/night. Plants were sprayed with paclobutrazol (formaulated as Bonzi) or ancymidol (formulated as Arest) at plug stage (cabbage, pansy, and calendula on 25 Sept., 2 Oct., 11 Nov., respectively), at 14 days after transplant into 0.73 L containers, or at both stages. Paclobutrazol was applied at 0, 5, 10 or 15 mg·L-1 and ancymidol at 0, 2, 4, or 8 mg·L-1. Cabbage (30 Oct.), pansy (6 Nov.), and calendula (4 Dec.) were transplanted to landscape beds to assess residual effects on growth and flowering. Cabbage and calendula, showed minor differences in growth during greenhouse production due to varying rates of either paclobutrazol or ancymidol, but exhibited a greater response to application time. Only minor differences in growth occurred with pansy during greenhouse production due to rate or time of application using ancymidol, but exhibited major differences in response to both rate and time of application using paclobutrazol. Residual effects on growth and flowering during landscape performance phase will be discussed.

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Garry V. McDonald and H. Brent Pemberton

Cut flower production in a low-input greenhouse for winter and spring holiday sales was evaluated. Low-input structure was a plastic covered Quonset greenhouse modified with sides that could be manually raised or lowered. Sides were raised on mild days for ventilation and remained closed for minimum heating for the few brief periods of sub-freezing temperatures characteristic of the local winter climate. Bulbs of tulip (Tulipa sp L.) cultivars `Maureen', `Negrita', and `Oxford' were dry cooled for 12 weeks and planted in December for Valentine's Day forcing. 30% shading did not significantly increase stem length in `Maureen' and `Oxford' but did increase stem length in `Negrita'. `Oxford' was at a harvestable stage for the. Valentine's Day market, but not `Maureen' or `Negrita'. All cultivars were of an acceptable quality. Plugs of snapdragon (Antirrhinum majus) cultivars `Appleblossom', `Potomac white', and `Rocket Rose' were planted in late winter at 4 and 6 inch spacing and were either pinched or not pinched. For all cultivars, pinching resulted in higher yield but lower grade. Four inch spacing had a slightly larger number of higher grade stems possibly due to stretching. `Appleblossom' and `Potomac White' were florist grade, whereas `Rocket Rose' was more appropriate for mass marker For both tulip and snapdragon, cultivar evaluation is necessary to determine suitable market strategy.

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Martin Meeks, H. Brent Pemberton, Lurline Marsh, and Garry V. McDonald

The effect of UV-B fluorescent lamp light on seedling elongation was investigated using three species: marigold (Tagetes sp.), cucumber (Cucumis sativa), and tomato (Lycopersicon esculentum). Seedlings were exposed to light supplied from two unshielded and unfiltered 40-watt UV-B fluorescent lamps. In two experiments, seedlings were placed a distance of 45 cm below the light for varying lengths of time, while seedlings were placed 60 cm below the light in a third experiment. For marigold, seedlings were shorter when germinated under the UV-B lamp than when germinated under natural light in a glasshouse. Two hours of exposure just after glasshouse germination (cotyledons unfolded) was effective in reducing height of cucumber seedlings, whereas 6 hours was required to significantly reduce the height of tomato seedlings. Treatments were still effective when the last measurements were taken 12 to 14 days after germination. Exposure of seedlings to UV-B lamp light provides a possible alternative means of preventing excessive seedling elongation instead of relying on chemical plant growth regulators.

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H. Brent Pemberton, Yin-Tung Wang, and Garry V. McDonald

Case-cooled bulbs of Lilium longiflorum `Nellie White' were potted on 4 Dec. 1995 and forced to flowering using standard growing procedures. Plants were illuminated from shoot emergence to visible bud with supplemental high-intensity-discharge sodium vapor light at 70 μmol·m–2·s–1 from 1700 to 2200 HR each day. When the first primary flower bud (first initiated flower bud most proximal on the shoot) was 5 to 7 cm long, each plant was treated with 3 ml of either de-ionized water or 500 mg·liter–1 6-(benzylamino)-9-(2-tetrahydropyranyl)-9H-purine (PBA). Sprays were directed at the flower buds and associated bracts. When the tepals on the first primary flower bud split, plants were placed at 2°C in the dark for 0, 4, or 21 days. After storage, plants were placed in a postharvest evaluation room with constant 21°C temperature and 18 μmol·m–2·s–1 cool-white fluorescent light. The first three primary flowers on PBA-treated plants lasted significantly longer than corresponding flowers on control plants, but there was no difference between flowers at the fourth and fifth positions. Also, the total postharvest life of the five primary flowers on PBA treated plants was 3 days longer than those on control plants. Storage time inversely affected the postharvest longevity of the first three primary flowers, but had no effect on the longevity of the fourth or fifth primary flowers or total postharvest life of the five primary flowers. There were no significant interaction effects between PBA treatment and storage duration on primary flower longevity.

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Michael A. Arnold, Garry V. McDonald, and Donita L. Bryan*

Most available information on the effects of planting depths for trees necdotal and/or testing of interactions with other important cultural practices implemented during landscape establishment is lacking. Green ash (Fraxinus pensylvanica H. Marshall, hypoxia tolerant species) and bougainvillea goldenraintree (Koelreuteria bipinnata Franchet, hypoxia intolerant species) were grown from seed in 2.3-L containers which were transplanted to 9.3-L black plastic and grown to a marketable size. Root-collars of the plants were maintained level with the surface of the substrate. Green ash (1 May 2001) and bougainvillea goldenraintree (27 Apr. 2001) were transplanted to clay soil field plots with the root-collars at a 7.6 cm above soil grade, at grade, or 7.6 cm below grade. Planting depths for each species were in factorial combinations with 0, 8, 15, or 23 cm of pine bark mulch covering 2.4 m2 of soil beneath each tree. After 2 years, survival of bougainvillea goldenraintrees planted below grade was one third that of those planted at or above grade. Planting below grade reduced survival of green ash by 25% after 3 years. Even the thinnest layer of mulch reduced bougainvillea goldenraintree height and trunk diameters. Height and trunk diameter responses interacted with planting depth for green ash. Mean soil moisture levels were slightly less negative with 8 cm of mulch (-5.8 kPa) compared to bare soil (-9.1 kPa), but increasing mulch thickness to 23 cm (-16.2 kPa) inhibited penetration of irrigation water/rainfall. This data suggests that planting with the root-collar at or above grade greatly enhances survival and growth potential of green ash and bougainvillea goldenraintree and that mulch application should be only at thin layers to inhibit weeds.

Open access

Garry V. McDonald and Wayne A. Mackay

The University of Arkansas Horticulture Department was charged in 2016 by university administration to develop and implement a student learning outcome (SLO)-based assessment plan. The Horticulture Department curriculum committee was tasked to develop such a plan. Various models were considered, but ultimately a modified plan based on the work of M.P. Pritts and T. Park was adopted. Adjustments were based on student population size and particular requirements that had to be integrated with the university-mandated SLO goals and objectives. Two phases of a student’s academic career were chosen to access: an incoming freshman or transfer phase and a late-term or degree completion phase. Specific learning outcomes and goals were identified as well as courses and activities that would reasonably be measured while meeting university requirements. Data collection on entering freshmen and transfer students started in Fall 2018. The full impact of the implemented plan will not be known until 2020, when the first full cohort of incoming freshmen reaches the terminal stage of the degree program.

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Garry V. McDonald, Michael A. Schnelle, and Michael A. Arnold

An emerging niche in landscape design is the creation of exotic venues in commercial and residential settings using unusual plant materials. For instance, the creation of a tropical looking pool area at a hotel, a southwestern desert look for a Mexican restaurant or an oasis for the consumer at a shopping venue can all be in part achieved by the addition of specific plants. Palms (Arecaceae) can be an important component of this effort, even in temperate landscapes. This article focuses on issues related to the incorporation of palms in temperate landscapes. Although palms are signature plants of tropical regions, a surprising number of species can be grown in U.S. Department of Agriculture cold hardiness zones 8, 7, or colder via a combination of appropriate genotype selection, attention to microclimates in design specifications, and/or special cultural practices to mitigate the impact of cold temperatures. Cold-tolerant palms can be a critical design element, especially when paired with other lush tropical-appearing plants, to achieve the goal of creating the illusion of an exotic tropical locale in temperate-climate landscapes. Genotypic and site specification, careful attention to establishment requirements, and modified maintenance practices are critical determinants for success that will be addressed.

Free access

H. Brent Pemberton, Yin-Tung Wang, Garry V. McDonald, Anil P. Ranwala, and William B. Miller

Case-cooled bulbs of Lilium longiflorum `Nellie White' were forced to flowering. When the tepals on the first primary flower bud split, plants were placed at 2 °C in the dark for 0, 4, or 21 days. After storage, plants were placed in a postharvest evaluation room with constant 21 °C and 18 μmol·m-2·-1 cool-white fluorescent light. Lower leaves, upper leaves, and tepals of the first primary flower from a concurrent set of plants were harvested for carbohydrate analysis using HPLC. Storage time did not affect carbohydrate levels in the lower leaf or tepal samples, but sucrose and starch levels decreased while glucose and fructose levels increased in the upper leaf tissue with increasing storage time. These changes were correlated with a decrease in postharvest longevity for the first four primary flowers. Longevity of the fifth primary flower and total postharvest life of the five primary flowers was unaffected by storage.

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Kyle R. Bading*, Garry V. McDonald, Michael A. Arnold, Wayne A. Mackay, and Jerry M. Parsons

Texas maroon bluebonnets (Lupinus texensis Hook. `Texas Maroon') grown for fall planting may be germinated as early as September. Plant growth regulators are commonly applied to control excessive stem elongation during production, but may potentially result in adverse responses in the landscape due to residual effects. In October 2003, an experiment was initiated to observe potential landscape residual effects of paclobutrazol (formulated as Bonzi) applied during the production phase to retard internode elongation. Seedlings were received in six-pack cell units. On 30 Oct. 2003, while still in six-packs, bluebon-nets were sprayed with paclobutrazol. Paclobutrazol was applied at concentrations of 0, 5, 10, and 15 mg·L-1 a.i. at a coverage rate of 10 mL per 0.93 m2. After treatment, half of the plants were transplanted from six-packs to 0.73 L pots and the other half remained in six-packs. Plants were grown in a nursery until they reached a marketable stage (13 Nov. 2003 for six-packs, 20 Nov. 2003 for 0.73-L pots). At the end of nursery production, one half of the plants (both container sizes) were then planted to landscape plots (0.3 m centers) at either College Station, Texas or Dallas, Texas. During the production phase, bluebonnets grown in 0.73-L pots had slightly larger growth indices than those produced in six-packs. As application rates of paclobutrazol increased, growth indices decreased. Possible residual effects on growth and flowering will also be discussed.