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Amir Rezazadeh and Richard L. Harkess

Purple firespike (Odontonema callistachyum), native to Central America, has potential for use as a new flowering potted plant. The effects of number of pinches (zero, one, or two) and number of cuttings (one, two, or three) per 6-inch pot were evaluated on the control of plant height. Plant height was suppressed as the pinch number increased. The greatest reduction was recorded with one cutting per pot and two pinches. The maximum number of branches per pot was recorded with two pinches and three cuttings per pot. In a second experiment, plant growth regulators (PGR) were also tested for efficacy of height control; 2 weeks after pinching, foliar sprays of paclobutrazol, flurprimidol, daminozide, chlormequat, and a tank-mix of daminozide + chlormequat or media drenches of paclobutrazol, uniconazole, or flurprimidol were applied. Plant height, leaf area, and leaf dry weight were recorded at 3, 6, and 9 weeks after PGR application. Maximum height control was obtained with uniconazole drench at 8 ppm, resulting in plants 22 cm tall, 61% shorter than the untreated control (56 cm); however, it resulted in severe leaf distortion. Plant height was 56% and 46% shorter than the control using drenches of paclobutrazol at 30 ppm and flurprimidol at 15 ppm, respectively. Daminozide spray at 2000 ppm and tank-mix of daminozide + chlormequat at 4500/1500 ppm suppressed stem elongation by 20.3% and 19%, respectively. Plants treated with paclobutrazol drench at 30 ppm reduced leaf area and leaf dry weight compared with other PGRs. Chlormequat spray at tested concentrations was ineffective for controlling firespike plant growth. The most attractive potted plants were produced using a drench application of paclobutrazol at 10 or 15 ppm.

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Mohammad Baqir and Richard L. Harkess

On 2 Feb. 1996, rooted cuttings of Pelargonium × hortorum L. H. Bailey cvs. Tango and Blues were planted in 750-cm3 (14 cm in diameter) pots containing peatmoss mixed with shredded tire rubber (2–6.0 mm particle size) at 0%, 20%, 40%, 60%, or 80%. Plants were irrigated by hand, drip, or ebb-and-fl ood, and were arranged in a split-plot experimental design. A wetting agent (Aqua Gro 2000 L, Aquatrols Corporation, Cherry Hill, N.J.) was mixed at the rate of 6 ml per 3750 ml of water and 120 ml of solution was applied to each plant. Greenhouse studies indicated that geraniums could be grown successfully in media containing up to 20% shredded tire rubber by volume when irrigated by hand. Plants grown in media containing more than 20% rubber were observed to be slow-growing and chlorotic. Tissue analysis of the plants indicated significantly increased levels of zinc in plants grown in media containing high percentages of rubber. Geraniums grown in media containing 80% rubber and irrigated using ebb-and-fl ood benches had the significantly highest levels of foliar zinc. Media porosity, percent air space, and bulk density increased, while water holding capacity decreased with increasing amounts of shredded tire rubber added to the media.

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Lynn Burney and Richard L. Harkess

Maintaining annual color throughout the long summer season in warm temperate regions has become an interest to landscapers and nursery operators. Some colorscaping companies have begun implementing a second summer planting season. There is little information available concerning suitable cultivars and species of bedding plants for establishment in late summer. This study examined plant establishment in two container sizes and three dates of transplanting to determine late season establishment in Starkville, Miss. (33°27' latitude, 88°49' longitude). Seeds of 27 different cultivars were grown in plug flats in the greenhouse and transplanted into jumbo 606 or 10-cm square containers. The plants were grown in the greenhouse until transplanting on 16 Aug., 30 Aug., or 13 Sept. 1996. The plants were transplanted into plots containing nine plants with three replications per planting date. The plants were spaced on 20-cm centers among and between plots. The earliest two plantings resulted in better plant establishment and floral display. Some of the cultivars and species were more tolerant of the late season temperature and humidity establishing and providing a good color display from 6 weeks after transplanting until frost, 2 Nov. 1996. Cultivars that performed well included: Impatiens wallerana `Deco Crystal', `Expo Lavender Blush', `Dazzler Salmon', Begonia semperflorens `Varsity Bronze Scarlet', Zinnia `White Pinwheel', Tagetes erecta `Marvel Gold', and Tagetes patula `Bonanza Harmony'. Cultivars that did not establish well under these conditions included: Verbena hybrida `Romance Pink' and Salvia splendens `Salsa Salmon'. The container size did not significantly affect plant establishment.

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Scarlett L. Walker and Richard L. Harkess

Flowering of Impatiens hawkeri Bul. during production results in an accumulation of dead plant material and directs energy away from vegetative growth. Ethephon is currently used at 500 ppm during the production of cuttings to eliminate flowering on stock plants. In this study, the timing and rate of ethephon application during production was examined. Two cultivars were used: `Innocence' and `Shadow'. Ethephon was adjusted to pH 5.0 and applied at planting (0), or 1, 2, 3, or 4 weeks after planting at 0, 250, or 500 ppm. An additional control of water adjusted to pH 5.0 was also included. Five replications were used in a completely randomized experimental design. The experiment was conducted twice—26 June 26 and 7 Oct.1995—each lasted 10 weeks. The number of branches, plant size, fresh:dry weight ratio, and days to first flower were recorded. `Innocence' did not significantly respond to the treatments, except for branch number and fresh:dry weight ratio, which decreased when treated with ethephon. In `Shadow', a treatment of ethephon at 250 ppm 1 or 3 weeks after transplanting provided the best control of flowering with a minimal delay in production and high plant quality.

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Amir Rezazadeh, Richard L. Harkess, and Guihong Bi

Red firespike (Odontonema strictum) is an ornamental shrub with potential for use as a flowering potted plant due to its dark green foliage and attractive red flower spikes. To stimulate branching and improve quality of red firespike, foliar spray applications of dikegulac sodium (DS) and benzyladenine (BA) and hand pinching were evaluated across two seasons (Spring and Summer 2014). There were three pinching treatments: one, two, or three pinches. Plant growth regulators (PGRs) were applied at 400, 800, 1600, or 2400 ppm DS or 600, 1000, 1250, or 1750 ppm BA. Both studies included an untreated control. Red firespike treated with all concentrations of BA and 1600 and 2400 ppm DS had increased branching compared with the control, except 1000 ppm BA in Expt. 1. Pinching did not affect the number of branches. Dikegulac sodium at 1600 and 2400 ppm and all concentrations of BA resulted in shorter plants than the control. Phytotoxicity was observed in plants treated with 1600 or 2400 ppm DS. In both experiments, DS at 1600 and 2400 ppm had the least plant dry weight compared with the control. Treatment with BA at 1750 ppm resulted in greatest leaf area compared with control. Dikegulac sodium at 800 ppm increased the number of flowers compared with control. Pinching and BA did not affect number of inflorescences. All concentrations of BA and DS delayed flowering, except 1000 ppm BA. Plants treated with 800, 1600, and 2400 ppm DS had shorter inflorescences compared with control plants. Benzyladenine decreased the length of the inflorescence at high concentrations, 1250 and 1750 ppm. Pinching treatments did not affect inflorescence length.

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James M. Rawson and Richard L. Harkess

Three experiments were conducted using Lagerstroemia `Victor' and `Zuni', one on pinching, another on photoperiod, and the third with fertilizer rates. Liners were potted with either one or three liners per container. In the pinching experiment, treatments were 0, 1, 2, 3, or 4 pinches at 0, 2, 4, or 6 weeks after planting. In the photoperiod experiment the plants were exposed to 0, 4, 8, or 12 weeks of short days before being moved to long days. In the fertilizer experiment the plants were fertilized at 0, 200, 400, 600, or 800 mg.L-1 nitrogen from 20-10-20 liquid feed and 0 or 6 g per container of 15-11-13 slow-release fertilizer. For both `Victor' and `Zuni', three liners per container resulted in plants that were wider and shorter than those with only one liner. Neither timing nor number of pinches significantly affected plant size. Short days prevented vegetative growth and floral development in both cultivars. `Victor' grew and flowered best after receiving 8 weeks of short days before moving to long days. `Zuni' grew and flowered best when moved directly to long days after potting. Both `Victor' and `Zuni' grew best when receiving either 200 mg·L-1 or 6 g of slow-release fertilizer.

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Richard L. Harkess and Robert E. Lyons

A study was undertaken to determine the rate of floral initiation in Rudbeckia hirta. R. hirta plants were grown to maturity, 14-16 leaves, under short days (SD). Paired controls were established by placing half of the plants under long days (LD) with the remainder left under SD. Beginning at the start of LD (day 0), five plants were harvested daily from each photoperiod group for twenty days. Harvested meristems were fixed in 2% paraformaldehyde - 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer (pH 7.0) for 24 hrs, dehydrated in an ethanol series, embedded in paraffin and sectioned at 8 μm. Serial sections were stained with Methyl-green Pyronin, with adjacent sections treated with RNase for nucleic acid comparison. All events of floral initiation were identified, The results of limited inductive photoperiod indicate that 16-18 LD were required for flowering.

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Tongyin Li, Guihong Bi, and Richard L. Harkess

Plant growth and nitrogen (N) uptake of Encore® azalea ‘Chiffon’ (Rhododendron sp.) grown in a traditional plastic container or a biodegradable container made from recycled paper were investigated over the 2013 growing season. Three hundred twenty 1-year-old azalea liners, grown in two types of containers, were fertilized twice weekly with 250 mL N-free liquid fertilizer with no N or 15 mm N from ammonium nitrate (NH4NO3). Biweekly from 10 May to 3 Dec., five plants from each N rate and container type were selected randomly to measure plant height, widths, and leaf chlorophyll content in terms of soil–plant analysis development (SPAD) readings, and were then harvested destructively for nutrient analyses. Leaf SPAD readings and tissue N concentration were influenced mostly by N rate rather than container type, with 15 mm N producing greater values than the no-N treatment. Leaf SPAD readings increased from May to August and decreased from September to December. Using 15 mm N, plastic containers generally resulted in similar or increased plant growth [plant growth index (PGI) and dry weight] and N uptake from May to August as in biocontainers, with greater SPAD readings, leaf and root dry weights, stem and root N concentrations, and leaf and root N content than biocontainers at some harvests. However, biocontainers resulted in greater PGI, dry weights, and N content (in leaves, stems, roots, and total plant) than plastic containers later in the season, from September to December. These differences appeared in September after plants grown in plastic containers ceased active growth in dry weight and N uptake by the end of August. Plants grown in biocontainers had extended active growth from 13 Sept. to 9 Nov., resulting in greater tissue N content and greater N uptake efficiency. The biocontainers used in this study produced azalea plants of greater size, dry weight, and improved N uptake by increasing growth rate and extending the plants’ active growth period into late fall. The beneficial effects likely resulted from greater evaporative cooling through container sidewalls and the lighter color of the biocontainers, and therefore led to lower substrate temperatures and improved drainage.

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Richard L. Harkess and Robert E. Lyons

Histological and histochemical examination of floral initiation was conducted to determine the pattern of flowering in Rudbeckia hirta, a long-day (LD) plant. Plants were grown under 8-hour short days (SDs) until they had 14 to 16 expanded leaves. Half of the group of plants was moved to LD conditions consisting of natural daylength plus a 4-hour night interruption. Rudbeckia hirta had a pattern of differentiation in flowering similar to that reported in species requiring one inductive day for initiation. Rudbeckia hirta required 8 LDs for evocation and 18 LDs for completion of initiation. Involucral bracts initiated after 18 LDs, after which the receptacle enlarged and was capped by a meristematic mantle of cells signaling the start of development. Floret primordia did not initiate, even after 20 LDs. Increases in pyronin staining were observed in actively dividing cells of the procambium, leaf primordium, and corpus of the vegetative meristems. After 8 LDs, the pith rib meristem stained darkly, a result indicating the arrival of the floral stimulus. An increase in pyronin staining was also observed in the meristematic mantle covering the receptacle after 18 LDs, a result indicating increased RNA levels.

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Pablo R. Hidalgo and Richard L. Harkess

Earthworm castings (vermicompost) were evaluated as a substrate amendment for chrysanthemum [Dendranthema ×grandiflora (Ramat.) Kitam.] `Miramar' production. Vermicompost produced from sheep, cattle, and horse manures were mixed at different ratios with 70 peatmoss: 30 perlite (v/v) to create 12 substrates. The 70 peatmoss: 30 perlite mix at 100% and Sunshine® Mix 1 were used as control substrates. The bulk density, percentage of pore space, and water holding capacity increased as vermicompost content increased while the percentage of air space decreased. At 100% vermicompost, water holding capacity and bulk density were greatest in vermicompost from sheep manure. Plants grown in mixtures of 50% vermicompost from sheep had a greater growth index at harvest, foliar area, number of flowers per pot, and dry weight and fewer days for flower development than plants grown in other substrates. Vermicompost from sheep manure added at 50% by volume was most effective as a substrate amendment for chrysanthemum production.