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Stephanie Burnett and Donglin Zhang

In the past, horticulture students at the University of Maine have been taught to irrigate plants using only hand irrigation. It is becoming increasingly important to irrigate and fertilize efficiently in commercial greenhouses in order to reduce water waste and nutrient leaching. In 2004 and 2006, greenhouse management or plant production students were exposed to alternate methods of irrigating Dendranthema ×morifolium (chrysanthemum) in greenhouses to train students more effectively in irrigation techniques. In 2004, students measured the quantity of water applied to chrysanthemums once they reached the permanent wilting point from 26 Sept. until 30 Oct. The irrigation frequency generally increased as crops grew, but, the quantity of water applied upon irrigation was not significantly different. This experience provided students with a tangible idea of how irrigation frequency and timing change as crops grow, which could be applied to irrigation timing decisions in the future. In 2006, students grew a crop of chrysanthemums using alternate methods of irrigation (hand watering vs. drip irrigation) and fertilization. Student surveys in 2006 indicated that only 25% of students with previous experience working in a greenhouse or nursery had grown crops using drip irrigation, but all students with prior experience had irrigated by hand. Expanding student experiences with irrigation in the greenhouse uses active learning to instill students with more knowledge of irrigation and provide them with practical skills for irrigating efficiently and conservatively in the future.

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Shuyang Zhen and Stephanie E. Burnett

There is currently little information regarding the impact of soil moisture on morphology and physiology of English lavender (Lavandula angustifolia). Therefore, our goal was to determine the impact of substrate volumetric water content (θ = volume of water ÷ volume of substrate) on this plant. We grew ‘Munstead’ and ‘Hidcote’ lavender at one of four θ: 0.1, 0.2, 0.3, or 0.4 L·L−1 for 54 days using a capacitance sensor-automated irrigation system. Plant height, greatest width, inflorescence number, and total leaf number and area of both cultivars increased with increasing θ. Shoot fresh and dry weight of lavender irrigated at θ 0.3 L·L−1 was generally twice that of those grown at the lowest θ (0.1 L·L−1). Leaf-level instantaneous net photosynthetic rate (AN) and transpiration (E) of ‘Munstead’ decreased with decreasing θ. This reduction in AN was likely due to the concurrent reduction in stomatal conductance (g S) at lower θ. Similar reductions in AN, E, and g S of ‘Hidcote’ were observed at lower θ (0.2 and 0.3 L·L−1) 5 weeks after the initiation of the study, but not at the end of the study probably due to acclimation of ‘Hidcote’ to mild drought.

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Stephanie Burnett, Paul Thomas and Marc van Iersel

We previously found that incorporation of PEG-8000 into the growing medium delayed germination and resulted in shorter seedlings. However, in that study, we were unable to determine whether the reduced height was merely the effect of delayed germination or of reduced elongation after germination. To answer this question, we studied whether postgermination drenches with PEG-8000 can reduce seedling height. Annual salvia (Salvia splendens F. Sellow. ex Roem. & Shult. `Bonfire') and French marigold (Tagetes patula L. `Boy Orange') seedlings were treated with drenches of PEG-8000: 0, 15, 20, 30, 42, 50, 62, 72, or 83 g·L–1. At least 20% of seedlings treated with 62 to 83 g·L–1 of PEG-8000 were dead 14 d after treatment. Salvia and marigolds treated with the remaining PEG-8000 concentrations were up to 34% and 14% shorter than untreated seedlings, respectively. Leaf water (Ψw) and turgor potential (Ψp) also decreased for salvia which were grown with greater concentrations of PEG-8000, one probable cause of the observed reduction in elongation. Since the PEG-8000 in this study was applied after germination, it is clear that PEG-8000 does not reduce elongation merely by delaying germination, but also by reducing the elongation rate. Thus, postgermination drenches with PEG-8000 can be used to produce shorter seedlings.

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Stephanie Burnett, Marc van Iersel and Paul Thomas

Osmotic compounds, such as polyethylene glycol 8000 (PEG-8000), reduce plant elongation by imposing controlled drought. However, the effects of PEG-8000 on nutrient uptake are unknown. Impatiens `Dazzler Pink' (Impatiens walleriana Hook. F.) were grown hydroponically in modified Hoagland solutions containing 0, 10, 17.5, 25, 32.5, 40, 47.5, 55, or 62.5 g·L–1 PEG-8000. Impatiens were up to 68% shorter than control plants when grown with PEG-8000 in the nutrient solution. Plants treated with PEG-8000 rates above 25 g·L–1 were either damaged or similar in size to seedlings treated with 25 g·L–1 of PEG-8000. Impatiens leaf water potentials (Ψw) were positively correlated with plant height. PEG-8000 reduced the electrical conductivity of Hoagland solutions as much as 40% compared to nontreated Hoagland solutions, suggesting that PEG-8000 may bind some of the nutrient ions in solution. Foliar tissue of PEG-treated impatiens contained significantly less nitrogen, calcium, zinc, and copper, but significantly more phosphorus and nickel than tissue from nontreated impatiens. However, no nutrient deficiency symptoms were induced.

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Jonathan Foster, Stephanie Burnett and Lois Stack

Twinflower (Linnaea borealis) is an understory subshrub native to northern regions of North America, Europe, and Asia. Some growers report that this native plant is difficult to propagate. Although twinflower prefers partial shade and grows in areas with naturally variable moisture, there has been no greenhouse propagation work testing the impact of light or soil moisture conditions on root development of this plant or whether fertilizer impacts root development or root:shoot ratios during propagation. The goal of the first experiment was to propagate twinflower under a variety of daily light integrals (DLI)—27.6, 14.4, or 5.8 mol·m−2·d−1—and soil volumetric water content values (θ = volume of water ÷ volume of soil) 0.30, 0.35, 0.40, and 0.45 L·L−1, both parameters aimed at reproducing a range of natural conditions. The largest roots were grown at DLIs of 5.8 and 14.4 mol·m−2·d−1 and θ values of 0.30 and 0.35 L·L−1. In the second experiment, twinflower plants were grown in substrates with 0, 2.1, or 5.0 g·L−1 of incorporated controlled-release fertilizer (14N–6.1P–11.6K). Root and shoot dry weight increased at both treatment rates. The relative percentages of nitrogen, phosphorus, and potassium, and the total concentrations of manganese in parts per million, increased in foliage, as well. In both experiments, the source of cuttings impacted results. In the first experiment, cuttings taken from the source that was in the most light were least likely to survive (26% survival rate) compared with cuttings taken from stock plants growing in partial shade (65% or 82% survival rates, by site). In the second experiment, cuttings taken from source plants that were most intensively managed for removal of weeds and competing plants had the highest survival rate and the greatest shoot and root dry weight. We recommend propagating twinflower with moderate rates of fertility (i.e., 2.1 g·L−1 of incorporated controlled-release fertilizer) under some shade (5.8–14.4 DLI) and a moderate θ (0.30–0.35 L·L−1).

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Stephanie E. Burnett and Lois Berg Stack

Organic and conventional greenhouse growers in Maine were surveyed to determine the research needs of growers who may produce organic ornamental bedding plants. Organic growers were also asked to identify their greatest motivator to determine whether they feel that there is a greater market for organically grown ornamental plants. The greatest percentage (75%) of organic growers indicated that they choose to grow plants organically because “it's the right thing to do.” The second greatest percentage (36%) of organic growers choose organic production techniques for ornamental plants because they grow food crops organically and consider it convenient to use only one production technique. A relatively small number of organic growers (7%) considered the market for organic ornamental plants to be a strong motivator for growing organically. Organic growers were asked to select production issues that pose the greatest challenge for them from a list of common production problems. They considered insect and disease management and organic fertility, substrate, and pH management to be their greatest problems. Conventional growers primarily avoid organic production techniques because they consider organic fertilization or organic insect management to be too big of a challenge. Because organic and conventional growers consider insect and fertility or substrate management to be challenges facing organic growers, these topics should be top priorities for future research on organic greenhouse production.

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Stephanie E. Burnett and Marc W. van Iersel

Gaura lindheimeri Engelm. & Gray ‘Siskiyou Pink’ (gaura) and Phlox paniculata L. ‘David’ (garden phlox) were grown for 5 weeks in substrates irrigated at volumetric water contents (Θ) of 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, or 0.45 m3·m−3 using a capacitance sensor-controlled irrigation system. Volumetric water contents of the substrate measured by the capacitance sensors controlling irrigation were correlated with measurements with a separate handheld meter (r 2 = 0.83) and with volumetric water content set points throughout the study (r 2 > 0.98). Only 3.8 (at an irrigation set point of 0.10 m3·m−3) to 53 L (0.45 m3·m−3) of water was used to irrigate gaura and phlox and 0 to 7.74 L of this water leached out of the substrates. Significant leaching occurred only at Θ set points of 0.40, or 0.45 m3·m−3. Gaura had shorter and fewer branches and reduced dry weight when grown at lower volumetric water contents, but plants irrigated at set points above 0.25 m3·m−3 were large enough to be marketable. Gaura may be grown with capacitance sensor-automated irrigation using water efficiently and minimizing or eliminating leachate and thus nonpoint source pollution.

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Ajay Nair, Donglin Zhang and Stephanie Burnett

Euphorbia pulcherima Willd. ex Klotzsch (poinsettia) are grown commercially in all 50 states. This experiment was conducted to find a suitable media for cultivating `White Star' poinsettia under natural day-length conditions in Orono, Maine. The growth, morphology, and foliar and substrate nutrient concentration of `White Star' poinsettia was evaluated in three different media formulations (Promix®, Metromix-560®, and a 1:1 v/v mixture of Promix® and Metromix-560®). Results indicated minimal variability in overall plant height, but there were significant differences in the canopy area. Canopy area was greatest for plants grown in Promix® followed by a combination of Promix® and Metromix-560®. Plants grown in Promix® recorded the highest fresh weight (170.6 g). Bract area was statistically insignificant among the three treatments. Nutrient status of the media varied widely and was significant for nitrate–nitrogen, phosphorus, soluble salts, iron, calcium, magnesium, manganese, sodium, sulfur, and zinc. Foliar analysis revealed that nutrient concentrations also significantly differed across treatment media. Optimum media pH for growing poinsettia ranges from 6.0 to 7.5. Media pH for Promix® was 5.9, which was significantly higher than Metromix-560® (4.65) and Promix® + Metromix-560® (1:1 v/v; 5.3). In spite of significant differences in foliar and substrate nutrient concentrations, overall plant growth remained the same.

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Bryan J. Peterson, Stephanie E. Burnett and Olivia Sanchez

Although overhead mist revolutionized the propagation industry, it does suffer from potential drawbacks that include the application of large volumes of water, potentially unsanitary conditions, irregular misting coverage, and leaching of foliar nutrients. We explored the feasibility of submist as an alternative as it might avoid these problems by applying water exclusively from below the cutting, which is inserted basally into an enclosed rooting chamber. We propagated cuttings of korean lilac (Syringa pubescens ssp. patula) and inkberry (Ilex glabra) using both overhead mist and submist to compare effectiveness of the systems. Cuttings of korean lilac were wounded and dipped basally into 8000 mg·L−1 of the potassium salt of indole-3-butyric acid (K-IBA), and those in the overhead mist systems were inserted into coarse perlite. Cuttings of inkberry were wounded and treated with 5000 mg·L−1 K-IBA, and those in the overhead mist systems were inserted into 50:50 peat:perlite (by vol). Cuttings of korean lilac in the submist systems produced more than twice as many roots as cuttings in the overhead mist systems, with roots more than 2.6 times the length. Similarly, cuttings of inkberry in the submist systems produced more than three times the root counts and root lengths as cuttings in the overhead mist systems. For korean lilac, root dry weights averaged 58 mg for cuttings in the submist system, compared with only 18 mg among cuttings receiving overhead mist. Likewise, root dry weights averaged 70 and 7 mg for cuttings of inkberry propagated by submist and overhead mist, respectively. Rooted cuttings of korean lilac transplanted well into a soilless substrate, where they more than tripled their root biomass to 218 mg (vs. 59 mg for cuttings transplanted from overhead mist). We did not evaluate transplant performance of inkberry. Our results show that submist systems might merit consideration for the propagation of woody plants by leafy stem cuttings.

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Stephanie E. Burnett, Marc W. van Iersel and Paul A. Thomas

French marigold (Tagetes patula L. `Boy Orange') was grown in a peat-based growing medium containing different rates (0, 15, 20, 30, 42, or 50 g·L–1) of polyethylene glycol 8000 (PEG-8000) to determine if PEG-8000 would reduce seedling height. Only 28% to 55% of seedlings treated with 62, 72, or 83 g·L–1 of PEG-8000 survived, and these treatments would be commercially unacceptable. Marigolds treated with the remaining concentrations of PEG-8000 had shorter hypocotyls, and were up to 38% shorter than nontreated controls at harvest. Marigold cotyledon water (ψw), osmotic (ψs), and turgor (ψp) potentials were significantly reduced by PEG-8000, and ψp was close to zero for all PEG-treated seedlings 18 days after seeding. Whole-plant net photosynthesis, whole-plant dark respiration, and net photosynthesis/leaf area ratios were reduced by PEG-8000, while specific respiration of seedlings treated with PEG-8000 increased. Marigolds treated with concentrations greater than 30 g·L–1 of PEG-8000 had net photosynthesis rates that were close to zero. Fourteen days after transplanting, PEG-treated marigolds were still shorter than nontreated seedlings and they flowered up to 5 days later. Concentrations of PEG from 15 to 30 g·L–1 reduced elongation of marigold seedlings without negatively affecting germination, survival, or plant quality. It appears that marigold seedlings were shorter because of reduced leaf ψp and reductions in net photosynthesis.