Papers by stephanie burnett
HortScience, 2019
The recent increased market demand for locally grown produce is generating interest in the applic... more The recent increased market demand for locally grown produce is generating interest in the application of techniques developed for controlled environment agriculture (CEA) to urban agriculture (UA). Controlled environments have great potential to revolutionize urban food systems, as they offer unique opportunities for year-round production, optimizing resource-use efficiency, and for helping to overcome significant challenges associated with the high costs of production in urban settings. For urban growers to benefit from CEA, results from studies evaluating the application of controlled environments for commercial food production should be considered. This review includes a discussion of current and potential applications of CEA for UA, references discussing appropriate methods for selecting and controlling the physical plant production environment, resource management strategies, considerations to improve economic viability, opportunities to address food safety concerns, and the p...
Acta Horticulturae, 2011
There is wide variety of soil moisture sensors available for use in greenhouse production and res... more There is wide variety of soil moisture sensors available for use in greenhouse production and research applications. Such sensors can play a valuable role in improving uniformity of substrate water content in greenhouses, as well as in automating irrigation based on plant water use. Quantification of spatial variability can be used to improve the design of irrigation systems to better match plant water use. The use of soil moisture sensors for irrigation control is promising, because it can greatly reduce temporal variability in substrate water content by watering based on actual crop water use. This not only results in better temporal uniformity, but can also greatly reduce water use. Understanding the spatial distribution of substrate water content and root water uptake within a container is important in determining the optimal sensor location within a container. At the same time, the properties of different sensors need to be considered when choosing the optimal sensor for a particular application. In small containers, it may be possible to measure most of the substrate with a single sensor, while in larger containers sensors ideally would be placed in that part of the substrate where most of the water uptake occurs.
Scientia Horticulturae, 2016
The value of organic greenhouse production in the United States is $112 million, and organic flor... more The value of organic greenhouse production in the United States is $112 million, and organic floriculture production has increased 40% in greenhouses since 2008. The U.S. National Organic Program (NOP) guidelines allow organic production in containers. One of the primary concerns for current and potential organic container growers is managing container substrate and plant fertility. This manuscript provides a review of current literature on organic substrates and fertilizers for container grown herbs, vegetables and herbaceous ornamentals according to NOP guidelines. Organic-approved substrates can be purchased from commercial suppliers or produced in house. Many organic substrate components are similar to those used in conventional production (peat moss, pine bark, perlite, vermiculite, rice hulls, and whole pine tree) but lack a synthetic wetting agent. Growers who mix their own substrates often add compost at percentages ranging from 20 to 50%. Compost has high water holding and cation exchange capacity. It is often locally or regionally produced and purchased, which impacts variability and quality. For this reason, growers often need to manage substrates with compost more carefully. Single source or blended organic fertilizers may be incorporated in substrates prior to planting. These are derived from a variety of plant and animal based sources. A small number of mined components may be added to substrate-incorporated fertilizers (i.e. limestone). These fertilizers will typically last for four to five weeks, and are often supplemented with liquid fertilizers for longer-term crops or species with high nitrogen requirements. Liquid fertilizers also tend to be more quickly plant available compared to substrate-incorporated fertilizers. With careful management, it is possible to grow container plants in organic production systems that are comparable to those produced in conventional production systems.
Journal of Environmental Horticulture
Submist aeroponic propagation systems apply mist to the bases of cuttings, rather than from overh... more Submist aeroponic propagation systems apply mist to the bases of cuttings, rather than from overhead. These systems improve rooting in some plant species and reduce water usage compared to overhead mist systems. Submist systems, which were supplemented with infrequent overhead mist, were used to propagate stem cuttings collected from six plant species: bluestar (Amsonia tabernaemontana Walter), purple smoke false indigo (Baptisia australis x B. alba ‘Purple Smoke'), threadleaf coreopsis (Coreopsis verticillata L.), panicle hydrangea (Hydrangea paniculata Siebold), sweetgale (Myrica gale L.), and ninebark (Physocarpus opulifolius (L.) Maxim ‘Diablo'). The submist systems were compared to traditional overhead mist with a solid propagation medium. Rooting was better in overhead mist for cuttings of threadleaf coreopsis and purple smoke false indigo. Rooting was comparable between systems for all other species (bluestar, panicle hydrangea, sweetgale, and ninebark). In the submis...
HortTechnology
The novel propagation system submist, which applies water to the bases of cuttings rather than ov... more The novel propagation system submist, which applies water to the bases of cuttings rather than overhead, is a promising alternative. We developed and tested a commercial-scale submist system to make this propagation system more accessible to commercial propagators. Five species, including blue star flower (Amsonia tabernaemontana), faassen nepeta (Nepeta ×faassenii ‘Six Hills Giant’), panicle hydrangea (Hydrangea paniculata ‘Grandiflora’), sweetgale (Myrica gale), and sweetfern (Comptonia peregrina), were propagated from cuttings in commercial-scale submist and overhead mist systems. Blue star flower and faassen nepeta cuttings had greater root length, root rating, and root number with the submist system. Panicle hydrangea cuttings had more roots in submist, but longer roots in overhead mist. There were no differences in rooting between the systems for sweetgale and sweetfern cuttings. The comparable or superior rooting of these five species in a submist system compared with traditi...
HortTechnology
Twinflower (Linnaea borealis) is an understory subshrub native to northern regions of North Ameri... more 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 substrat...
HortScience
We previously found that incorporation of PEG-8000 into the growing medium delayed germination an... more 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-...
HortTechnology
In 2008, we administered a survey to participants at four venues in Maine to determine: 1) the de... more In 2008, we administered a survey to participants at four venues in Maine to determine: 1) the degree of interest in organically, sustainably, and locally grown plants; 2) whether respondents would pay more for these plants compared with conventional plants; and 3) which demographic groups expressed the greatest interest in organically, sustainably, or locally grown plants. Respondents were highly interested in organic and sustainable vegetable/herb and ornamental plants; median interest was 9 on a scale of 1 to 10 where 1 indicated low interest and 10 indicated high interest. They were less interested in locally grown plants; respondents’ median interest in local plants was 6 on the same scale. Survey respondents stated that they would pay 15% more (vegetable/herbs) or 10% more (ornamentals) for organic, sustainable, or local plants than they would for conventionally grown plants. Several demographic factors indicated that respondents were either willing to spend more money on nonc...
HortScience
The growth of three english ivy cultivars in ebb-and-flow subirrigation systems was examined unde... more The growth of three english ivy cultivars in ebb-and-flow subirrigation systems was examined under three photosynthetic photon flux (PPF) treatments (low, medium, or high, corresponding to an average daily PPF of 3.2, 5.4, or 8.5 mol·m–2·d–1, respectively) and four fertilizer concentrations (0, 100, 200, or 300 mg·L–1 N) geared toward production of acclimatized foliage plants. Marketable quality english ivy can be subirrigated with 100 mg·L–1 N. Although 8.5 mol.m–2.d–1 produced the maximum shoot dry weight (SDW), good quality plants also were produced under 5.4 mol·m–2·d–1. `Gold Child', `Gold Dust', and `Gold Heart' english ivy produced with low fertility and low light may be better acclimatized and show superior performance in interior environments. Under light levels lower than 8.5 mol·m–2·d–1, `Gold Heart' had less variegation (12% or 21% for ivy grown under 3.2 or 5.4 mol·m–2·d–1, respectively). `Gold Dust' and `Gold Child' had 65% and 22% variegated le...
HortScience
French marigold (Tagetes patula L. `Boy Orange') was grown in a peat-based growing medium con... more 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 PE...
HortScience
Euphorbia pulcherima Willd. ex Klotzsch (poinsettia) are grown commercially in all 50 states. Thi... more 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...
HortScience
In the past, horticulture students at the University of Maine have been taught to irrigate plants... more 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 ...
HortScience
In commercial greenhouses, fan flower ‘Whirlwind Blue’ (Scaevola aemula R. Br.) plants are sensit... more In commercial greenhouses, fan flower ‘Whirlwind Blue’ (Scaevola aemula R. Br.) plants are sensitive to phosphorus applications in the range typically applied to other floricultural crops. To quantify this response, fan flower plants were grown in Hoagland solutions containing 0, 20, 40, 60, or 80 mg·L−1 P. Plants fertilized with either the highest (80 mg·L−1) or lowest (0 mg·L−1) P concentrations had significantly shorter stems and smaller shoot dry weights and leaf areas than plants fertilized with 20 to 60 mg·L−1 P. Low or high P concentrations negatively impacted flower number; fan flower fertilized with 0, 60, or 80 mg·L−1 P had fewer flowering branches and flowers compared with plants fertilized with 20 to 40 mg·L−1 P. Plants receiving no P had longer roots than those receiving any P and had greater root dry weights than plants receiving all other P concentrations except 20 mg·L−1. Foliar nutrient analysis indicated that although P treatments significantly impacted foliar conc...
HortScience
More efficient irrigation practices are needed in ornamental plant production to reduce the amoun... more More efficient irrigation practices are needed in ornamental plant production to reduce the amount of water used for production as well as runoff of fertilizers and pesticides. The objective of this study was to determine how different substrate volumetric water contents (θ) affected petunia (Petunia ×hybrida) growth and to quantify the daily water use of the plants. A soil moisture sensor-controlled irrigation system was used to maintain θ within ≈0.02 m3·m−3 of the θ threshold values for irrigation, which ranged from 0.05 to 0.40 m3·m−3. Shoot dry weight increased as the θ threshold increased from 0.05 to 0.25 m3·m−3 and was correlated with the total amount of irrigation water applied over the 3-week course of the experiment. The daily water use of the petunias grown with a θ threshold of 0.40 m3·m−3 was 12 to 44 mL/plant and was positively correlated with both plant age and daily light integral. Lower θ thresholds resulted in a decrease in both leaf water (ψ) and osmotic potentia...
HortScience
Gaura lindheimeri Engelm. & Gray ‘Siskiyou Pink’ (gaura) and Phlox paniculata L. ‘David’ (garden ... more 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 enou...
HortScience
Osmotic compounds, such as polyethylene glycol 8000 (PEG-8000), reduce plant elongation by imposi... more 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 cop...
HortScience
Many ornamental plant growers water excessively to reduce the risk of drought stress. Scheduling ... more Many ornamental plant growers water excessively to reduce the risk of drought stress. Scheduling irrigation in greenhouses is challenging because there is little quantitative information about ornamental plant water requirements and how water use changes when plants are grown in varying greenhouse environmental conditions. Models to estimate the daily water use (DWU) of greenhouse crops may provide a useful tool to conserve irrigation water. Our objective was to develop a model to predict DWU based on plant age and easily acquirable environmental data. Two petunia (Petunia ×hybrida) cultivars, Single Dreams Pink and Prostrate Easy Wave Pink, were grown in different sized containers (diameter = 10, 12.5, and 15 cm) to quantify their DWU for 6 weeks. The substrate water content (θ, v/v) was maintained at 0.40 m3·m−3 using an automated irrigation system with capacitance soil moisture sensors. Every irrigation event was recorded by a data logger, and this information was used to calcula...
HortScience
Two experiments were conducted to determine how different substrate volumetric water contents (θ ... more Two experiments were conducted to determine how different substrate volumetric water contents (θ equals volume of water per volume of substrate) affected morphology and physiology of three popular perennials using a capacitance sensor-automated irrigation system. In the first study, rosemary (Rosmarinus officinalis) was grown at one of eight θ set points ranging from 0.05 to 0.40 L·L−1. In the second study, Canadian columbine (Aquilegia canadensis ‘Pink Lanterns’) and cheddar pink (Dianthus gratianopolitanus ‘Bath’s Pink’) were grown at one of nine θ set points ranging from 0.05 to 0.45 L·L−1. Total leaf number and area as well as shoot fresh and dry weight of rosemary plants grown at θ of 0.20 L·L−1 or greater were approximately twice that of those grown at lower θ. Canadian columbine height increased as θ increased. Leaf area of cheddar pink grown at θ of 0.35 L·L−1 or higher was twice that of plants grown at the lowest θ. Shoot dry weight of Canadian columbine was not significant...
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Papers by stephanie burnett