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Alyssa J. Brown, Phil S. Allen, Greg V. Jolley, and J. Ryan Stewart

For the past several years, many college horticulture programs have experienced a decline in undergraduate enrollment, resulting in the elimination of some degrees. In this study, we compared postsecondary U.S. horticulture program availability from a survey completed in 1997 with offerings existing in 2012 and 2017. In 1997, 446 U.S. postsecondary institutions offered degrees and/or certificates in horticulture. In 2012, this number had decreased by 43% to 253 institutions, which included 98 with 4-year degrees, 215 with 2-year degrees, and 138 with certificate programs. In 2017, the total number of institutions offering horticulture-related degrees and/or certificates decreased to 209, representing a 53% decrease over the 20 years from 1997 to 2017 and a 17% decrease during the 5-year period between 2012 and 2017. In 2017, 85 institutions offered 4-year degrees, 133 offered 2-year degrees, and 98 offered certificate programs, which over this 5-year period represents decreases of 13%, 38%, and 29%, respectively. “Horticulture” was the most common program title in both 2012 and 2017, and the percentage of programs with this name increased during the 5-year period for all program types. In 2017, 28 horticulture programs not identified in the 1997 survey were found, but only two of these were confirmed to have been created since 1997. Overall, these data suggest a trajectory toward elimination of 2-year and certificate programs, and continued consolidation for 4-year degrees. If it continues, this trend is not favorable for the continued vitality of postsecondary horticulture programs in the United States and may impact progress negatively for the field of horticulture as a whole.

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Andrew K. Koeser, Sarah T. Lovell, Aaron C. Petri, Robin G. Brumfield, and J. Ryan Stewart

This study assessed the material and energy inputs required to produce a Petunia ×hybrida plant from initial propagation to delivery at a regional distribution center. Impacts were expressed in terms of their contribution to the carbon footprint or global warming potential (GWP) of a single finished plant in a ≈10-cm diameter container. Beyond this baseline assessment, the study investigated the secondary impacts (e.g., irrigation demand) associated with container type used. Life cycle assessment data were sourced from interviews, published literature, propriety data sources, direct metering at the greenhouse facility, and original findings from a series of university greenhouse experiments. Results show that a traditional plastic container accounts for ≈16% of overall CO2e emissions (0.544 kg) during petunia production. Although the container was a significant contributor to GWP, electrical consumption for supplemental lighting and irrigation during plug production proved to be the leading source of CO2e emissions (over 47%) in our model system. Differences in GWP when considering secondary impacts associated with the various biocontainers were minor, especially when compared with the other elements of production. Our results demonstrate that biocontainers could potentially be as or more sustainable than plastic pots once pot manufacturing and end-of-life data are considered. However, use of more efficient supplemental lighting sources may ultimately have the greatest impact on overall GWP for the production system assessed.

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J. Ryan Stewart, Roger Kjelgren, Paul G. Johnson, and Michael R. Kuhns

Although transplanted trees typically establish and grow without incident in frequently irrigated turfgrass, their performance in precisely irrigated turfgrass in an arid climate is not known. We investigated the effect of precision irrigation scheduling on growth and water relations of balled-and-burlapped littleleaf linden (Tilia cordata Mill. `Greenspire') planted in buffalograss (Buchloë dactyloides [Nutt.] Engelm. `Tatanka') and kentucky bluegrass (Poa pratensis L.). Over 2 years, trees in turfgrass were irrigated either by frequent replacement based on local reference evapotranspiration, or precision irrigated by estimating depletion of soil water to the point of incipient water stress for each turfgrass species. Predawn leaf water potential and stomatal conductance of trees were measured during first-year establishment, and predawn leaf water potential was measured during a mid-season water-deficit period during the second year. Trunk diameter growth and total tree leaf area were measured at the end of each year. Values of predawn leaf water potential and stomatal conductance of trees in precision-irrigated buffalograss were lower (–0.65 MPa, 25.3 mmol·m–2·s–1) than those of trees in the other treatments near the end of the first growing season. The longer interval between precision irrigations resulted in mild water stress, but was not manifested in growth differences among trees across treatments during the first season. During the water-deficit period of the second year, there was no evidence of stress among the trees regardless of treatment. At the end of the second season, total leaf area of trees grown in precision-irrigated kentucky bluegrass (1.10 ± 0.34 m2) was 46% of that of trees grown in buffalograss (2.39 ± 0.82 m2) that were irrigated frequently. Trunk diameter growth of trees in frequently irrigated kentucky bluegrass (1.91 ± 2.65 mm) was 29% of that of the trees grown in buffalograss (6.68 ± 1.68 mm), regardless of irrigation treatment, suggesting a competition effect from kentucky bluegrass. We conclude that frequent irrigation of balled-and-burlapped trees in turfgrass, particularly buffalograss, is more conducive to tree health during establishment than is maximizing the interval between turfgrass irrigation. Regardless of irrigation schedule, kentucky bluegrass appears to impact tree growth severely during establishment in an arid climate.

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Andrew K. Koeser, J. Ryan Stewart, Germán A. Bollero, Donald G. Bullock, and Daniel K. Struve

Transplanted trees are exposed to numerous stresses from the time of harvest until establishment in the landscape. Although an individual stress factor may be the sole cause of plant death or decline, it is more likely a combination of stress factors cause reduced growth or death after planting. In an effort to isolate the stresses associated with three critical stages in the transplanting process (i.e., initial harvest, handling, and transport), 5-cm-caliper, balled-and-burlapped Acer rubrum L. ‘Red Sunset’ (red maple) and Acer platanoides L. ‘Pond’ (Norway maple) trees at three sites (Urbana, IL; Union, IL; and Manitowoc, WI) were subjected to three treatments: root-pruned, handled, and transported. Effects of water stress, root severance, and root-ball disruption on twig elongation and tree survival were measured for each treatment and compared with unaltered control trees. Twig elongation was greater in unaltered control trees when compared with root-pruned trees. In addition, root-pruned trees exhibited greater twig elongation when compared with either handled or transported trees suggesting that although initial root severance did affect growth, it was not as detrimental as lifting and handling. In addition, twig elongation was not different between handled and transported trees. Water potential measurements ranged from –0.2 to –2.0 MPa, suggesting water stress was not a critical factor during the time of transplanting. Similarly, root-ball soil moisture varied little between treatments over the course of transplanting. Results suggest rough handling before and after transport should be minimized in an effort to maximize growth and transplant success.

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J. Ryan Stewart, Reid D. Landes, Andrew K. Koeser, and Andrea L. Pettay

Frequent episodes of water stress in managed landscapes have led the nursery industry to look for attractive woody species that perform well under extreme conditions of drought and flooding. We chose to evaluate three taxa with highly localized natural distributions in the United States, Calycanthus occidentalis (north–central California), Fraxinus anomala (northeastern Utah), and Pinckneya pubens (northeastern Florida), each of which may merit further use under cultivated conditions beyond their respective ranges. Although widespread cultivation of each taxon may not be possible as a result of limitations related to cold hardiness, we hypothesized that each species can tolerate extremes in soil moisture availability more so than their native habitats imply. Our objective was to characterize, under greenhouse conditions, how the quantity of soil water affects gas exchange of potted plants of each species. Plants were divided into five groups, each exposed to treatment conditions ranging from complete submersion to severe drought. Complete submersion killed plants of C. occidentalis and F. anomala, although in drought or severe drought conditions, C. occidentalis plants had lower net photosynthesis and less leaf area and plant dry weight than control plants. Net photosynthesis, leaf area, and plant dry weight of partially flooded plants, however, were not found to be significantly less than that of the control plants. Mean net photosynthetic levels and plant dry weights of severe drought, drought, and control F. anomala did not differ. While severe drought plants of P. pubens exhibited much lower levels of net photosynthesis, but not plant dry weights or leaf area, than the control plants, those exposed to drought, partial flood, and complete submersion were not found to differ in net photosynthesis levels from the control plants. Due to the sustained tolerance of F. anomala and P. pubens to a range of extreme soil moisture conditions, as exhibited by net photosynthetic responses, carbon accumulation, and survival, we conclude that use of these species in landscapes is warranted if invasiveness and other potential problems are not identified. Calycanthus occidentalis, however, appears unsuitable for cultivation in areas with organic soils greater than ≈66% and lower than ≈30% soil moisture content as a result of its high mortality in flooded conditions and poor physiological responses under dry conditions.

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Renee Conneway, Sven Verlinden, Andrew K. Koeser, Michael Evans, Rebecca Schnelle, Victoria Anderson, and J. Ryan Stewart

While research on the use of alternative containers for greenhouse production is growing, most studies have focused on a limited number of types of alternative containers and primarily on short-term greenhouse crops. With the recent release of several new bioplastic alternatives, comparisons to established alternative containers and production of longer rotation ornamental crops should be investigated. Our work, therefore, investigates the performance of ten commercially available alternative containers and their effects on both a short-term ‘Sunpatiens Compacta’ impatiens (Impatiens ×hybrida) and a long-term greenhouse crop ‘Elegans Ice’ lavender (Lavendula angustifolia) at four different locations. Results indicated that plant growth in terms of dry weight differed by container at most locations. Combined analysis of all locations showed that only straw and a bioplastic sleeve outperformed plastic pots in terms of shoot dry weight and then only after 12 weeks of production. Leachate pH, but not electrical conductivity (EC), varied by container in both the short- and long-term crop with alternative containers made from composted cow manure and peat showing consistently higher and lower pH readings, respectively. Postharvest container strength varied significantly by container, with the plastic control maintaining the highest puncture resistance after both 6 and 12 weeks, in some instances matched by the puncture strength of coconut fiber pots. Some alternative containers, in particular, wood, manure, and peat showed algal growth after 6 and 12 weeks of greenhouse production. We conclude that while some alternative containers were linked to increased growth, most showed growth equal to the plastic control, and could therefore make appropriate alternatives to plastic pots. However, changes in pH, low puncture strengths after production, higher denesting times, and algal growth on manure, wood, and peat may make these pots less desirable alternatives than other pots under investigation. However, other factors not studied here, such as compostability, biodegradability in the landscape, water use, consumer preference, aesthetics, compatibility with mechanized operations, and cost may also need to be taken into account when deciding on an appropriate container for greenhouse production.

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Michael R. Evans, Andrew K. Koeser, Guihong Bi, Susmitha Nambuthiri, Robert Geneve, Sarah Taylor Lovell, and J. Ryan Stewart

Nine commercially available biocontainers and a plastic control were evaluated at Fayetteville, AR, and Crystal Springs, MS, to determine the irrigation interval and total water required to grow a crop of ‘Cooler Grape’ vinca (Catharanthus roseus) with or without the use of plastic shuttle trays. Additionally, the rate at which water passed through the container wall of each container was assessed with or without the use of a shuttle tray. Slotted rice hull, coconut fiber, peat, wood fiber, dairy manure, and straw containers were constructed with water-permeable materials or had openings in the container sidewall. Such properties increased the rate of water loss compared with more impermeable bioplastic, solid rice hull, and plastic containers. This higher rate of water loss resulted in most of the biocontainers having a shorter irrigation interval and a higher water requirement than traditional plastic containers. Placing permeable biocontainers in plastic shuttle trays reduced water loss through the container walls. However, irrigation demand for these containers was still generally higher than that of the plastic control containers.

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Robin G. Brumfield, Laura B. Kenny, Alyssa J. DeVincentis, Andrew K. Koeser, Sven Verlinden, A.J. Both, Guihong Bi, Sarah T. Lovell, and J. Ryan Stewart

Greenhouse growers find themselves under increasing pressure to respond to consumer preferences to use environmentally sustainable practices and materials while maintaining profitable operations. These consumer preferences reflect a mounting awareness of the environmental issues, such as climate change and their associated social costs. Ideally, sustainable horticultural production accounts for both traditional economic considerations and such social costs, some of which can be explained through the calculation of global warming potential (GWP). An obvious candidate for a sustainable intervention is the traditional plastic pot, which growers can replace with alternative biocontainers with varying degrees of GWP. This study calculates the variability of direct costs of production using alternative containers to offer a comparison of social and economic costs. We evaluated these direct costs of producing petunia (Petunia ×hybrida) grown in pots made of traditional plastic, bioplastic, coir, manure, peat, bioplastic sleeve, slotted rice hull, solid rice hull, straw, wood fiber, and recycled reground plastic containers used in a previous assessment of GWP. Our analysis of the costs when using a traditional plastic pot showed that the highest contributors to GWP were different from the highest contributors to direct costs, revealing that the price does not reflect the environmental impact of several inputs. Electricity, the plastic shuttle tray, and the plastic pot contributed most to GWP, whereas labor, the plastic container, and paclobutrozol growth regulator contributed most to direct cost of production (COP). At 64% of total cost, labor was the most expensive input. Watering by hand added another $0.37–$0.54 per plant in labor. When we analyzed input costs of each alternative container separately, container type had the largest impact on total direct costs. Before adding container costs, the direct COP ranged from $0.56 to $0.61 per plant. After adding containers, costs ranged from $0.61 to $0.97 per plant. Wood fiber pots were the most expensive and recycled reground plastic pots were the least expensive in this study. Based on our assessment and the observed small variation in GWP between alternative containers, growers would benefit from selecting a container based on price and consumer demand. Some social costs that we are not aware of yet may be associated with some or all biocontainers.

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Robin G. Brumfield, Alyssa J. DeVincentis, Xueni Wang, R. Thomas Fernandez, Susmitha Nambuthiri, Robert L. Geneve, Andrew K. Koeser, Guihong Bi, Tongyin Li, Youping Sun, Genhua Niu, Diana Cochran, Amy Fulcher, and J. Ryan Stewart

As high-input systems, plant production facilities for liner and container plants use large quantities of water, fertilizers, chemical pesticides, plastics, and labor. The use of renewable and biodegradable inputs for growing aesthetically pleasing and healthy plants could potentially improve the economic, environmental, and social sustainability of current production systems. However, costs for production components to integrate sustainable practices into established systems have not been fully explored to date. Our objectives were to determine the economic costs of commercial production systems using alternative containers in aboveground nursery systems. We determined the cost of production (COP) budgets for two woody plant species grown in several locations across the United States. Plants were grown in plastic pots and various alternative pots made from wood pulp (WP), fabric (FB), keratin (KT), and coconut fiber (coir). Cost of production inputs for aboveground nursery systems included the plant itself (liner), liner shipping costs, pot, pot shipping costs, substrate, substrate shipping costs, municipal water, and labor. Our results show that the main difference in the COP is the price of the pot. Although alternative containers could potentially increase water demands, water is currently an insignificant cost in relation to the entire production process. Use of alternative containers could reduce the carbon, water, and chemical footprints of nurseries and greenhouses; however, the cost of alternative containers must become more competitive with plastic to make them an acceptable routine choice for commercial growers.