Heat stress is problematic to root growth in the production of containerized nursery plants. Container color may moderate effects of solar radiation on substrate temperatures. Studies were conducted near Manhattan, KS, to evaluate effects of container color on growth of roots and shoots in bush beans ( Phaseolus vulgaris L.), red maple ( Acer rubrum L.), and eastern redbud ( Cercis canadensis L.). Four treatments among studies included containers colored flat and gloss white, silver, and black; a green container color treatment was added to the tree studies. Plants were grown in bark-based soil-less substrate and temperatures were measured at 5-cm depths in the south sides and centers. After 4 months, plant variables were measured. Roots were separated into three sections: core, north, and south. In the bean study, substrate temperatures at the south side of the container averaged lowest in flat and gloss white (≈36 °C) and greatest in black containers (50.3 °C). Root density at the south side was reduced in beans by 63% to 71% in black compared with flat and gloss white. In heat-sensitive maples, substrate temperatures at the south side of containers averaged up to 7.7 °C greater in black and green than in other treatments. Substrate temperatures in the center averaged 3.5 to 3.8 °C greater in black than in flat and gloss white, resulting in up to 2.5 times greater root density in flat and gloss white than in black containers. In heat-tolerant redbuds, the effects of container color on whole-plant growth were less evident. Data suggest that heat-sensitive plants benefit from being grown in white containers or painting outer surfaces of green and black containers white.

The objective of this study was to evaluate the potential for use of container substrates composed of processed whole pine trees ( WholeTree ). Three species [loblolly pine ( Pinus taeda ), slash pine ( Pinus elliottii ), and longleaf pine ( Pinus palustris )] of 8- to 10-year-old pine trees were harvested at ground level and the entire tree was chipped with a tree chipper. Chips from each tree species were processed with a hammer mill to pass through a 0.374-inch screen. On 29 June 2005 1-gal containers were filled with substrates, placed into full sun under overhead irrigation, and planted with a single liner (63.4 cm ³ ) of ‘Little Blanche’ annual vinca ( Catharanthus roseus ). The test was repeated on 27 Aug. 2005 with ‘Raspberry Red Cooler’ annual vinca. Pine bark substrate had about 50% less air space and 32% greater water holding capacity than the other substrates. At 54 days after potting (DAP), shoot dry weights were 15% greater for plants grown in 100% pine bark substrate compared with plants grown in the three WholeTree substrates. However, there were no differences in plant growth indices for any substrate at 54 DAP. Plant tissue macronutrient content was similar among all substrates. Tissue micronutrient content was similar and within sufficiency ranges with the exception of manganese. Manganese was highest for substrates made from slash pine and loblolly pine. Root growth was similar among all treatments. Results from the second study were similar. Based on these results, WholeTree substrates derived from loblolly pine, slash pine, or longleaf pine have potential as an alternative, sustainable source for producing short-term horticultural crops.

Native plant use in United States (U.S.) ornamental landscapes is expected to increase in upcoming years. Various market, production, and economic factors may influence a nursery firm’s likelihood of growing and selling native plants. The objective of this study was to investigate production-related factors (e.g., integrated pest management (IPM) strategies, firm characteristics, and plant types sold) that impact commercial native plant sales in the U.S. The research questions included the following: (a) What production factors drive growers to produce native plants? (b) What production factors increase native plant sales? Insights on production-related factors that influence native plant production can be used to understand the decision-making process of native plant growers and encourage additional production of native plants to meet expected increases in demand. Data from the 2014 and 2019 Green Industry Research Consortium’s National Green Industry Survey were used to address this research objective. Green industry firms were categorized by their annual native plant sales, and an ordered probit model was used to assess differences in IPM strategies, firm characteristics, number of plant types grown, sales attributed to different plant types, and actions to address labor issues. In general, firms selling native plants participated in more IPM strategies, sold a more diverse array of plants, and used more sales avenues than non-native plant firms. IPM strategies varied by native plant sales, with firms generating higher native plant sales exhibiting a higher likelihood of removing infested plants, circulating air, managing irrigation, using beneficial insects, and planting pest resistant varieties as part of their IPM strategy than non-native plant firms. Annual native sales and paying higher wages were impacted by plant types sold. Understanding current production and business practices can help identify practices resulting in market success for native plants, the use of which can enhance sustainable landscapes by increasing biodiversity and ecosystem services.

Rising costs of potting substrates have caused horticultural growers to search for alternative, lower-cost materials. Objectives of this study were to determine the extent of nitrogen immobilization and microbial respiration in a high wood-fiber content substrate, clean chip residual. Microbial activity and nitrogen availability of two screen sizes (0.95 cm and 0.48 cm) of clean chip residual were compared to control treatments of pine bark and peatmoss in a 60-day incubation experiment. Four rates (0, 1, 2, or 3 mg) of supplemental nitrogen were assessed. Peatmoss displayed little microbial respiration over the course of the study, regardless of nitrogen rate; followed by pine bark, 0.95 cm clean chip residual, and 0.48 cm clean chip residual. Respiration increased with increasing nitrogen. Total inorganic nitrogen (plant available nitrogen) was greatest with peatmoss; inorganic nitrogen in other treatments were similar at the 0, 1, and 2 mg supplemental nitrogen rates, while an increase occurred with the highest rate (3 mg). Clean chip residual and pine bark were similar in available nitrogen compared to peatmoss. This study suggests that nitrogen immobilization in substrates composed of clean chip residual is similar to pine bark and can be treated with similar fertilizer amendments during nursery production.

A study was conducted at Auburn University in Auburn, AL, and the U.S. Department of Agriculture–Agricultural Research Service, Southern Horticultural Laboratory in Poplarville, MS, to evaluate clean chip residual (CCR) as an alternative substrate component for annual bedding plant production. Clean chip residual used in this study was processed through a horizontal grinder with 4-inch screens at the site and was then processed again through a swinging hammer mill to pass a 3/4- or 1/2-inch screen. Two CCR particle sizes were used alone or blended with 10% (9:1) or 20% (4:1) peatmoss (PM) (by volume) and were compared with control treatments, pine bark (PB), and PB blends (10% and 20% PM). Three annual species, ‘Blue Hawaii’ ageratum ( Ageratum houstonianum ), ‘Vista Purple’ salvia ( Salvia × superba ), and ‘Coral’ or ‘White’ impatiens ( Impatiens walleriana ), were transplanted from 36-cell (12.0-inch ³ ) flats into 1-gal containers, placed on elevated benches in a greenhouse, and hand watered as needed. Ageratum plants grown at Auburn had leaf chlorophyll content similar or greater than that of plants grown in PB. There were no differences in salvia; however, impatiens plants grown in PB substrates at Auburn had less leaf chlorophyll content than those grown in CCR. There were no differences in ageratum, salvia, or impatiens leaf chlorophyll content at Poplarville. There were no differences in growth indices (GI) or shoot dry weight (SDW) of ageratum, while the largest salvia was in PB:PM and the largest impatiens were in PB-based substrates at Auburn. The GI of ageratum at Poplarville was similar among treatments, but plants grown in 4:1 1/2-inch CCR:PM were the largest. Salvia was largest in 4:1 CCR:PM and PB:PM, and although there were no differences in GI for impatiens at Poplarville, the greatest SDW occurred with PB:PM. Foliar nutrient content analysis indicated elevated levels of manganese and zinc in treatments containing CCR at Auburn and PB at Poplarville. At the study termination, two of three annual species tested at both locations had very similar growth when compared with standard PB substrates. This study demonstrates that CCR is a viable alternative substrate in greenhouse production of ageratum, salvia, and impatiens in large containers.