Hot Pots: Container Color Has a Greater Cooling Effect than Micro-Sprinkler Frequency in Nursery Production

Lloyd Nackley (), Dalyn McCauley, James Owen, Jacob Shreckhise and Jeb Fields ()
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Lloyd Nackley: North Willamette Research and Extension Center, Department of Horticulture, Oregon State University, Corvallis, OR 97331, USA
Dalyn McCauley: North Willamette Research and Extension Center, Department of Horticulture, Oregon State University, Corvallis, OR 97331, USA
James Owen: Application Technology Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Wooster, OH 44691, USA
Jacob Shreckhise: U.S. National Arboretum, Floral and Nursery Plants Research Unit, Agricultural Research Service, Otis L. Floyd Nursery Research Center, U.S. Department of Agriculture, McMinnville, TN 37110, USA
Jeb Fields: Environmental Horticulture Department, University of Florida, Gainesville, FL 32611, USA

Agriculture, 2025, vol. 15, issue 21, 1-15

Abstract: Container production systems are critical for the horticulture industry but are particularly vulnerable to temperature extremes. This study investigated the effects of pot color (black vs. white) and irrigation frequency (single vs. cyclic) on root zone temperature and the growth of Hydrangea paniculata ‘Limelight’, one of the most popular and widely grown container-grown perennial shrubs in North America. The experiment was conducted at the North Willamette Research and Extension Center in Aurora, Oregon, USA (45°16′51″ N, 122°45′04″ W). A total of 160 Hydrangea paniculata ‘Limelight’ plants were divided into two groups of 80 and potted in black or white 11.4 L nursery containers filled with a bark-based potting mix. Pots were randomly assigned to one of two irrigation treatments based on irrigation frequency: single or cyclic. In the single irrigation treatment, pots received one irrigation event at 07:00 h. In the cyclic irrigation treatment, the same total irrigation volume was divided into three equal applications delivered at 08:00, 12:00, and 16:00 h. Results showed that black pots reached significantly higher root zone temperatures than white pots. Cyclic irrigation effectively reduced the peak root zone temperatures in black pots, cooling by as much as 6 °C during hot afternoons compared with single irrigation. Plants in black pots experienced 6×–7× more hours above critical root-zone temperature thresholds (>38 °C) compared with those in white pots. Although the literature indicates that prolonged exposure above 35–38 °C can inhibit photosynthesis and slow growth, and that root growth may cease at ~38 °C, in our study, plant growth was not significantly affected by pot color, irrigation regime, or their interaction (all p > 0.05). This study emphasizes the importance of optimizing pot color and irrigation practices to address vulnerabilities to extreme temperatures in container production systems.

Keywords: climate change; heatwave; heat stress; nursery; Pacific Northwest; RZT; substrate (search for similar items in EconPapers)
JEL-codes: Q1 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 (search for similar items in EconPapers)
Date: 2025
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