Container-grown landscape plants in the Mid-Atlantic and Southern states are exposed to wide, rapid fluctuations of temperatures, particularly during winter. Thermocouples were placed at three depths and four orientations in the soil mix of 2-year-old, Foster' hybrid holly (Ilex × attenuata ‘Fosteri’) to monitor temperature profiles of 57 liter (nominal 15 gal) containers. These containers were grown conventionally under three treatments: on a bare ground surface (control), inside plastic-film-covered hoop houses, and in the pot-in-pot (PIP) configuration below the ground surface. Temperatures were monitored during both the coldest and the warmest periods of the year in the Moncks Comer, SC, area. In the coldest period, soil temperatures averaged among depths and orientations were 3.6C (6.5F) warmer in the hoop houses than in the control, and 1.1C (2F) warmer in the PIP system than in the control. Although colder than the hoop houses, the average temperatures of the PIP container dropped below 0C (32F) only in the upper 7.6 cm (3 in). Below freezing averages were observed in the control containers, however, in all positions except the center. In the warmest period, the hoop houses were uncovered, becoming additional data points of the control treatments. The PIP system kept overall average soil temperatures 3.3C (6F) cooler than in control containers. Upon conclusion of the experiment, new (beyond transplanted root ball) root dry weights were significantly greater for PIP containers than for control containers.

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Author notes

This article is submitted as Technical Contribution No. 4103 from the South Carolina Agricultural Experiment Station, Clemson University, Clemson, SC.

2Professor, Agricultural & Biological Engineering Department, Clemson University, Clemson, SC 29634-0357.

3Graduate Research Associate, Department of Horticulture and Crop Science, Ohio State University, Columbus, OH 43210.