The influence of bed cover type (gravel vs plastic) on container-grown plants

Abstract

Growers report that plants on a gravel bed cover often require more frequent irrigation compared to plants on a plastic bed cover. Three experiments were conducted to determine the cause of this reported observation. The objective of Expt. 1 was to determine if bed cover type (gravel or plastic) influenced the container environment or growth of Rhododendron ‘Girard Pleasant White’ and Ilex crenata Thunb. ‘Bennets Compacta’ in 11.4 L pine bark-filled containers. Measurements included bed cover, substrate, and plant canopy temperatures; evapotranspiration, stem water potential, and plant widths were also determined. The objective of Expt. 2 and 3 was to determine the amount of water retained by the container substrate following irrigation and drainage on gravel or plastic bed covers. Pine bark-filled containers (3.8 L) on gravel or plastic beds were irrigated, allowed to drain for one h, and the amount of water retained in the container substrate was determined. In Expt. 1, bed cover temperatures (0730 to 1930 HR) and container substrate temperatures (2300 to 0400 HR) were about 2 and 1C higher, respectively, for plastic than for gravel. There were no bed cover treatment differences for other measurements. In Expt. 2, containers on plastic beds with a minimal slope retained more water than containers on gravel; water puddled at the base of containers on plastic but not on gravel. When beds were sloped so that a minimal amount of water collected at the base of containers, there was no influence of bed cover type on substrate water retention (Expt. 3). Thus, the influence of bed cover type on substrate water retention following irrigation and drainage was dependent on bed design.