Michael Knee, Daniel K. Struve, Michael H. Bridgewater, and Joseph W. Phillips, Department of Horticulture and Crop Science, The Ohio State University.
The Ohio production system allows trees to be produced from seed or cuttings and grown to marketable size in two to three years (Struve, 1996). After the first year of growth in the greenhouse, the trees are grown in copper-treated containers. In many nurseries, containers are placed on the ground, on a gravel or fabric surface. This exposes them to the sun, which causes the temperature in the root zone to rise as high as 50°C and can lead to inhibition of growth or even death of roots (Struve, unpublished observations).
Some nurseries have adopted the "pot in pot" system of production, whereby each container is set within an outer container that is sunk in the ground (Parkerson, 1990). This protects the pot from heat input at the sides and has the further advantage of natural protection from freezing during the winter.
There have been few direct comparisons of root growth, water use, and overall plant performance for trees in conventional and pot-in-pot systems. The authors set out to determine whether some of the predicted advantages of the pot-in-pot system were realized in practice. We were also interested in comparing the water usage of four Ohio-native tree species in the Fabaceae family, in the context of nursery production and potential for use in dry landscape situations.