I’ve long said that pot color makes a large difference in growing success and here’s the proof you’ve been looking for.
The test plants were bush beans, red maple, eastern redbud.
Pot colors were flat white, gloss white, silver and black for vegetables – a black pot (typical industry pot) was added for woody plants.
The soil was a typical bark-based nursery mix.
The plants were grown normally and evaluated after 4 months with roots being measured in 3 areas (the central core, the southern exposure and northern exposure)
In beans – the temperatures were lowest in flat and gloss white and greatest in black. Root density on the hot south side was reduced by 63 to 71% in black pots compared to the white.
In the heat-sensitive maple plants, soil temperatures averaged 7 degrees higher in black and green than the white resulting in a 2.5 times greater root density in the lighter colors. (more roots in lighter colors leading to healthier plants)
Redbud was chosen because it is pretty heat tolerant and the changes were not as dramatic.
Bottom line – avoid black and dark green pots for growing.
John W. Markham, Dale J. Bremer, Cheryl R. Boyer and Kenneth R. Schroeder
Kansas State University, Department of Horticulture, Forestry and Recreation Resources, Manhattan, KS 66506