Copper coating avoids root-circling in container gardening
The containers can be painted with Spin-Out which contains copper hydroxide. The coating deflects the roots and they form a massive productive feeder root system. Marine paint is less expensive, but it has a very high toxic copper content and is not recommended. If you use marine paint, wear a mask during application.
In wooden containers the less expensive exterior latex may be used, mixing 6 tablespoons of copper carbonate in one quart of paint, or 3.5 oz. of copper sulfate in one quart of paint. It does not stick to plastic containers.
Spin-Out has been approved for edible plants, but the use of the other paints should be restricted to ornamentals, but sooner or later the soil will be returned to the garden where vegetables may be exposed to it. This method is therefore controversial.