Holes in the bottom of a container sometimes aren't enough, Sue. I often have to drill holes in the sides of a container because the roots have plugged up the holes at the bottom. It doesn't become apparent until after a heavy rain, when i suddenly notice that the water is not draining away and the plant is in danger of becoming waterlogged. If the plant and the container are so large that I can't lift them to prune the roots, I have no choice but to drill holes in the sides of the container.