Answer: Hollies can be kept clipped like a formal hedge or can be allowed to grow naturally, in general they should not need much pruning.
In shade, they will naturally and unavoidably grow thin and leggy. If your plant is in a shady location, trimming will not make it grow dense, the regrowth will be thin also.
The best time to prune a holly is in winter while it is dormant. Then the spring growth will come in denser. The best way to prune, if needed at all, is to prune selective branches rather than shear it. You can tip back the branches to encourage them to grow denser starting from where you have cut.
If the I crenata is terribly overgrown, you can try trimming it back quite hard. This is risky because it may kill the plant, and keep in mind too that Ilex crenata is not a terribly fast grower so it will take time for it to look presentable again. It is too late in the season to do this now, wait until late winter 2007.
Good luck with your hollies.
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