Answer: I wouldn't cut them down to the ground - you may shock them to death! However, you can safely prune off one third of the plant without harm. If your hollies are still sparse and misshapen next spring you can take another one third off. Wherever you prune your holly will develop two new stems so that will help them fill out and become denser. In 2-3 years they will be a nice compact size and full of branches. Enjoy!
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