Answer: There are two ways to renew a lilac. One is to cut it off as close tot he ground as you can and let it regrow completely. The other is to prune it over three years, each year taking a third of the oldest growth by cutting it at the base. In three years' time you will have all new growth. Routine lilac care would include removing all suckers smaller than a pencil and occasionally removing some of the oldest stems so that it never needs to be renewed. All lilac pruning should only be done in the spring right after it blooms.
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