Answer: Lilacs are pruned once a year, if needed, immediately after blooming. Periodically remove some of the oldest stems by cutting them off very short at the base. A rule of thumb would be to take out about a fifth of them each year. This will keep the plant vigorous. Also remove any suckers that are smaller than a pencil in diameter. You may also deadhead, meaning remove the spent flowers, if you wish.
Butterfly bushes are pruned in early spring about when the daffodils bloom. Cut away any winter killed stems, then prune back to about a foot in height. These bushes bloom on new growth of the season and pruning will stimulate additional blooming wood. An occasional pinching early in the season will help the plant stay bushier.
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