Answer: The most common reasons for lilacs to fail to bloom are growing them in the shade and/or pruning at the wrong time. Lilacs are sun lovers and need full sun all day long to bloom well. They bloom on wood that grew the previous year, so the only time to prune them is right after they bloom. At that time, remove any new shoots from the ground that are smaller than a pencil in diameter. If your lilac is five years or older, you could also remove a few of the oldest branches by cutting them off at the ground. Doing that each year whis will stimulate vigorous new growth. I hope this helps you trouble shoot.
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