Answer: Here are several reasons why your lilac might not be blooming. The most common reason for a lilac not to bloom is that it was pruned at the wrong time of year. Lilacs bloom on old wood that grew the year before, so the best time to prune is right after it blooms. Pruning later in the season, or pruning in early spring, will remove flowering wood and flower buds.
Some lilac varieties are alternate bloomers, meaning they bloom more heavily one year and less so the next -- although it would not be quite so extreme as none at all.
Although it would be unusual, it is possible a spring freeze damaged the flower buds. If this happened, you would probably notice other lilacs in your neighborhood are not blooming this year.
Based on your description I am not sure if you mean the shrub is not blooming, or if it is not growing at all. If it is not growing at all by now, then sadly it may be dead. Lilacs are very winter hardy, so I would not expect a problem with that. You might check the roots for signs of vole activity, sometimes this winter time damage goes unnoticed until the plant fails to grow in the spring.
YOu can check to see if it is alive by starting at the branch tips and working your way down the plant. Live wood will be supple with green just inside the bark and plump buds. Dead wood will be off-color gray or brown, the buds will be shrivelled and dry or will have fallen off, the wood is brittle and will snap in your hand. Trim off any dead wood. If there is any live wood, it should be able to recover and regrow.
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