Answer: It does not damage the shrub to cut blooms for bouquets, but it can ultimately change the shape of the shrub if you cut a lot of them or if you cut them all from one section of the bush. If you look carefully, you will notice that cutting away a branch causes the shrub to subsequently branch more.
Lilacs are best pruned in the spring either during or right after flowering. To keep the plant vigorous, some of the oldest stems should be removed each year by cutting them at the base. You would also remove any new shoots thinner than a pencil by cutting them off at the ground. Use a sharp pair of pruners to cut your bouquets and a sharp set of loppers or a saw for the larger stems.
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