Answer: The seeds are from the flowers that faded earlier this summer. To keep that from happening, prune your lilac back as soon as the flowering has stopped and the flowers are spent. If you leave the old flowers on the plant they will develop seeds. Lilacs begin to develop flower buds for next spring's floral display during the summer months. It's best to prune immediately after flowering has finished to give your shrub the rest of the summer to produce new growth and new flower buds for next year. To keep lilacs neat and compact, prune a few inches off, all over every year. If it is overgrown and in need of renovation, you can prune it back by about one-third to reduce its size.
Best wishes with your lilac!
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