Answer: Annual pruning is the best way to keep lilac bushes healthy and full of blooms. Failing that, you can renovate old lilacs.
We recommend the three year plan. A lilac shoot takes about three years before it produces a flower. So plan to eliminate 1/3 of the shrub each year, selecting the oldest stalks. Cut them down to just above the level of the soil. As you do, allow new shoots to grow to replace the old ones. By the end of three years, the entire shrub will have been replaced, and you will not go without lilacs for that period of time. Then, continue the cycle each year.
If life with your overgrown shrub has just become unbearable, remove all old stock and leave just new shoots. This is pretty drastic. And, you will go a couple of years with out lilac flowers. But Lilacs are hardy. As long as there are a few healthy new shoots, they will grow back.
Rose bush pruning is usually done in the spring, just as the buds begin to swell. To keep the shrubs under control, choose the best 3-5 canes and prune the rest out. Of these 3-5 canes, prune them down to 18-24" to a bud that's outward facing. Pruning this way will provide an open center to help keep the roses disease free. Then, during the summer when you're deadheading spent blooms, prune the flowering stem down to a 5-leaflet leaf. This is where a new flowering stem is most likely to develop.
Best wishes with your landscape!
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