No, like flowering bulbs, cutting the flowers makes for better flowers next year, because you prevent plant energy spent on growing seeds. I cut off all the flower clusters when they fade on my very young bushes, so they use energy on growing, not seeds. Lilac bushes SHOULD be cut, they are FOR being enjoyed where you want them in vases or being given away. Church flowers, nursing home friends, spread the flowers around! I get so many good memories of things, when I sniff smelly lilacs!! For your lovely bush in the long run, some judicious pruning is helpful to it. I try to keep the sucker sprouts reduced to a couple new ones instead of many, each year. A little renewal coming along if I want to take out an old stem. New stems often bloom very well. I look at the bush to see if old trunks are still producing flowers in quantity. Sometimes they get so tall, you can't enjoy the flowers, so taking out an old trunk makes the flowers more available, VISIBLE to people on the ground. Sounds mean, but pruning your bush is actually good for it, and the flowering you want in the future. Pruning is one of the hardest things I had to learn, but the great results after have made me a believer. Prune as soon as the flowers are done, won't bother next years flowers at all. I am trying some stem braiding, which I saw on some old bushes. Just braided up some sucker stems, tied near the top with string. Will take some time, years, but fun to try for visual interest on the bushes someday. Smashing or cross cutting the woody stems, does help the flowers drink better, so they last longer. Mine are just opening now, smells GREAT outside.

In general, shrubs that bloom in the spring and early summer can be safely pruned after flowering. These sorts of shrubs (Lilac, Forsythia, Mock Orange, etc...) bloom on wood that grew last summer, or 'old wood', and if you prune them before they flower, you are also cutting off the flower buds. Shrubs that bloom in the late summer and autumn (PeeGee Hydrangea, Butterfly Bush, etc...) should usually be pruned early in the spring. These sorts of shrubs bloom on 'new wood, growth that has formed during that growing year. While you don't want to prune too late in the year because it stimulates new growth when the plant is winding down, a good rule of thumb is to plan on pruning after flowering is finished. BP

I agree with Terrene; best to leave them standing until growth begins in spring, and the same goes for most summer-blooming plants. A lot of plants that we grow as perennials are actually sub-shrubs, and they benefit from being left alone until spring. Things like gaura, caryopteris, perovskia, mums, and most herbs, even the little ones like the thymes, all have a much higher survival rate if they're not cut back in fall. I actually cut back all my butterfly bushes this weekend, not because it's good for them but because the ones I have are wickedly prolific self-seeders, and I'm trying to kill them the easy way. It's too bad, too, because they had pretty, silvery, felty leaflets on the branches, and they DID look nice. If I could just keep them dead-headed in summer ... but they get way too tall for that to work here.

I can attest to the miss kim(syringa pubescens), although I honestly find it a little less satisfying than my syringa vulgaris(es?). I do like the small size, but the blooms are also not as colorful, think an icy pinky purple, and much smaller than the vulgaris blooms. Additionally, it blooms later than the standards. All of my vulgaris are in full bloom now and have been for a couple weeks. The pubescens has visible flower buds, but it appears as though it'll be a few weeks before anything happens with them. And IIRC, they're not quite as fragrant. But they stay small, in fact basically look like a shrunk down vulgaris... smaller leaves, smaller flowers, smaller stature.