Why? The pictures here illustrate the problem - the shrubs had walled us off from a lovely view of the garden.
Meyer lilacs are supposed to be compact, and I suppose for lilacs they are, but they were easily reaching 6 feet. (Obviously, they hadn't read the nursery catalogue which stated that their mature height tops out around 4 or 5 feet.) Actually, woody plant expert, Michael Dirr, the author of my favorite tree and shrub bible, the Manual of Woody Landscape Plants, says they grow 4 to 8 feet tall. I didn't prune them, and so they were headed for 8 feet. Clearly, they were overgrown.
The solution: off with their heads. Will the shrubs flower next year? Probably not because we pruned them so radically in mid-July, and they form next year's flower buds shortly after blooming. But I've seen spotty repeat blooming in late summer, so you never know.
The reason for our late pruning is that I changed my plan of attack. I was actually planning to rip the lilacs out and replace them with peonies and boxwood shrubs, both of which are lower growing. But that would have been a lot more work, and we would have missed their lovely scent in spring.
So when master pruner Bob May was here working on the boxwood hedge, I asked his opinion and he suggested cutting them back radically. "They'll be fine," he assured me. "You're a couple of weeks late to prune, but they've got enough time to grow leaves and recover."
The lilacs have grown new leaves and they look like they are recovering well - and we have our garden view back. Thanks, Bob, for suggesting this solution. I have more of these lilacs in other parts of the garden, and I'm going to be more diligent about pruning them to stay more compact.