Cut it back as far as you want without cutting off the bud union. It'll grow back, although you'll be without blooms for awhile. Modern roses bloom on new wood so you'll get more flowers sooner than you thought. You can keep it in check by pruning off any canes that grow where you don't want them.I have a couple of climbers I have to prune off canes all summer. They grow out into the yard and bite me as I drive past on the garden tractor.

Consider oakleaf hydrangeas for 3-4 season interest - they do tend to be large, but they are much more interesting as plants than most other hydrangeas. They are also native to the southeast so are pretty much plant 'em and don't worry about 'em. Not native, but very pretty, are Chinese fringe, loropetalum, which are evergreen here. They come in green leaf, purple, and many which are kind of a combination of purple and green. They can be left shrubby or limbed up to a tree form. They get white or hot pink witch-hazel-like flowers in late winter/early spring - in fact, mine don't seem to know when they should flower and ofter flower on and off all year. They will grow quite tall on their own, but to my surprise, look well even when the leader is trimmed so they stay small. Not shrubs, but evergreen (or plum) and just beautiful, esp. in some shade, are the tiarellas and heucherellas which you can plant under shrubs. I love mine more every year. They have subtly variegated leaves which can be green and plum with silver, and they send up small delicate flowers on long stalks (coral bells). In fact, I have cut leaves for bouquests - they are stunning. Welcome. I haven't been around lately folks - busy with a million projects, but do hope to drop in now and then.

Thanks Linda, I think I'll try pinching back some of the sedums to spread the bloom time out a bit. I do leave the seed heads on all winter but I like to watch the evolution of colors on them in the fall. I thought I would cut off all my next spring's blooms if I trimmed the spirea. Actually, I want to convince my husband that he isn't to whack the poor thing back. I'm the one who mows anyway. Last time he "trimmed it" it involved a chainsaw! :-) Maria

Some sources say to chop the whole thing back to about 6 or 8 inches high. I would do that now, if I chose to go the more drastic haircut route, because to do so in the wintertime or even fall could run the risk of new shoots getting freezer burnt. Especially as you are in Z5. The other method for really old thick lilacs is to chop off one-third (or in your case, one or two) of the really thick old growth this year, then another one next year and so forth. This preseves more option of continuous bloom, if any. Personally I would use the former method. Also, lilacs like sweet soil, so a bit of lime or wood ash might be in order if your soil is acidy.