I don’t know that I would have a large old lilac in a Washington garden; it is simply not ornamental enough outside its week or two of bloom. But the standard pruning regimen is to remove about a quarter of its oldest branches and suckers each year, but do this in early May, when you should also take off the faded flowers before they form seed.
Now is the time to attack the roses. The high-performing landscape roses don’t need the delicate pruning that attends hybrid teas and grandifloras — they can be chopped back with hedge shears and will shoot back and bloom. But in our subtropical climate, it just seems right to devote the same care to pruning a workhorse like Knock Out as you might something more delicate and prone to the dreaded blackspot. You must have thick, thornproof gloves for this job. My initial prune is with the loppers, cutting the bush back and removing old and sick canes entirely. Ideally, you want half a dozen or so healthy canes forming a bowl around the crown. Use the hand pruners to cut them down to about 20 inches or so, cutting them half an inch above an outward facing bud. All this will promote an open and healthy habit come May. Make sure you pick up all of last year’s leaves, which harbor blackspot spores.