Useful Quotes from the Linked Payne’s Nursery Piece:
Don’t Prune: Don’t prune forsythias or lilacs until they’ve finished blooming this year. That’s because they blossom on one-year old wood. If you prune these bushes before their spring show, you won’t get any blossoms this year.
Don’t prune your roses until you see new buds forming on their stems. Stems that look dead may actually be sleeping.
Don’t prune fruit trees unless you’re sure you’re not pruning out fruiting branches.
Do Prune: If you didn’t do it last fall, cut back last year’s dead growth from perennials. It’s also time to cut butterfly bushes (Buddleia) way back, to within a few inches of the ground. Don’t worry, they’ll easily regain 6 to 8 feet of growth in a season, and the hard pruning will make the plants less leggy and much more floriferous.
Unmulch Your Perennials & Roses: Pull the mulch away from these plants so they can start acclimatizing themselves to the spring weather, and to prevent the development of fungus diseases as the weather warms. Be gentle — it’s easy to break off emerging shoots, particularly on peonies. Bear in mind you may have to recover some plants quickly if there is a late freeze warning. Heavy mil plastic sheeting works great for this purpose.