Many perennials and shrubs benefit from spring pruning. Pruning helps stimulate new growth, re-directs energy for flower and fruit production, and keeps plants healthy. You may also want to prune certain plants to control their size and shape.

How deep you delve into the topic depends on what you are trying to accomplish. It can be as simple as removing dead stems from your rosebush or as complicated as training an apple tree to grow flat against a wall or trellis (espalier). For most basic pruning tasks, however, the trick is knowing not only how, but also when to prune. The answer varies for different plants.

Many common flowering shrubs, such as forsythia and lilac, bloom on the previous year’s growth. That’s an important point, because if you prune these plants in early spring, you won’t get any flowers at all during that growing season. Forsythia and lilac both should be pruned after they bloom. Most hydrangeas also bloom on old wood.

Other plants bloom on the current year’s growth and can be pruned in late winter or early spring to remove dead wood, help them stay full, and ensure abundant blooms.

Buddleja (butterfly bush) is a good example. Every year in late February or early March I cut my buddleja down to about 18 inches off the ground. And each year the plant grows about six feet tall and is covered in blossoms from mid-summer through fall—and yes, butterflies love it. If I didn’t cut it back, though, it would grow tall and spindly and would have fewer flowers. Even after flowering, I continue to cut off spent blossoms every couple of weeks to encourage re-blooming.

Your spring regimen should also include clipping off spent woody stems and dead flower stalks and foliage from perennials, as well as the last year’s growth on ornamental grasses. Local horticulturist Jenny Aiello recommends cutting lily turf and nepeta (catmint) down to 2 inches off the ground in early spring. “But wait until the weather gets warmer to cut lavender, because the branches can dry out,” she says. “The same goes for rosemary if it has made it through the winter.”

If you prune a plant at the wrong time or in the wrong way, you can do more damage than if you hadn’t pruned at all, so be sure to learn as much as you can about your particular plant and consult a reliable source of information before picking up those loppers.

Luckily, many great books and websites can teach you when to prune particular plants, the best tools for different pruning jobs, and proper techniques. For starters, check out Texas A&M University’s excellent Aggie Horticulture site. Lee Reich’s "The Pruning Book" (Taunton Press, 2010) covers everything from shearing common hedges to mastering the arts of topiary and bonsai—which are, after all, just more complicated forms of pruning.