Developing an eye for pruning perennials is rather like learning to appreciate fine art: Studying why an artist placed a brushstroke a certain way is helpful to understanding the work of art, but sometimes you just have to stand back and look at the whole.
In other words, it's helpful to the gardener to read everything possible about pruning and to ask lots of questions, but when you're standing there on a sunny morning with the shears in your hand you simply have to feel what the garden needs. Pruning is practical, certainly, but develop your eye by looking at gardens you admire to see what makes them beautiful. Don't be afraid: pruning is a good thing.
When should I prune my perennials?
Most woody perennials benefit from pruning in the early spring just before the plant breaks dormancy. You're unlikely to hurt the plant if you neglect your pruning duties even until mid-summer. Once the leaves turn and autumn has arrived, set pruning aside until next year unless something major needs to be done.
If you're a pruning newbie, you may want to take out the shears after the plant has bloomed because it's easier to see what you're doing. That's just fine as long as you're at least a month before autumn. Better to do the job late than not at all.
For the first three or four years after transplanting woody perennials, trees and shrubs, or fruit plants, you should keep pruning to a minimum. Once they're well-established you can take a heavier shears to them and really begin to shape your garden. Always try to prune older wood rather than new growth, but don't be afraid to lop off a new branch if it's in the wrong place.
Heavy pruning entails removing one-third of the plant's growth. Yes, that's a lot. If pruning has been neglected, perform such heavy maintenance only in the late winter. After that, you can just clip off what's necessary to maintain the health and beauty of the plant.
What is the purpose of pruning, and will it hurt my perennials?
You'll only benefit your perennials by pruning away dead wood, broken branches, crowded branches, and anything that looks unattractive. Prune with a purpose: stand back and look at the plant as an individual and as part of the landscape. Clip off one branch at a time until you get a good feel for how it should look.
Pruning perennials promotes clean, new growth and reduces legginess. Many perennial shrubs bloom only on new wood and you can encourage that growth through planned pruning. Pruning perennials also helps them survive heavy snowfalls because a well-structured plant can withstand the weight.
Removing a few branches opens the inside of the plant to air and light, giving it a growth boost and keeping insects and molds at bay. Insects and molds love a wet, tangled mess. Should a woody perennial drop leaves from certain branches during the season, investigate the cause and clip off anything that's diseased or insect damaged.
What parts should I prune off my woody perennials?
The goal with pruning perennials is to thin and shorten branches, but sometimes you'll need to shear off whole branches. Begin at the heart and base of the plant. Dead and diseased branches must go first. Prune branches that are close to the ground to minimize rot and disease, and open up the interior to light and air by removing whole branches close to the trunk or stem.
Now stand back and take a look. Any nodes or twigs that are growing toward the ground can be clipped off. Clip the tips of branches to rein in a shaggy look and shape the plant nicely, but don't take more than one-third of an individual branch. Crossed twigs should also be sheared off, as well as anything tangled with another plant or rubbing on a nearby structure.
Should I prune soft perennials?
Perennials that die back to the ground and regrow each spring benefit from careful pruning during the growing season. Clip leggy plants before they bloom to encourage bushy growth. Cut off a few buds or blooms to encourage larger blooms. Thin crowded stems to encourage air circulation and healthy growth.
Glen Witney advises pruning yellow or dead foliage from soft perennials throughout the season. This keeps the garden looking vibrant and inviting. Likewise, giving perennials a haircut after blooming encourages strong green growth and better winter survival.
What's the difference between deadheading and pruning?
Deadheading perennials is a type of pruning where the gardener removes spent blossoms. Unfortunately, most perennials will not rebloom unless you're very lucky, but deadheading keeps the plants looking clean and green. When you deadhead, you're only removing the flower stem back to the main branch.
What tools do I need to prune perennials?
You could spend a million dollars on gardening tools, right? You probably won't need a chainsaw, even if it is a fun tool. Here are a few that might come in handy for pruning jobs and other gardening activities.
Long-handled lopper for branches up to 2-1/2 inches in diameter; long handles give good leverage.
Cushion-handled hand pruner for branches up to ¾ inch in diameter.
Extendible (telescoping) pole trimmer for pruning trees.
Cordless hedge trimmer for easy work all over the yard.
Hand saw for cutting down a whole plant or dealing with big branches.
Small bypass pruner for every clipping job from pruning to deadheading to harvesting herbs.
Before laying down your credit card, make sure any tool you buy fits your hands. Spring loaded tools might seem nice but can get sticky if you don't clean and oil them properly. Keep all your pruning tools sharp and dry for years of help in the garden.
Are there any other tips I should know?
These are the overall basics but you should always check information on individual plants to learn what they need and like. Maintaining a garden is like enjoying a large art gallery—each plant has its own personality and idiosyncrasies, and they are beautiful as specimens and as part of the larger landscape.