Below are pruning tips from tree and shrub expert John Shearin:
Indeed, it’s best to have a reason to prune before picking up the loppers and lopping away willy-nilly. So here are some good reasons for pruning in a non-willy-nilly fashion.
- To remove the 3 D’s – dead, diseased and damaged branches or stems. Also in this category would be a C for crossing branches (those that cross other branches or stems) because that crossing and rubbing against will cause one of the 3 Ds sooner or later. The 3 Ds can be pruned away any time of the year.
- For flowering shrubs, to get a fuller plant and more flowers, rejuvenation pruning is called for.
- Sometimes to prevent disease. One example is the dreaded lilac bore, damage from which can be reduced or prevented or removing the oldest canes
- Evergreens can be pruned really any time of the year except late summer/fall.
- Spring-flowering shrubs and trees are best pruned soon after they flower. If pruned right before flowering, you’ll be cutting off the buds that are about to turn into flowers. So forsythias, azaleas, rhododendrons, lilacs, early blooming hydrangeas (lacecap and mophead types especially), early blooming spireas, and weigela should be pruned – if they need pruning – before summer.
- Summer and fall-blooming trees and shrubs like crape myrtle, oakleaf and Annabelle hydrangeas, caryopteris and butterfly bush should be pruned between the time they bloom and early the next spring – so NOW if you haven’t already. After this month you run the risk of removing their new buds for this season.
- Shrub roses are best pruned in February or March – President’s Day is the usual starting date for rose-pruning. Old-fashioned climbing roses and most ramblers flower only once a year, usually in late spring or early summer, so should be pruned right after they finish blooming.
How to Prune Roses
John demonstrated how to prune a rose (except for climbers), by cutting above existing buds or forks in the branch, and cutting at a 45-degree angle. Shrub types should be cut back to about 18″ off the ground and tiny canes removed entirely. Prune out any canes that criss-cross each other to ensure good air circulation and healthy stems. A dab of Elmer’s Glue on the ends of the cut canes can help discourage rose cane borers, a type of beetle.
Knockout and other types of landscape-style roses can be pruned back to close to the ground if you want to control the size – they’re very amenable to pruning. Knockouts will also rebloom better and faster if they’re deadheaded – their spent flowers removed back to the next stem. For many years rose-growers were told to dead-head rose flowers back to a “true leaf”, which means a stem that held 5 leaves. Now that that advice has been debunked, we’ve stopped counting leaves to find the “true” one; just prune back to where the next stem starts.
Climbing roses are different. Correct pruning for climbers is designed to trick the plant into growing where YOU want it to grow and blooming where YOU want it to bloom, too – not just at the very top. Here’s a video from a plant expert at the New York Botanical Garden that shows you how to do that.
Shearing, if you Must
John, and most woody-plant experts, avoid shearers most of the time but true to his name (Shearin!) John does shear occasionally, and demonstrated the technique on this topiary juniper.
Another plant that’s amenable to shearing is the yew Though many boxwoods are sheared, John doesn’t shear them because doing so leaves the remains of half-chopped-off leaves. Asked about the difference between electric and manual shears, John answered: speed, which is a good thing if you’re in a hurry but in situations where you want to really see what you’re doing, not such a good thing, so manual shearers may be best.
A Word about Conifers
So we’ve learned that yews can take shearing, but they’re unusual among conifers for their ability to support new growth from the inner branches and main trunk. Hemlocks are also. Other conifers can only be trimmed at the outer few inches only.
A safe generalization about conifers is that when it comes to pruning, they’re a very unforgiving bunch! So do the research – by putting “prune” and “Mugo pine” or whatever the plant name is into that search box and reading sources that end in “edu” or “gov”. Also, Fine Gardening Magazine has good advice from experts on their website.