Spring is the time to prune woody plants to remove damaged or diseased branches, to rejuvenate old shrubs to promote flowering or improve their shape, or to ensure safety. Yet pruning is a task that daunts gardeners because they're afraid of making a mistake. Take heart. You're unlikely to kill the plant, and any bad errors should eventually disappear as it grows.
In fact, pruning stimulates growth. When you cut back a shoot, you cause buds on the remaining part of the branch to break into growth. Note, however, that a characteristic known as apical dominance causes the topmost buds to grow the fastest and the longest. This is useful if, for example, there is a hole in a tree, shrub or hedge that you want to fill. By pruning surrounding branches back to a bud pointing toward the hole, you can encourage growth into the empty area.
Bush whack
Shrubs that bloom in spring and early summer should be pruned shortly after they flower. Some species grow slowly and only need to be pruned occasionally, but if they're overgrown, now is the best time to shape them. Shrubs that bloom later, in summer or fall, normally flower on the new season's growth and should be pruned in spring to promote a vigorous crop of new shoots (thus encouraging abundant flowering).
Prune certain shrubs (list provided below) before their buds break in early spring. Names marked with an asterisk should be cut back hard; for the rest, simply remove the oldest branches as needed.
Shrubs such as yellow-twigged and red osier dogwoods (Cornus alba and C. sericea) and ‘Flame' willow (Salix ‘Flame'), which are all grown for their brightly coloured bark, should be cut back hard every two or three years, since their new growth has the brightest colour. Treat yellow-leafed elderberries, such as ‘Sutherland Gold' (Sambucus racemosa ‘Sutherland Gold') in the same way.
Because spring is also the time when sap flows, tree pruning should be kept to a minimum. Yet early spring is the best time to deal with tree branches damaged by winter winds. If left untended, these broken branches can fall, tearing off a strip of bark and leaving a large, slow-to-heal wound that is an entry point for disease and insects (not to mention the danger to anything—or anyone—directly below). If pruning means taking both feet off the ground, it's best to hire a certified arborist. But if the branch is small or within reach, you can remove it yourself. Here's how.
Before you start the final pruning, remove the bulk of the broken branch to lighten weight and lessen the risk of tearing the bark (see illustration). Close to the trunk, but not right against it, the branch should suddenly flare out. This is the branch collar, which contains active cells that will start to grow, sealing off the injury and allowing the wound to heal. Carefully cut off the stub of the damaged branch just beyond the branch collar (out from the trunk beyond where the rough, thicker bark ring is located). Make a small undercut first, then cut down from above to meet the initial cut (this prevents the bark from tearing). Don't use wound paint; it's been shown to slow healing and increase the chance of infection.Apart from dealing with broken branches, the only other spring pruning you need to do on trees is to remove the water shoots or spouts, which are those fast-growing, thin, vertical shoots without side branches. They appear on many species but are especially noticeable on apples and crabapples, and most frequently arise on branches that grow almost parallel to the ground.
Rose and clematis cuttings
Depending on where you live, roses may need fairly severe spring pruning to remove winter injury, or just a light shaping. For example, most of the shrub roses, such as rugosa hybrids and Explorer and Parkland roses, simply need to have their dead wood—and likely some of their oldest shoots—removed. On the other hand, if there's winterkill, hybrid teas and floribundas should be cut back to healthy wood. Don't be in a great hurry to tackle this. If left alone, seemingly dead shoots can suddenly show signs of life. It's best to wait until their buds have started to swell, then prune directly above an outward-facing bud so the new shoot grows away from the centre of the plant.
Clematis is trickier. They flower at different times throughout the season and their pruning requirements vary greatly, with some being cut almost to the ground in spring and others not being pruned at all at this time. In general, the late-flowering types are pruned in spring, but the degree of pruning can vary. Consult any good clematis book for specific directions on what to do for your varieties. Tips for spring pruning other popular plants:
Climbing roses: Shorten old growth back by about one-third.
Rambling roses: These flower on old wood; don't prune until they've flowered.
Vines: Prune to keep within bounds before leaves unfurl.
Conifers: Don't cut back hard because they seldom regrow. New growth can be hand-pinched back by about one-third while it's still soft.
Perennials
Stems left to collect snow over winter should be cut back close to the ground before new growth starts. Cut back woody perennials, such as Russian sage (Perovskia atriplicifolia) by one-half to one-third to promote new growth. Tall plants, such as delphiniums, will give a better display of flowers and have stronger stems if the number of shoots is limited. Remove thinnest shoots when they're about 15 centimetres high. Leave two shoots on a young plant and seven or eight on a mature one.
Shrubs you can prune worry-free
- Japanese angelica tree (Aralia elata)
- Butterfly bush (Buddleja davidii)*
- Bluebeard (Caryopteris x clandonensis cvs.)*
- Bush honeysuckle (Diervilla spp.)*
- Common witch hazel (Hamamelis virginiana)
- Rose of Sharon (Hibiscus syriacus)*
- Annabelle hydrangea (Hydrangea arborescens ‘Annabelle')*
- PeeGee hydrangea (H. paniculata ‘Grandiflora')*
- St. John's wort (Hypericum spp.)
- Potentilla (Potentilla fruticosa)
- Ural false spirea (Sorbaria sorbifolia)*
- Spirea (Spiraea—most species and hybrids)
- Snowberry (Symphoricarpos albus var. laevigatus)
- Five stamen tamarisk (Tamarix ramosissima)*
