Tips For Summer Pruning

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pruning lilac

By far, the most advice I get asked for is on the subject of pruning. It can be quite a complicated subject because so many trees and shrubs have specific requirements. Here are some tips to help you out.

Most flowering shrubs can be tidied up after they finish blooming. Forsythia, Mockorange, Sandcherry, Spirea and Weigelia are a few examples. However, the only time a lilac should be pruned is immediately after flowering. This shrub, as well as rhododendrons and azaleas, set flower buds on the end of new growth once blooms fade. If these plants are pruned in the fall or spring, you are cutting off the flower buds!

If possible, prune off each dead flower cluster with hand shears. Cut on a slight angle right in front of a bud. Try not to leave long pieces of stem ahead of buds.  These stem sections have to wither away and fall off before the pruning cut can heal properly.

If buds are positions in several directions along the stem, cut in front of an outward facing bud. This directs new growth to the outside of the shrub rather in towards the centre. Branches growing inwards will often tangle or cross each other and rub. Branches that rub against each other will wear bark away, leaving an spot for insects and disease to enter the stem.

Some flowering shrubs are not pruned after blooming because they have an interesting berry, seed head or flower cluster that dries nicely on the plant. Dogwoods and Viburnums have nice berries. Sumac and Ninebark have attractive seed clusters. Some roses have beautiful hips that feed the birds in winter. Hydrangea flowers dry well producing an interesting effect for the winter garden.

Broadleaf evergreens such as Euonymus and Boxwood can be pruned once right now. Remember the one-third rule: cut back one third of this year’s growth to encourage a healthy, bushy plant. Be sure to use sharp shears when shaping. Dull pruning tools leave ragged cuts with leaves that turn brown and look messy.

July is a good time to shape hedges. The first flush of spring growth will have finished. Many deciduous and evergreen hedges can be shaped now: Caragana, Alpine Currant, Honeysuckle, Cotoneaster, Privet, Boxwood, Cedar, Yew and Spruce.

Try to put a slight taper on the hedge so that the bottom is wider than the top. This shape allows sunlight to reach all parts of the plant. If the top is wider than the bottom, the lower foliage gets too much shade and dies away. Your hedge can end up with a bare bottom!

Pines should not pruned fall or spring. Like lilacs, they only have buds at the terminal end of the new growth. The perfect pruning time for Mugho pines is when the new growth resembles a candle; before the needles open up. If you missed pruning your pines at that stage, do it right away! There will still be time for the plant to produce buds at the end of the new growth.

Now is also the time to prune other evergreens: cedar, yew, spruce and hemlock. Unless these plants are forming a hedge, try to avoid cutting the main leader. You want one main shoot growing tall and straight right up the centre of the tree.

If you have maples trees that need pruning, do it now. They are one of the trees not pruned in spring when sap is running. Look for branches that hang too low or cross and tangle in the centre of the tree. Determine which branch that has to go and prune accordingly.

One final word of caution when doing any tree pruning. Allows look up and assess the area before you start. Never prune close to overhead lines! Contact your service provider if there is an issue that has to be dealt with near lines.

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About Me

I began my journey in horticulture in 1982 after graduating from the Humber College Landscape Technician program. At that time, I lead a talented crew of landscapers, taught evening courses in horticulture and had my own landscape design and consulting business. Then I ventured into the garden centre world. I’m lucky enough to be leading the friendly and knowledgeable team at New North Greenhouses. 

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