How and when to prune flowering shrubs

(Photo Credit: beckstei via Flickr)

A plant’s shape is determined by nature, and no amount of pruning will change that; forsythia will always produce arching branches. (Photo Credit: beckstei via Flickr)

Pruning is one garden task that is done with either too much or too little enthusiasm by most home gardeners. Many people head outside on the first sunny spring day and chop away at any and every plant they find. Others, believing that a garden ‘thrives on neglect’, don’t do anything at all.

Perhaps the most important piece of advice regarding the selection of woody plants for your garden is ‘don’t fight nature’. Choose trees and shrubs suited to the area in which they are to grow. Before heading off to the garden centre, learn all you can about the maximum height and width, light and soil requirements of any plant you’re considering buying. Cramming a plant that naturally grows eight feet tall and wide into a four-foot space and then trying to trim it into shape will only lead to your frustration and, ultimately, the plant’s death.

There are, however, several good reasons to prune plants, including:

To enhance the natural shape of plant
The shape that a plant grows is determined by nature, and no amount of pruning will change that. For example, forsythia and bridal wreath spirea will always produce arching branches; rose-of-sharon will always grow in a vase shape; and weeping caragana will always produce drooping branches. If you try to prune your forsythia into a box shape, you will get new growth only at the tips of the plant with large, dead woody branches inside the shrub. Ultimately, the forsythia will produce fewer and fewer blooms each year.

To promote plant health
Plants are much healthier if you remove all dead, damaged or diseased wood. Pruning away older, thicker branches will give newer ones enough light and air circulation to prevent disease. Also, remove branches that are pest-ridden or rubbing together.

To increase flower and fruit production
Prune flowering plants and some fruit trees to increase the yield and quality of blossoms and fruit. If you want your lilac, for example, to be covered in blooms next year, remove the spent flowers to prevent the plant from putting energy into seed production. Some plants put so much energy into fruit and seed production that there might not be any blossoms the following year.

To encourage stem and foliage colour
Plants like yellowtwig or redtwig dogwood produce vibrant-coloured stems that are beautiful in the winter landscape. The colour is always brighter on new wood, so cut back old stems to the ground each year.

To maintain safety
It is always wise to remove from trees and shrubs any branches that could obscure oncoming traffic or road signs. Also, remove any split or broken branches that may come crashing down on cars or nearby buildings. Prune away branches that obstruct walking paths.

One concern gardeners often have is when to prune. Spring flowering trees and shrubs produce flower buds during the previous season; they should be pruned immediately after flowering so you don’t remove next year’s flowers. Summer flowering trees and shrubs should be pruned early in the spring when they are dormant.

Old roses (once-blooming) bloom on last year’s wood but hybrid teas, floribundas and polyanthas should be pruned in early spring. Modern shrub roses don’t need much pruning at all. Just remove any damaged wood and lightly shape the plant.

Don’t prune any woody plants in late summer or fall as this will promote new growth, which can succumb to winterkill. If you want to rejuvenate an old shrub that has become overgrown and woody, do this over a three-year interval. Cut back by one-third of the growth each spring.

It’s a good idea to invest in high-quality pruning tools, which can include secateurs, loppers, pruning saws, shears and pole loppers for tall branches. Choose the right tool for each job. Always ensure your tools are sharpened, as this promotes a clean cut and doesn’t crush or tear wood, which can cause disease. Sterilize the blades between cuts with rubbing alcohol to prevent transferring diseases from one plant to another.

Viburnum (Photo Credit: ndrwfgg via Flickr)

Viburnum (Photo Credit: ndrwfgg via Flickr)

Spring Flowering Shrubs (Prune after flowering)

  • Forsythia
  • Bridal wreath Spirea
  • Snowmound Spirea
  • Viburnum
  • Lilac
  • Mockorange
  • Purple Sandcherry
Rhododendrons and Azaleas

Summer Flowering Shrubs (Prune in early spring when dormant)

  • Annabelle Hydrangea
  • Pee-Gee Hydrangea
  • Rose-of-Sharon
  • Butterfly Bush
Blue Mist Spirea
  • Hybrid Tea, Floribunda and Polyantha Roses
  • Potentilla
  • Lavender


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