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Gardening Tips: Clearing up confusion about pruning

If you prune when it is still warm, those dormant buds will get the signal to sprout and produce new growth
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Susan Richards

I was visiting with our neighbours last evening and the topic of pruning came up. It was suggested that I write another article to clear up some of the confusion homeowners have about this complex subject.

I mentioned a few weeks ago that pruning should stop once August arrives. The reason for this is that pruning stimulates new growth. By late summer, trees and shrubs have set buds for next season.

If you prune when it is still warm, those dormant buds will get the signal to sprout and produce new growth.

Since it is late in the season, new growth may not have a chance to harden off for winter. That tender tissue is very susceptible to winter dieback. Also, new growth may not have time to fully develop buds for next season.

Many gardeners want to cut back shrubs and hedges during fall cleanup since long, lanky branches can get broken by the weight of a heavy snow load. I do always recommend early spring pruning as the first option, but if you need to shape plants before the snow flies, be sure to wait until late fall.

Once temperatures are consistently cold, there is little chance that pruning will promote new growth. Plants have gone dormant; leaves have fallen from the deciduous trees and shrubs; growth has shut down for the season.

Just be aware that fall pruning creates wounds that don't have a chance to heal before winter sets in. You may observe some tip dieback next spring.

The best time to prune cedar hedges is in early June, once new growth is finished. You can shape again in mid to late July, if necessary. In late fall or early spring, only snip off any wayward branch.

There is also many questions from gardeners about when to prune hydrangea shrubs. This large family of plants has quite a few groups that are pruned in different ways.

Annabelle hydrangeas have big round, white flowers that are at their peak in July. Once they fade, they turn green and then dry to brown. You can leave this shrub unpruned until spring if you enjoy the look of the dried flower heads in the winter garden. If you would rather tidy up in fall, it can be pruned quite hard.

With this variety of hydrangea, you have the option of pruning the traditional 1/3 to 1/2 of the newest growth or if you would rather keep it compact, you can prune to a foot from the ground. All flowers are produced on new growth, so hard pruning doesn't damage this variety.

Paniculata hydrangeas are the ones with cone shaped flowers that are gorgeous right now. Most varieties start out with white flowers that eventually change to a shade of pink. These shrubs and small accent trees are the star of the late summer garden!

Once again, flowers can be left on the plants over winter. They are then pruned in late March or early April. Stick to removing only 1/3 to 1/2 of the newest growth on all Paniculata hydrangeas. They don't like to be pruned hard like the Annabelle ones do.

The most frustrating hydrangeas to grow in the north are the group that produce either pink or blue flowers depending on soil pH. All Summer Beauty, Endless Summer, Nikko Blue and Tinny Tuff Stuff are all in this category of macrophylla hydrangeas.

Some promise flowers on both old wood and new growth but in the north, we have a problem getting old wood to survive the winter. These shrubs often die right back to the ground, sprouting new growth from the crown.

I recommend no pruning in fall. Wait until spring, when you see where new growth is emerging from. Once you see it sprouting, prune off all dead wood that is not producing any growth at all.


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