Wednesday, December 2, 2020
Dec. 2, 2020

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Gardening With Allen: Prune shrubs bottom to top


I have shrubs which are blocking my windows and have grown over walkways. Is this a good time to prune them or should I wait until spring?

Except for spring flowering shrubs like rhododendron, azalea, lilac, spiraea and forsythia, this is an excellent time to prune. Spring flowering shrubs have already formed flower buds for next year. Pruning now would remove many of those flowers. The best time to prune flowering shrubs is right after they bloom.

I prune almost all my shrubs one branch at a time. This keeps their natural shape and thickness. Pruning with power clippers or shears causes plants to develop many more branches than is normal. There are only a few plants like hedges and upright conical junipers that look good with thick growth.

I normally start at the bottom when I prune a shrub. The lowest branches are pruned to the width you want the shrub to be when you have finished pruning. In some cases they are only pruned enough to restore uniformity. As you move up, taper the shrub so branches are pruned shorter as you work up the shrub. Upper branches are pruned the most because they grow the fastest. It is important to prune upper branches so they do not shade lower ones. When lower branches are shaded they lose their leaves. Shrubs develop what I call a “chicken leg effect.”

Start by selecting one of the longest branches and reach down inside other branches. Cut it a little shorter than the size you would like the shrub to be after pruning. Select another long branch and do the same with it. The shorter adjacent branches hide the stubs.

In most cases shrubs should not be reduced in size by more than a third. Be careful not to prune needle evergreen shrubs like juniper and pine so that all the green growth is removed. Evergreens will not grow new leaves on branches that are cut so short that there is no leaf growth remaining.

Broad leaf shrubs can sometimes be pruned more than a third, but it may take more than one season for them to return to normal size.

Trees can also be pruned now. Extra long branches can be shortened, just like shrubs. Lowest branches can be removed as the tree grows taller. When branches are removed completely, a 1/4 -inch stub should be left. This stub is referred to as a collar because it looks like a shirt collar. The collar contains the healing tissue that the tree uses to heal the wound.