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To Trim or Not To Trim?

Category: Gardening Tips, How-to Guides | Posted by: Mike Riesenberg

It is finally time to get outside and get to the yardwork we have been dreaming of doing, or dreading doing, all winter long.  One item on the to-do list is trimming shrubs. And so a frequent question we field this time of year is:  When do I trim my shrub(s)?  All shrubs are not the […]

It is finally time to get outside and get to the yardwork we have been dreaming of doing, or dreading doing, all winter long. 

One item on the to-do list is trimming shrubs. And so a frequent question we field this time of year is: 

When do I trim my shrub(s)? 

All shrubs are not the same. Here is a quick refresher on what to trim now and what to trim later.

Shrubs that can and should be trimmed at the beginning of each growing season (February, March, April) include:

Some roses (Knock Out, Home Run, Drift, Hybrid Tea); paniculata hydrangea (Limelight, Little Lime, Vanilla Strawberry); spirea; weigela; potentilla; barberry; boxwood; holly (evergreen and deciduous); taxus (yew); and ornamental grasses.  Trim back ornamental grasses as close to the ground as possible and do so before new growth begins.

It is best to selectively trim big leaf macrophylla varieties of hydrangea such as the Endless Summer series after re-growth begins, removing only dead branches.  However, these newer varieties of macrophylla hydrangea (such as Endless Summer) can be trimmed to shape early in the growing season as they will bud and bloom on the current year’s growth in addition to last year’s growth.

Trim all deciduous (not evergreen) shrubs to desired shape and size. Trim evergreen shrubs deliberately – do not trim past the point where there is not foliage. Complete trimming for the above mentioned plants early in the season, before plants put on a considerable amount of new growth – this will ensure that valuable energy stored in the root system is not wasted on parts of the plant that will be removed.

Now for the shrubs that should be trimmed later in the season, soon after they have finished flowering:

Forsythia; lilac; viburnum; fothergilla; azalea and rhododendron; and climbing roses to shape and encourage re-bloom. Trim these shrubs within two to three weeks after they have finished flowering. Any later than two to three weeks these plants will have set buds or be in the process of setting buds for the following season. Trimming after buds have set will eliminate or decrease the number of flowers the following year.

Old-timey macrophyla hydrangeas (Nikko Blue, Lady in Red, Glowing Embers) and oakleaf hydrangea (Ruby Slippers, Snow Queen, Alice) should only be trimmed after they flower as these varieties flower on buds set the previous year. Trim these shrubs back within a few weeks after the flowers have begun to dry out.

What about needled evergreen shrubs such as Globe Blue Spruce and Dwarf Norway Spruce? 

It is best to trim these soon after they have pushed out their new growth for the season. Enjoy the soft and colorful new growth like you would a flower, then trim away as this growth begins to harden-off and before new bud-set, usually around the 4th of July.

The list above is not all-inclusive. Not sure what to do? We welcome questions about what to prune, when to prune, and will the Cincinnati Reds do better than .500 this year? We can answer your questions about trimming shrubs, but maybe not about the Reds! 

Call us at 513-385-3313 or email us at INFO@WHITEOAKGARDENS.COM.

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