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Growing Concerns: Wondering whether to cut back the garden this fall?

October 8, 2018

I have gotten quite a few questions about what should be done for fall cleanup in landscape beds. Here are some ideas to address these questions.

Should perennials be cut back in the fall or the spring?

This is really a matter of personal preference. Some perennials, such as hosta and daylilies, lay down flat and are easier to clean up in the fall before they are smashed into the ground by winter snows.

Many perennials, however, are more rigid and will stand erect for most of the winter. I prefer to leave these standing until spring to add winter interest and to benefit birds. In natural areas, seeds from perennial plants are an important food source for wildlife. In the landscape it is really in the eye of the beholder to determine what they find most aesthetically pleasing.

My shrubs have become very overgrown. Can something be done to reduce their size or do they need to be replaced?

This question really needs to be addressed by separating deciduous shrubs from evergreen shrubs.

Renewal and rejuvenation pruning are two methods to reduce deciduous shrubs. The preferred method depends on the shrub species and particular situation.

Renewal pruning involves thinning the shrub by removing about one-third to one-half of the thickest stems. These will also be the tallest, so the shrub will be reduced in the process. This preserves some blooming wood on spring blooming shrubs and will promote new shoots from the ground the next growing season.

If this is done annually, you will never have any canes older than three years in the shrub, which helps maintain an appropriate size and preserves flower wood from season to season. This approach does take two to three years to accomplish the full effect.

Rejuvenation involves cutting the entire shrub back close to the ground. This is often done on smaller summer blooming shrubs, like spirea and potentilla. They bloom on new wood, so even if cut all the way to the ground they will bloom the following season. Spring blooming shrubs can be rejuvenated but they will not bloom for a couple of years afterward.

The ability to reduce evergreens really depends on past pruning practices. If they have been sheered repeatedly, which creates a dense layer of foliage that shades out inner growth, reducing them is usually not possible. If they have been pruned to a more natural form, most evergreens can be reduced to some extent.

It is important to start when they are small and to selectively prune every year to maintain the size of evergreen shrubs in landscape beds. If done properly, these shrubs will retain foliage well into the shrub and be much healthier than tightly sheered plants.

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