Which Plants Should You Prune in Fall?

In just six to eight short weeks, my garden shifts from glorious green to a golden jubilee. It is beautiful in every season, but I always miss the flowers when they go.

Once the plants in my garden have gone mostly or completely dormant in late fall, it’s time to prepare for winter. I grow a wide variety of annuals, perennials, trees and shrubs in this border, and I don’t treat every plant the same. I listen and observe, letting the plants tell me how they’d like to be handled, and I pair that with some solid horticultural knowledge. Follow the lists below and you can’t go wrong.

What I don’t prune in fall:

• Anything evergreen or semi-evergreen, whether it’s a perennial, tree or shrub
• Woody perennials like Russian sage, lavender, perennial Hibiscus and St. John’s wort
• Any perennials that look pretty with a fresh dusting of snow, like the rusty brown plumes of Astilbe
• Shrubs with berried branches or colorful stems that bring vibrancy to the winter garden
• Plants that provide food or shelter for birds and other critters over the winter such as ornamental grasses
• Plants with hollow stems like delphiniums – to prevent moisture from traveling down the stems into the crown of the plant

Any shrubs that bloom on old wood (the previous season’s growth) including azalea, sweetshrub, forsythia, bigleaf hydrangea, mountain hydrangea, oakleaf hydrangea, lilac, ninebark and weigela. Trimming them in fall would eliminate next year’s flowers.

What I do prune in late fall:

• Any perennials that have gone completely dormant and will have mushy foliage if I leave it through winter like hosta, tall garden phlox, brunnera, lilies, bleeding hearts, daylilies, Ligularia, catmint, bee balm, peonies and salvia. Slugs love to lay their eggs in dormant foliage like this.
• Any perennials or roses with diseased foliage – bag and dispose of these instead of adding them to your compost or brush pile
• Any plants with broken branches or those that have grown over my pathways, windows or roof

Notice my “don’t prune” list is much longer than my “do prune” list for fall. Spring is a better time to prune many types of shrubs and evergreen perennials to get them off to a good start for the new season. Remember, shrubs don’t need to be pruned to bloom and grow. If you’re not sure when to prune, a good rule of thumb is just don’t do it!