Proper Perennial Pruning Promotes Perfect Plants

Well, perfect may be an overstatement but there are many pruning methods that will greatly improve the performance of your perennial garden.  Most home gardeners (and gardening professionals alike) are unaware of the pruning techniques that can be utilized on perennials.  Pruning, in general, is a task many are afraid of.  The fear of damaging or killing plants seems to be the most common reason I hear of why many gardeners resist pruning.  Knowledge is power, so let’s take a look at some basic perennial pruning techniques that can not only make your garden look better, but can also save you time in the garden.

There are 4 basic reasons to prune perennials:

1. To control height
2. To promote re-blooming
3. To remove tired foliage/promote healthy growth
4. To eliminate the excessive spreading of plants by seed

Controlling height: Many plants we have in our gardens have the tendency to grow taller than we would prefer.  These plants may block our view, flop over or just be out of proportion to their space.  Most often, these are plants that bloom later in the season (summer or fall) so they can often be trimmed in the spring to control their height.  Examples include Yarrow, Monkshood, Asters, Echinacea, Helenum, Lavender, Lobelia, Monarda, Perovskia, garden Pholx, Rudbeckia, Salvia, Vernonia, Tradescantia, Physostegia, Goldenrod, Hibiscus, tall Sedums, Joe Pye Weed, Helianthus and Veronica.  Timing is critical for this process... if you wait too long the plants will not bloom.  During the month of May is when these plants begin to stretch and can be pruned.  Typically, wait until they are 12-16” tall and prune off the top 1/3 of the plant.  The later the plants bloom the later they can be pruned for height control.  Fall Chrysanthemums and Asters (for example) can be pruned up until the 4^th of July and will still bloom.  This pruning will eliminate the need for staking while providing stocky plants and more numerous flowers. 

Promoting re-bloom:  Many perennials have the ability to produce an additional period of blooming if they are trimmed at the appropriate time.  Once the first flowers begin to fade, removing them makes way for and promotes additional flowering.  This is referred to as dead-heading.  Examples of perennials that will re-bloom if dead-headed include; Yarrow, Aster frikartii, Campanula (most), Catmint, Centurea montana, Coreopsis, Dianthus, Delphinium, Dicentra Luxuriant, Echinacea, Echinops, Gallardia, Gaura, Geum, Lavender, Linaria, Lupine, Penstemon, Phlox, Salvia, Scabiosa, Tradescantia and Viola. 

Removing tired foliage:  The downside to many perennials is that once they are finished blooming their foliage becomes tired looking and unattractive.  Many perennials benefit from a severe pruning at this time which promotes a fresh flush of new, healthy foliage.  Perennials that benefit include; Lady’s Mantle, Brunnera, Hollyhocks, Armeria, Rockcress, Goats Beard, Astilbe, Campanula, Coreopsis, Dianthus, Echinacea,  Baby’s Breath, Hellebores, Daylilies, Heuchera, Hibiscus, Hosta, bearded Iris, Red Hot Poker, Daisies, Catmint, Peony, Phlox, Pulmonaria, salvia, Scabiosa, Lamb’s ears, Tradescantia and Veronica. 

Eliminating excessive seeding:  Many perennials produce seed heads than can cause plants to spread either where we don’t want or simply just too much.  Dead-heading these plants saves a lot of gardening time you would spend pulling the excess plants later on.  Perennial plants that can aggressively spread by seed include: Hollyhock, Amsonia, Columbine, Rockcress, Brunnera, Balloon Flower, Rudbeckia, Goldenrod, Thyme, Tradescantia and Violas. 

This is just a brief list of pruning practices that are very worthwhile considering if you want to enhance the performance your perennial gardens.  For those of you who want more information, I suggest “The Well-Tended Perennial Garden” by Tracy DiSabato-Aust.  This is the bible of perennial plant care with all the material you would need to become a perennial pruning perfectionist!

Now go outside and have fun in the dirt!