When and Why You Should Cut Back Perennials and Grasses


We all know that push when fall rolls around — clean, clean, clean before the cold weather forces us inside for the season. Rake up the leaves, sweep off the deck, put the patio furniture away, deadhead the remaining spent flowers, and cut back the perennials. But what if we told you there are some cleanups that can wait until spring? And practices that are actually more beneficial for your garden. Spring cleaning is just around the corner and perhaps you are like us, just itching to get back outside and back in the dirt.

Perennials and ornamental grasses are ideal to cut all the way down to their bases, but which season is ideal? Here are a few tips on how to determine what stays through the winter and what goes.

Wait Till Spring

Some grasses and perennials do not fare well when cut back too late in the season, while others add an interesting dynamic to your landscape design. Listed below are four primary reasons to wait until spring for your pruning.

1. Winter Interest

Just because most perennials and grasses lose their luster, it does not mean they lose all their interest. Some plants have lovely architectural forms that are extra appealing in winter. Yes, leaves drop and colors drain, but take time to appreciate the various heights, forms and seed heads your garden has to offer. These elements look extra beautiful when the Treasure Valley is coated in a blanket of snow. Some perennials are evergreen which are easily enjoyed through the winter because of their foliage, and cutting them back would actually hurt them more than help. Evergreen perennials still benefit from the chlorophyll in their leaves, so cutting back means depleting necessary nutrition to survive the winter months.

2. Protect the Plant

Foliage acts as a natural protection through the winter, and leaving stems means catching wind-blown leaves which adds more insulation. Salvia, a very popular perennial in our zone, has hollow stems. If cut back in the fall, winter moisture can easily seep into the plant’s crown and cause damage or invite disease.

3. Save Time

Some plants are easier and require less energy to clean up in the spring. Take daylilies, for example. Spent flower stems and old leaves are easily removed with a gentle tug. Put away the pruners and hand remove with zero back-breaking work required.

4. Consider Wildlife

Perennials and grasses are natural attractants for wildlife, even in the winter. Birds and squirrels appreciate various seed heads. Black-eyed Susans, sunflowers, coneflowers, and ornamental grasses make for a buffet of options in the dormant months. Grasses also shelter birds and small four-legged animals when the weather turns cold. 

When Fall is Best

While there are benefits to waiting till spring for cleanups, there are still some reasons when fall is best. As a general rule, if you are cutting back in the fall, wait until leaves and stems turn brown — this is a sign the plant is dormant and will not send up any tender, new growth before the first frost.

1. Prevent Overwintering Pests and Diseases

Diseased or infested plants should be cut back and taken care of as soon as possible, and are the best reason for fall cleanups. Do not compost anything affected by pests or diseases — not even suspect plant material — it is best to discard it. Prune foliage down to a few inches above the ground. Make sure to clear out debris from the garden to prevent overwintering rot and pests. Hostas are a good example. Remove their papery, spent leaves as soon as the frost takes them. Dead leaves harbor slug eggs that will hatch and demolish next year’s growth. For every diseased cut you make, clean your pruners to prevent spread to healthy plants.

2. Reduce Chances of Reseeding

Cut down on spring weeding if you do not want to fight self-sowers. Blanket flowers, black-eyed Susans, sunflowers, coneflowers, and columbines are common reseeders. On the other hand, they are also excellent winter feeders for wildlife and add nice structure to the winter landscape. Weigh your options and make the best decision for your schedule, workload, and landscape desire.

3. Unattractive Foliage

Just because dormant perennials and grasses can add nice winter structure, no one wants to look at slimy leaves or fallen and sprawled stems, especially if they topple over onto walkways or lawns. Sometimes something just has to go; make the best judgement on what can stay and what needs to be removed.

4. Plant Division

If you have any spring or summer blooming perennials or overgrown grasses that need division, fall is a great time to do so. Fall gives ample time for plants to set new roots and establish over the winter. Dividing plants in the fall rejuvenates and stimulates growth. September is ideal to cut back perennials and grasses when you divide them. Cutting back allows less transpiration to take place and the plant will lose less moisture while it re-establishes itself.

There are many popular perennials and grasses in the Treasure Valley that can be found in most landscapes. These plants require regular maintenance and upkeep for peak performance. Sometimes it is hard to keep track of what needs pruning versus what does not, what can stay, and what can go. If you have any plant questions regarding pruning and the best season to do so, our garden center staff is always happy and willing to help. Even more readily available, though, check out our resource: 40 of the Treasure Valley’s Most Common Perennials and Grasses for the best time to prune.

40 of the Treasure Valley's Most Common Perennials and Grasses
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By Riley Rehberg

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