When to Cut Back Peonies

One of the most frequently asked questions when it comes to garden maintenance is how to control tall perennials with large, heavy flower heads. However, pruning peonies is just as important as proper peony care.

Why, when and how to prune your peonies to get the most out of these gardens.

Is it necessary to prune peonies?

Aside from aesthetic considerations, the main reason for pruning peonies is the health of the plant. Peony diseases can be controlled by removing diseased plants during the growing season and cutting back the entire plant after the end of the growing season in fall.

Dead Peony

Pruning peonies differs from pruning deadheads, which is the removal of spent flowers after they bloom. If the flowers remain on the plant, they will produce seeds rather than store all of the plant's energy in the roots, ensuring the plant's health and next year's flowering. It does not matter how much you trim the flower stalks. For a clean look, though, it's best to cut them below the foliage so they don't stand out.

Deadheading also lengthens the flowering time of Itoh peonies, which bloom later than garden peonies, but are also deadheading.

Remove Flower Buds

Newly planted peonies benefit from removing flower buds completely before they bloom in the first spring. Not every gardener eager to see peonies bloom is willing to make that sacrifice. But preventing peonies from blooming in the first year after planting helps the plant become established, and the reward is abundant flowering in subsequent years.

Peony Plant Removal

Pruning peonies during the growing season is optional. This should be done as needed to prevent the spread of disease. On the other hand, it is always important to prune peonies in the fall.

Pruning to Control the Disease

Two common fungal diseases of peonies are peony leaf spot and powdery mildew. Fungal spores overwinter in dead leaves and infected plant debris. Good sanitation, which includes cutting off affected plant parts during the growing season and disposing of plant material in the trash, helps control the spread of the disease.

Peony leaf spot is caused by a fungus called Cladosporium paeoniae. Because of the typical bright purple or brown spots or spots on the upper surface of the leaves, it is also called scab or red spot. As the season progresses, the larger leaves may become distorted, and reddish-brown streaks may appear on the stems.

Another fungal disease affecting peonies is powdery mildew. Unless the chalky residue on the leaves of powdery mildew is severe, it is more of a disease of the plant. However, to keep it under control, cut back infected leaves and collect any infected leaves that have fallen to the ground to prevent reinfection.

When cutting off diseased leaves, keep a bucket of one part chlorine bleach and nine parts water at the ready to sanitize your cuttings. Dip them into the mixture and dry them with a clean cloth so you don't spread the fungus spores from plant to plant.

A lack of good air circulation along with a build-up of moisture can exacerbate the spread of fungal diseases in peonies. If your peonies have healthy but very bushy foliage, it's a good idea to thin the plants a bit to let in more air and sunlight.

Fall Cleaning

In the fall, cut back the peonies but wait until the plants are dead or completely yellow after a hard frost. If you prune your peonies too early, you reduce the amount of time the plants have to absorb sunlight to build up the plant's energy reserves. 

Advice

Unlike garden peonies, tree peonies, which are woody perennials, require very little pruning other than trimming and trimming any dead branches.

How to Prune Peonies

1. Cut stems at or near ground level after a hard frost.

2. Thoroughly remove all plant debris and dead plants regardless of whether the peonies are diseased or not. Dead plants may contain fungal spores that are not visible to the human eye. If the plants are sick, dispose of them safely in the trash. Do not compost it under any circumstances.