Common Mistakes Everyone Makes When Pruning Peonies

Common peonies (Paeonia hybrids) make for an excellent part of any garden thanks to their large, often fragrant flowers that come in a variety of colors. Sometimes called the "King of Flowers," they have been a status symbol since the people of China domesticated wild peonies for medicinal use over 2,000 years ago. If you're interested in successfully growing your own peonies, you'll want to be careful to avoid common pruning mistakes while maintaining these herbaceous perennials. To start, there are multiple ways to prune your peony plants depending on the season.

During the active growing season in spring and summer, focus on light maintenance pruning. This includes deadheading, or removing older, spent flowers; disbudding, or removing younger buds that take away from the main buds' growth; and thinning, or increasing the space between dense stems. Thinning is great for shaping a plant and letting more light and air circulate, but you'll want to avoid taking off more than ⅓ of the stems at a time when your peonies are about a quarter of their mature size. Your peonies need enough foliage to grow and store energy for blooming. As the growing season ends and the plants begin to die back due to freezing temperatures, usually around October or November, you'll want to do a more serious prune. 

Trim the plants near ground level to a height of around one or two inches and be careful not to injure the crown, which can be found at or below the soil level in the center of the plant. Damaging the crown will hinder the plant's ability to produce flower buds for the next spring. Peonies are tubers, and you can divide a section of its crown with a few premature buds and attached tubers to grow more (though recently divided parts won't produce blooms for a time). Just don't make the mistake of burying your herbaceous peonies too deep. Going more than an inch or two beneath the surface means they may produce leaves but will never bloom.

Peonies can become infested with pests or contract a number of diseases that would require you to prune portions or entire plants during the growing season. These include bacterial blight, foliage becoming coated with a fungal powdery mildew, or root rot that entirely stunts growth due to a lack of oxygen (often as a result of overwatering). However, you also need to be aware of diseases that mean you would be mistaken to replant peonies in that same area. These include Verticillium wilt that occurs without visible damage to the crown, or a white mold infection that causes stem discoloration and rot. 

If you happen to be pruning diseased plants, another common mistake is not properly sanitizing your shears with alcohol, bleach, or household disinfectants between cuts, which may result in spreading the infection. There are also a lot of mistakes one can make when trying to get rid of diseased peony debris. It is possible to kill diseased material and other nuisances like weed seeds if you have a composter that reaches at least 148 degrees Fahrenheit, but you generally want to avoid tossing anything diseased into your backyard compost pile. 

Disease-causing fungi or bacteria that survives might spread, so it's best to find other avenues for your discarded peony trimmings. For example, with a large enough garden, you can bury the debris far away and let it naturally decay for at least a year, and then rotate in a different type of plant thereafter. In most cases, though, it's best to just bag the diseased pieces and throw them away.

If you want strong peonies to prune in your garden, you'll want to give them the best shot at life from the jump. There are multiple varieties of peonies that might affect the specifics, but the common herbaceous garden peony will naturally grow best in mountainous regions falling in USDA Hardiness Zones 3 through 8. They thrive in anywhere from partial shade to full sun (so long as they receive two hours or more of direct sunlight every day), and should be planted in acidic soil with high organic matter and good drainage. September is the best month to plant or transplant your peonies, ideally incorporating fertilizer with phosphorus-rich materials like bonemeal if you need to fix an acidity imbalance in the soil.

A single peony plant might brighten your garden for decades with proper care, which includes employing the right pruning techniques using tools such as bypass pruning shears (like this Fiskars pair available on Amazon) that can cleanly trim thick stems. However, unless you find signs of disease in your garden, don't be afraid to leave your dead plant tops full over the winter. Perennial flowers that will never leave your garden like peonies provide food for birds and shelter for insects when the weather gets cold, so leaving a more natural landscape over the winter can be beneficial to the local ecosystem.