Almost everyone loves peonies. Their large flowers are a sight to behold, and their low-maintenance form makes them easy to care for. However, providing them with the proper care will help them remain healthy and productive for decades.
While herbaceous peonies don’t require much maintenance to remain healthy, tree peonies form woody growth that responds well to pruning. Carefully removing unwanted growth can prevent stems from becoming leggy and encourage healthy new growth. In this article, I’ll cover how and when to prune peonies for the best results.
Herbaceous vs. Tree Peonies
Identify your peony type before pruning for best results.
Before you begin pruning, make sure you know which type of peony you’re dealing with. There are two main types of peonies: herbaceous and tree.
Herbaceous peonies are what many gardeners imagine when they think of these beautiful flowers. They are perennial herbaceous plants that grow new stems each spring. The stems and leaves fade during the summer and die back each winter. They then send up new growth the following spring.
Tree peonies are perennials that grow as deciduous shrubs. Although they drop their leaves in the fall, their woody stems remain year-round. Mature plants can grow up to six feet tall, making them much larger than their herbaceous counterparts.
Although you can cut back herbaceous peonies’ stems in the fall, they don’t require true pruning. Since tree peonies produce woody stems, they can benefit from pruning. Pruning isn’t necessary, but it can help improve plant shape and health. Follow these steps to prune tree peonies properly.
Wait Until They Are Mature
For young tree peonies, let them grow undisturbed.
When tree peonies are young, they don’t require pruning. Removing growth on small specimens can stress them and stunt their growth. Therefore, leaving them alone for the first two to three years is best.
Choose the Correct Time of the Year
Trim in early spring or fall for optimal growth.
After determining that your plant is large enough to tolerate pruning, wait until the right time of year. The early spring is the best time to prune peonies in most locations. However, you can also trim in winter if you live in a warm climate.
Your goal is to prune early enough that they haven’t started growing but late enough that they won’t experience cold damage after pruning. Keep an eye on the buds and look for the moment they begin to swell. This indicates it’s a good time to cut back. Although spring is a good time, you should be aware you’ll be removing some of this year’s flower buds.
You can also prune tree peonies in the fall after they have gone dormant. If you opt for this option, be aware an early cold snap can damage recently trimmed specimens. Therefore, try to prune shortly after they enter dormancy.
Avoid pruning in the late spring and summer when they are actively growing. Cutting back during this time can cause the plant to produce new growth that may not be strong enough to survive the winter. It also leaves them more susceptible to disease and insect pests.
Use sharp, sanitized tools for clean cuts.
Starting with the proper tools is a key part of proper pruning. They’ll make your job easier and help keep your plant healthy.
A pruning saw and a pair of hand held pruning shears are enough to get the job done. Make sure the blades of both tools are extremely sharp. Sharp tools lead to clean cuts and, therefore, speed healing.
You should also sanitize the tools before using them. You can dip the blades of the tools in a 1:10 solution of bleach to water or 70% isopropyl alcohol. This will ensure you don’t spread diseases between plants.
Remove Dead Wood
Remove dead branches close to live buds for healthy growth.
The first step in pruning is removing any dead branches and stems. Since you’ll be pruning when the peonies are dormant, it can be difficult to determine which parts of the plant are dead. That’s where the buds come in.
If you remember from above, you should wait until the buds start swelling before you begin pruning. Swollen buds indicate live growth and are a helpful indicator for identifying dead wood. If you see buds that are small, the wood they are attached to is dead.
Other signs of dead wood include brittle and/or shrunken branches. Living branches will bend, while dead branches will snap.
Once you determine which section of the branches are dead, it’s time to remove them. Aim to remove them close to the next living bud. For example, if an entire side branch is dead, you can cut it a quarter of an inch away from where it connects to the main stem. If the top few inches of a stem are dead, cut the stem a quarter of an inch above the highest living bud.
You can use either shears or a saw to cut the branches. No matter which tool you use, aim for as clean of a cut as possible. Rather than cutting straight across the branch, cut at a 45° angle with the cut sloping away from the nearest bud. This will allow water to drain off the branch, preventing disease and speeding healing.
Prune Slender Growth
Remove slender stems to help the plant focus on growth.
Sometimes, tree varieties will begin producing slender, spindly stems that aren’t likely to produce buds and flowers. Removing these stems will allow the plant to focus its energy on healthier branches.
Since these stems are skinny, you can use shears to remove them. Cut the stems a quarter of an inch away from where they connect to the rest of the plant. If they are sprouting directly from the base of the plant, you can cut them flush with the ground.
Remove Crossing Branches
Eliminate crossing branches to prevent damage and disease.
Like most woody species, tree peonies can develop branches that cross and rub against each other. This rubbing can remove the bark and leave the stem susceptible to disease and insects. Therefore, it’s a good idea to remove any stems that cross each other.
The amount of branch to remove depends on how the plant is growing. You can remove an entire stem where it connects to the main branch or prune off the edge of a branch that’s rubbing against another.
As I explained above, you should always aim for a clean, straight cut. If you’re removing only part of the branch, cut it a quarter of an inch above a living bud.
Prune for Shape
For a bushier shape, trim tops just above buds.
Although there’s no need to alter the shape of your tree peony, sometimes they get taller or more leggy than we’d like. When this happens, you can remove the tops of the plant’s branches to alter the plant’s size and shape. Before you begin cutting back for size, it’s important to make sure you’re not removing too much growth at once. Never remove more than one-third of the woody growth per year.
If you want to encourage a bushier shape, you can remove the top quarter of each stem. Cut just above a bud, making sure to angle the cut downward away from the bud. New growth will emerge from the bud and lead to a full, bushy shape.
If you want to remove more of the plant, plan to prune your peonies over multiple years. Although this may seem like a slow process, it will prevent the peony from becoming weak.
