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How to successfully divide peonies

How to successfully divide peonies How to successfully divide peonies
By Ralph Purkhiser, Purdue University, Master Gardener

There is an “r” in September. That is important, because my grandmother always told me that one can transplant and divide peonies in any month that has an “r” in its name. What that really means is that it is less stressful to move peonies when the weather is milder or when they are in the dormant state.

There are many reasons one might wish to move peonies. Peonies are long-lived perennial plants and will grow in the same spot for a century or more, but sometimes a move is necessary or is simply desired.

I have a few that I plan to move this month for different reasons. One is a seedling that has grown in a rock garden. It is not likely to survive and bloom on that rocky bank, so I dug it out in the spring and have been holding it in a pot for the summer. It has doubled in size and is ready for a new home.

I also have an Itoh peony that I found at a nursery in June. Note that June does not contain an “r”, so I have also kept that peony in a pot since I purchased it.

Itoh peonies are also known as intersectional peonies. They are the result of crossing an herbaceous peony with a tree peony. The result is a plant that is herbaceous but with stronger stems than the average peony, able to support the larger blooms for which the Itoh peonies are prized.

I also have some plants that I am saving from a construction site. A friend purchased an old homestead and is building a new home. The peonies would be destroyed during the construction process, and I was given permission to dig them.

I also have a special peony that I plan to dig and divide to get more starts. It is a wild Japanese forest peony, which is one of the plants from which our modern garden peonies were developed.

I also have a peony that has not bloomed for a couple of years. That is a sign that the tubers are too deep in the ground. It is near an area where I had to dig a new water line a few years ago and it appears that soil from the excavation likely washed over the peony. Even if there has been no excavation, dust from the air can settle and result in the need to dig and re-set a peony.

While I usually advise leaving the foliage on a plant as long as it is green and still photosynthesizing, I do recommend cutting back herbaceous peonies that are to be dug. Cut the stems to about four inches in height. During the digging process, you do not want to pull on the stems, as they break off easily.

When digging a peony, like most plants, one wants to get as much of the root ball as possible. For this reason, I advise using a digging fork instead of a shovel or spade. Shovels would cut through the fibrous roots, but using a fork allows one to break up the soil around the roots and then lift the plant.

Start digging several inches back from the stems, digging from different sides and lifting slowly. If the plant does not seem to be lifting, move back a few more inches and try again. Breaking off some of the roots is inevitable, but you want to keep the damage to a minimum.

When you have loosened the root ball, lift the plant and place it on a level surface, such as a tarp or piece of cardboard. Check the roots for damage and prune off any that do not look healthy.

If you plan to divide the plant, make sure that each division has at least one of the swollen tubers and that each tuber has at least one “eye.” Use a sharp knife to make the cuts and tease the roots apart gently.

When planting in the new locations, select spots that receive at least six hours of sun each day. The exception is the forest peony, which will do fine in shady locations.

Dig a hole at least twice the size of the root ball. Remember that the roots do not want to be too deep. The main tuber should be within two inches of the surface.

You may want to mix the soil with a little compost but do not do too much amending. You want the roots to grow into the surrounding soil, not stay in the rich vase created by amending the soil.

I do recommend using a root-stimulating fertilizer in the soil, and I like to water them in with Quick Start or some other type of water-soluble root stimulator.

Wait until the ground freezes to apply a layer of mulch that will prevent the roots from heaving during the freeze-thaw cycles of winter. Your plant will awaken early in the spring, and you may have blooms next May.