Answer: Peonies can develop disease problems, but this late in the summer, I suspect the yellowing and browning of leaves is a normal reaction to cooler temperatures. If your plants performed well all summer, they're probably just fine. When frost kills the tops of the plants back, remove the debris from the garden, then mulch over the roots of your plants. Healthy new growth should sprout in the spring. If your plants seem overcrowded or didn't bloom well this year, they may benefit from division. Peony plants can be divided to start new beds in late summer or fall. However, you'll want to be as gentle as possible with the peony plants; they are sensitive and may take a couple of years to bloom after dividing. Unlike many perennials, peonies can go for many years without needing dividing.
To divide peonies, separate a portion of the peony clump by inserting a spade shovel and making a vertical cut into the root ball. Dig up this portion, and replan tin a carefully prepared bed. (Fill in the hole left next to the parent plant with rich soil.) Or you can dig up the entire peony plant and prune off a section of the root ball. Then replant both sections in prepared beds, taking care to plant the crowns no deeper than one and a half to two inches below the soil surface.
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