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In that case, I would dig it up and divide it. The mother plant will come back as good as new.
Division
Peonies should be divided in the autumn
Remove the foliage and lift the clump carefully
Gently remove or wash off the soil to expose the roots and growth buds
Using a sharp knife, remove sections of the crown with at least three dormant growth buds each and roots attached
Replant with the buds 5cm (2in) below ground level
Peony: herbaceous / Royal Horticultural Society
Division
Peonies should be divided in the autumn
Remove the foliage and lift the clump carefully
Gently remove or wash off the soil to expose the roots and growth buds
Using a sharp knife, remove sections of the crown with at least three dormant growth buds each and roots attached
Replant with the buds 5cm (2in) below ground level
Peony: herbaceous / Royal Horticultural Society
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