In early September a client, who has well-established peonies, wanted to know how late in the year could he transplant his peonies. He wanted to make sure they bloom next year.
Peonies are difficult to transplant; they tend to re-establish slowly. Fall is best time to divide and transplant. Dig under and around plant, cut tubers with sterilized knife and keep 3-5 eyes per section. The client was advised that it probably will be 3-4 years before full bloom is achieved.
Peonies do not need to be divided on a regular basis. In fact, because peonies do not respond well to transplanting, the plants should be divided and replanted only after they become crowded or are in too much shade [2, 3]. This usually is after 10 to 15 years. Crowded or shaded plantings tend to stop blooming. Early fall is (approximately late August through mid-October) is the best time, so that plants can become established before winter.
Plant peonies in a sunny, well-drained site. Do not plant peonies near trees or large shrubs. The shade cast by the trees and shrubs, together with the competition for water and nutrients, will discourage plant growth and flowering. Wet sites promote root rot and frost heaving that may damage and kill peony plants. Peonies should be spaced about 3 to 4 feet apart 
When swollen, red buds are clearly visible, cut sections of the tubers with 3 to 5 eyes each. Divisions with 3 to 5 eyes will reach maturity sooner than smaller divisions. If only one or two eye divisions are used, it may be several years before the plant flowers. 
Dig a hole 12 to 18 inches deep and 12 inches wide. Replace part of the soil in the form of a cone and spread the roots over it. Incorporate compost or peat moss into the soil if more organic matter is needed. Add . cup of 5-10-5 fertilizer to half of the soil and place this soil in the bottom of the hole. Set the roots so that the tips of the eyes are no deeper than 1 inch below the surface. Planting too deeply will inhibit flowering. [3, 4]
Fill the hole with soil and water thoroughly. Water on a regular basis during the first fall and spring after planting. Mulch newly planted peonies with 2 to 3 inches of straw, pine needles, or bark mulch in late fall. Mulching will prevent repeated freezing and thawing of soil that may heave and damage young plants. Remove the mulch as growth resumes in spring. Take care when removing the mulch because the new shoots will be brittle. Do not replace the mulch if a late spring freeze is forecast; peony shoots are cold resistant 
From The Bedford Extension MG Help Desk
Betsy B., Bedford Extension Master Gardener Volunteer; Help Desk Co-Coordinator
PHOTOS: from Bedford Extension Master Gardeners CarolD’s and KathyN’s gardens
All resource links accessed August 21, 2017
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Answers provided herein were based on specific situations and growing conditions.These recommendations may or may not be appropriate for all circumstances.For specific recommendations for your particular situation please contact your local Cooperative Extension Office.
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–A Bedford Area Master Gardeners Association (BAMGA) Publication–