Herbaceous and woody-stemmed tree peonies Paeonia spp. endure for decades in a garden. Proper growing conditions allow these plants to grow and bloom over the course of 30 to 50 years or more, making them a sound investment. Usually, propagation of peonies centers around root cuttings or divisions, although breeders grow peonies from seed. Three to five years after sowing or transplanting peonies, flowers should be reliably produced each spring.
When sown as seed, at least three years pass before the young peony plant produces its first flower. During the initial growth of a seedling peony, food made in the foliage strengthens the underground tuber roots. Over time, more growth buds develop, and the number of tubers multiply to form a clump with several leaves. As long as seedlings remain healthy, a peony produces its first flower either after three, four or five years, and then continues to bloom regularly each spring.
If a peony growing in a nursery container has reached an age where flowers have already occurred, it will bloom in spring after transplanting. The key is not disturbing or damaging tubers during transplant into the garden. Also, transplanted peonies must not be planted too deeply, as it inhibits flower production. The growing buds or eyes on the tubers of herbaceous peonies or the woody crowns of tree peonies need to be covered with only 2 inches of soil.
Peonies do not require frequent digging and dividing to remain productive. A large clump’s roots may become too entangled after about 10 to 15 years of growth, leading to diminished flower production. After digging up and replanting smaller clumps in late summer or early fall, it takes about two years for the plants to re-establish and again produce lots of flowers. Larger peony roots with three to five eyes begin to produce flowers more quickly compared to younger, smaller root tubers with fewer eyes.
Modern varieties of tree peonies often are grafted onto wild species’ rootstocks. You can see a graft-union with the eye tissues fused atop strong root tissue. Newly planted grafted tree peonies need three years to establish and produce their first flowers, according to Leonard Perry of the University of Vermont Extension.