I have a very old, 15 years, white blossom tree peony that has become very leggy. It is now about 4 feet tall. This year it has 5 buds, the most ever. The graft peony at the bottom is very vigorous and gives me one or two blooms also but of a different colour. I would like to trim the tree peony back. When do I do this? And the stems are very woody…will I kill it?? Photo too big to send but could do so later if needed
Thank you for contacting Toronto Master Gardeners regarding the pruning of your 15 year old white tree peony. Tree peonies (Paeonia suffruticosa) are long-lived deciduous woody shrubs native to China. There are many named cultivars of the original tree peony but they generally share similar cultural needs. Tree peonies grow best in full sun to part shade, and in neutral to slightly alkaline soil with good drainage.
You mentioned issues with size, sparse blooming and non-white blossoms on a graft off-shoot. Since your peony produced 5 flowers for the first time, one wonders what, if anything, had been done differently during the past growing season. Without a description of its growing environment, it is difficult to be precise about the specific needs of your plant. Lack of blooming can result from several things, inadequate light, watering issues, pH of water and lack of organic matter, and suckering (the vigorous growing shoot with non-white flowers). Too much nitrogen can result in the growth of leaves at the expense of flowers. Over the years, increasing shade also can reduce the number of flowers produced.
In general, pruning in spring should be confined to removing dead or damaged branches and suckers. Use appropriate sized by-pass pruner or lopper which are disinfected after each cut to prevent potential spread of disease. Pruning should be done just above an outward facing bud. Remove spent blooms after flowering. Careful shaping of a leggy plant is done in the spring and gradually over several years. This may result in a loss of a few of the year’s flowers. While pruning will stimulate growth, peonies do grow slowly.
For more information, please see:
http://canadianpeonysociety.blogspot.com/p/planting-instructions.html
https://www.torontomastergardeners.ca/askagardener/tree-peony-not-blooming/
Wishing you success in pruning your peony.