Here is a picture of my peony. The flowers were small, then they stopped growing bigger . This happened last year and this year. It is in full sun and sheep manure was added and it was watered and fertilized .
Thank you for contacting the Toronto Master Gardeners concerning your peony.
The non-flowering of your Peony could be one of two potential problems or both could be related, see below.
Firstly, peonies do not like to be planted too deeply. If you have added layers of manure around it for the last few years, the root system is getting deeper and deeper. The solution here is to dig it up and raise its level in the soil when replanting.
Secondly, overfeeding will cause the plant to grow vegetatively rather than producing flowers – the buds may be there but it won’t bloom. The solution here is to stop adding manure and fertilizer for a couple of years.
The Laidback Gardener has a great blog that discusses 9 Reasons Peonies Don’t Bloom
Hope this helps.