This is one of a new series of posts based on real questions I have been asked. Feel free to add to the answers or include your ideas and experiences.
This question was about a peony which was 10 years old and had lots of foliage but no flowers. It was in partial shade with Japanese anemones and asters all thriving around it. It was taken from a relations’ peony which had red flowers.
The peony was probably P. officinalis ‘Rubra Plena’ (now P. x festiva ‘Rubra Plena’). It is a very common peony in old gardens because it is strong and, like most, longlived.
There are two main reasons why peonies fail to bloom and both are problems that can occur immediately, so are due to poor choices when planting or can get worse with time, so develop even though things are fine at first.
Peonies, despite what is often said, move perfectly well, as long as they are not out of the ground too long. But small pieces, with small roots and only a few, small buds, will need some time to mature and increase in strength before they bloom. Small buds produce thin shoots which will not have flower buds, just leaves. Not all the stems on a peony plant will be strong enough to bloom. This is normal.
Peonies need a sunny site to flower well. They will survive and grow in some shade but will not flower as well. Light shade can help flowers last a little longer – peony flowers, especially the singles, are notorious for not lasting long. But too much shade not only weakens the plants so they do not bloom well, but it can cause the stems to stretch so the stems have less ability to stand up when the flowers are fully open, a common issue anyway with the doubles. If surrounding plants get larger over the years, peonies, because they live for years, can get more shaded, and this reduces flowering. Unlike many other perennials, peonies do not need regular division to keep them blooming.
The other problem is if the roots are planted too deeply. The top of the crown, where the shoots emerge from the roots, should be no more than 2cm (1inch) below the soil surface. If they are deeper then the plants produce thin stems and not strong, flowering shoots. The problem can be immediate, if they are initially planted too deeply or it can get worse over the years if the plants are heavily mulched. It may be possible to scrape away some of the surface soil or it may be easier to dig up the plant and replant at the right depth. This should be done when the plant is dormant, between October and late February or early March, though early spring is often easiest.
Remember that, after remedial action is taken, it can take a year or more for the plants to recover and improve.
Another question I often get is whether peonies can be grown in pots – after all they are often bought in pots! But these potted plants will have been grown ‘in the field’ and potted the previous season for sale in pots. Peonies are heavy feeders and have a big, thick, root system and they are not ideal for pots. If you want to try then use a large pot and always use a loam-based compost such as John Innes No 3. They will need constant watering and will benefit from regular liquid feeding and I am not sure that the rewards repay all the effort, despite my love of peonies. They are far better planted in the ground.