There is a common misconception that you can’t divide peonies. I have mentioned peonies many times before but as we are coming into spring it is worth dispelling the myth that dividing peonies is a bad idea or that it will prevent flowering. Herbaceous, garden peonies are longlived and do not need regular division, unlike so many garden plants. They can be left for years, even decades, to get on with life and I am sure we all know old clumps in gardens where the owners do very little to encourage them. It is true that, in many respects, time is the best fertiliser for peonies.
But they certainly can be divided. The belief that they can’t may be down to the fact that they don’t need it, perhaps people were mean and didn’t want to give them away – or didn’t want the work (peonies have large, thick roots) or perhaps its stems from old stories about woodpeckers pecking out the eyes of hapless people that dug the roots, I am sure this is because physicians valued the roots and didn’t want everyone harvesting the roots for themselves. Incidentally, the medicinal use of peonies is well established and Paeon was physician of the Greek Gods and both Ares and Hades were healed with peony root.
Another reason for the story about not dividing peonies is almost certainly because the planting depth of peonies is very important and if they are planted too deeply the shoots will grow but they will not bloom and this can continue for many years.
But they obviously can be divided because the plants have to be lifted and split to propagate them for sale. You can buy peonies either as potted plants (they are usually grown in a field, lifted, split and potted and sold the following summer) or as bare roots. They are not bulbs and must not be left out of the ground long or they will dry out.
You can divide them whenever they are dormant, from November to March. But the best time is in early March, just as the thick, red shoots are starting to grow. Division will inevitably cause serious damage to the thick, pungently scented roots and they will heal, rather than rot, if cut in spring. The roots are thick and woody so, after lifting and knocking off some soil, it is best to get in with a knife and cut off sections, making sure each has several shoots attached. In theory you can cut the roots into sections with just one shoot but these will take several years to make a decent clump so, unless you need lots of plants, it is best just to divide a mature clump into three or five.
Before replanting, prepare the site well with lots of garden compost or well rotted manure – after all the peony will be living there for many years. Most importantly, plant so that the crown of the plant, where the shoots grow from the root, is 2.5cm below the soil surface – no deeper. Deep planting is the most common reason why newly planted peonies do not flower – apart from planting small pieces with small shoots. I bought some in bags from a four-letter supermarket in autumn. They were (if correctly named) unusual varieties and (it being autumn) looked fresh. So I bought them and potted them and will plant in spring. I won’t expect flowers this year but it is not impossible.
Another reason why peonies don’t flower (and there are others) is that they are being shaded by a shrub or tree that has grown. Here dividing and moving should get the peony flowering again if planted in sun. But it may take several years. There are other reasons why peonies don’t flower but that wasn’t the question and I have been sidetracked quite enough!