Herbaceous Peonies

Many people are under the impression that peonies are difficult plants to grow. It is difficult to say where this myth originated from but it may go some way to explaining why peonies are less popular in the United Kingdom than they are in the USA. Peonies are actually very easy to grow; once established they can tolerate drought and suffer from very few diseases.

The most commonly cultivated herbaceous peonies, that is varieties of Paeonia officinalis and P. lactiflora, are very tough plants. It is true that it may take a couple of years for a divided plant to resume normal flowering, but surely this applies to most herbaceous plants when they are propagated by division?

Unfortunately very few garden centres in the UK sell high quality peonies. They are considered to be just another plant for the herbaceous border and are usually sourced from wholesalers in Holland. In the USA growers would not consider selling a peony unless it had at least three to four buds on a division. Smaller divisions are obviously more profitable and it is common to see plants for sale in this country that have only two to three buds. Such ruthless treatment drastically reduces the capacity of the plant to recover from its ordeal.

The best quality plants come from a specialist nursery, such as Kelways Ltd in Somerset or Claire Austin Hardy Plants Ltd. in Shropshire. These peonies, which are usually supplied as bare roots, are likely to flower during their first season and will reach maturity much quicker than containerised plants. Bridgemere Nurseries in Cheshire used to be a good source of containerised peonies, but they have recently closed down their wholesale department and it remains to be seen whether they will offer the same range of plants in the future. It is not really viable to import plants from the USA unless you are intending to spend more than £200 on peonies. The best source for species peonies is Phedar Nursery, near Manchester.

The most important thing to remember when you are planting a herbaceous peony is to ensure that the young buds are approximately 5cm (2") below the surface of the soil. If you fail to do this it is unlikely that the plant will flower well. If there is any doubt, dig the plant up in the autumn and replant it at the correct depth.

Tree Peonies

Tree peonies are often badly planted and this produces a sickly bush with one or two weak branches. Most Japanese tree peonies are grafted and it is absolutely essential that this graft union, between the scion and the rootstock, is planted below the surface of the soil. The ideal depth is approximately 15cm (6"). If the peony is planted correctly the scion will produce its own roots and will become a vigorous multi-stemmed plant. The rootstock eventually rots away.

The Chinese have, until recently, propagated their tree peonies by division. Divided plants tend to be more vigorous than grafted plants, but in recent years the Chinese have also adopted grafting as a means of mass propagation.

Pests and Diseases

Peonies are fortunate in suffering from very few diseases. The most serious disease is Peony Wilt, which is caused by a fungal pathogen called Botrytis paeoniae This disease rarely causes problems in a dry spring but can spread like wildfire during a wet one. Botrytis is potentially a far more serious disease in the UK than it is in America, mainly the result of our wetter 'Atlantic' climate. Peony Wilt causes the tissues of the plant to turn black and, if it is left untreated, the disease can easily kill the plant. The best way to control it is to use a systemic fungicide. All infected material should be destroyed to prevent the disease spreading. Prevention is always better than cure and this can be achieved by spraying the peonies when the buds start to burst in the spring and once or twice during the growing season.

Organic gardeners can achieve a great degree of control by removing and destroying any infected material. Vigilance is absolutely essential however, as the disease can spread very quickly in wet weather.

We have had a particularly wet spring this year. Potted plants, in peat-based composts, are particularly vulnerable to crown rot in these conditions. If your peonies are affected the compost should be removed from the infected area, allowing air to reach the damaged tissues. Infected material can removed with a sharp knife, while the healthy parts of the plant can be liberally dusted with green sulphur.

Storing Peonies for Transplantation

The best way to transport peonies from one location to another is to dig them up in the autumn and divide the crown. The divisions can them be shipped to your new home and planted. Unfortunately this is not always possible, we cannot always plan when we are going to move house.

It is possible to dig peonies up at any time of the year but the chances of success are slim if this is done during the period when they are actively growing. The worst time of the year to move them is during the months of May and August. If the plants have to be moved at this time try to keep as much of the root ball together as possible, even if this means taking a lot of soil with you. Water the plants regularly after replanting and water every day if the weather is particularly hot.

The best way to move mature plants is to plan your move several months in advance. Peonies grow remarkably well in rectangular plastic baskets, which are widely used in wholesale horticulture. The best ones are made out of black plastic and measure approximately 40 x 60 x 25cm. Both the sides and base are ventilated and they allow the peony to develop a normal root system. These baskets may not be available for sale, but if you ask your local garden centre they may have some that they are willing to sell to you. Herbaceous peonies do not like being grown in pots, but if you have no choice use a loam based compost (John Innes No. 2 or 3 is best) and the largest pot that you can find. Keep containerised peonies well watered and plant in the autumn when you have moved to your new home. All containerised peonies will need regular watering during the summer.

Further information about growing peonies can be found in 'The Gardener's Guide to Growing Peonies', published by David & Charles Ltd. in the British Isles and Timber Press in the USA.

Labelling

One of the biggest problems that gardeners have is in identifying a peony that has lost its label. Peonies can easily last for 50 years without being divided and during this time it is highly likely that the plant will lose its identification label.

To prevent this happening in the future we advise gardeners to:

• Use a long lasting aluminium tag to mark the plant on the ground
• Bury a plastic label among the roots
• Establish a grid for your garden and mark the position of the plants within the grid

This page ©2004 Dr Martin Page.