Growing tree peonies

The difference between herbaceous peonies and tree peonies is the stems. Herbaceous peonies have stems that die right back in autumn and leave no trace until they re-emerge in spring. The stems of the tree peony are woody and stay above the ground all year.
 Tree peonies grow into medium sized shrubs and are covered with lots of lush, beautifully divided foliage.

Each stem produces a large, exotic flower usually with a dramatic and very beautiful centre. Some varieties are scented and I have been told that they are good cut flowers. The colours are similar to those of the herbaceous peony; white, pink and red, but many varieties produce true yellow flowers. 

Types of Tree Peonies

Japanese Tree Peonies

Raised in Japan, this type of tree peony grows into an open shrub and produce large flowers that can be double, single or semi-double in form. They have handsome, deeply cut foliage that, in some varieties, turns startling red in autumn. 

Lutea Hybrid Tree Peonies

These tree peonies were raised in France and the USA. They are crosses between two very tough species, and their offspring (p. lutea and p. delavayi). The flowers are truly beautiful, ranging from rich, dark red to bright yellow with a blend of both in between. The varieties we sell tend to have double flowers and form dense, upright shrubs.

All of these peonies are grafted onto herbaceous root stocks, which makes them easy to grow, but certain rules should be followed so that the graft can produce its own roots and establish itself its own independence.

Growing Tree Peonies

Planting

The major planting difference between herbaceous peonies and tree peonies is the depth that they are planted. Plant tree peonies at least 4 inches below the grafting point. In non-grafted the depth needs not be that deep, a depth of 2 inches is sufficient to allow the plant to send suckers out.

Fertilising

A little very well rotted manure can be placed around the dormant plant in winter if the ground is deprived of nutrients, but generally they can be left undisturbed for many years.

Pruning

This is something I have not had to try, but if you have to prune a tree peony because it is too big or unshapely, I would advise caution and taking your time. Pruning should be done in the autumn once the leaves have dropped. Remove the offending stems right down to the base of the plant, but leave one or two longer so the plant can produce some leaves the following year. If the tree peony has happily established itself and no longer requires the root stock this should not be a problem. But if there is any weakness you might find that the plant throws up 'suckers' as a rose does. This is why I would advise to only remove one or two stems the first year, and complete the job the following season. Pruning will also thicken out the bush.

Disease

Peonies can suffer from botritys especially if planted in large groups. This is a fungus and evidence of it can be found at the base of the stem or on the bud. The stem and the bud will be brown and mouldy. In these circumstances, remove the infected area and spray with a fungicide.

Failure to flower

There are three reasons why peonies fail to flower.

1. They have not been planted deeply enough. Remedy - lift the plant in autumn and plant with the buds no more than an inch below the surface of the soil.

2. The plant is too dry during the spring growing season. This can be recognised when the buds are tight and dry.

3. Too much shade. This can also lead to dry roots.

For more information about peonies you could look at The Peony Society website.