Shrub peonies in pots: how to grow them successfully?

Why don't shrub peonies like to be grown in pots?

Shrubby peonies are among those plants seldom grown in pots. This is for several reasons.

1. They develop a solid, deep root system, which requires space and a large volume of soil.
2. They often have a silhouette as wide as tall, with a flared or spreading habit that can reach nearly 3 metres.
3. They hate being moved once mature.
4. They have very slow growth and produce few branches, initially putting energy into developing their root system. You generally need to wait at least 3 to 4 years for the plant to thicken up and for flowering to become truly generous.

If you do not have a garden but are determined to grow this plant on a balcony, a small terrace or an inner courtyard, you will need to follow certain recommendations.

Large in size, shrubby peonies are not well suited to cultivation in pots

Choosing the right varieties

To increase chances of success when growing tree peonies in pots, choose varieties with the smallest habit, particularly in width.

These include:

• Paeonia suffruticosa ‘Wu Long Peng Sheng’, with its lovely violet-pink flowers;
• Paeonia suffruticosa ‘Xue Ta’, with delicate cream-white flowering;
• Paeonia suffruticosa ‘Cai Hui’, with vivid pink flowers;
• Paeonia suffruticosa ‘Ri Yue Jin’, which blooms in intense red;
• Paeonia (x) lutea ‘Alice Harding’, with sunny lemon-yellow flowering.

Barely exceeding 1 metre in spread, they are better suited to cultivation in containers.

Provide a suitable container

To successfully plant a tree peony in a pot, start by choosing an appropriate container. Nous l’avons dit, cette plante n’apprécie pas d’être déplacée : it is donc essential to choose its final pot from the outset.

Choose fairly wide models, measuring at least 1 metre to 1.50 metres across. In terms of depth, you will also need to allow space: allow at least 1 metre, or more. Ideally opt for a large planting container, which will remain in place.

Make sure, however, that the base is not watertight, so that excess irrigation or rainwater can drain away without pooling.

A large pot will be necessary for growing a tree peony

Find the right exposure

Peonies do not like being moved to a different environment. You will therefore need to choose a definite location for them, particularly as container size will make them difficult to move.

These plants prefer semi-shade, or possibly gentle sun, but never scorching. They should receive at least 4 to 6 hours of sun per day. Even though they are hardy, they cannot tolerate cold winds, which can also affect their flowering, as the flower buds are sensitive to late frosts.

Sun exposure is worth considering

Best practices when planting

Planting is best done in autumn.

For your tree peony, choose a well-draining substrate rich in organic matter. You can mix garden soil that is not too clayey with river sand or clay pebbles, and well-rotted household compost or mature manure. You can also opt for a ready-made potting compost, such as the potting compost for roses or the potting compost for planters and pots.

1. Place a 5 cm layer of drainage material at the bottom of the container. Use gravel or clay pebbles.
2. Fill halfway with substrate, then position your tree peony in the centre. Add more substrate until the graft union (the swollen union at the base of the plant) is buried to about 5 cm.
3. Firm the substrate with your fingers to remove air pockets.
4. Water generously.
5. Apply an organic mulch around the base of the plant, such as hay, straw or wood chips. This helps keep soil cool by reducing evaporation. You can also choose to plant ferns or Hostas, which will dress the base.

Bury the graft union 5 cm below ground

How to care for a tree peony in a pot

Tree peony requires some care to develop well and to reward you with a fine display of flowers.

First, it prefers moist soil, that is, soil that never completely dries out. As soon as soil is dry at surface, remember to water. Prefer rainwater, which is less hard than mains water, or use a pH‑balancing product. Watering should be regular from spring, and frequent in summer, especially during hot spells. Take care not to wet the foliage when watering.

Water more generously in a pot, but avoid wetting the foliage

Each year at the end of winter, add compost, manure, horn meal or fertiliser for flowering plants (usually rich in potash). Products in stick or granule form should be mixed into the soil. They provide slow‑release, long‑lasting feeding. Liquid fertilisers, for their part, are diluted in water and give a short‑lived boost.

Finally, be patient if you want to enjoy a good flowering. For pruning, simply remove spent flowers as they fade. Once the plant is well established, remove only weak or crossing branches. Always remember to disinfect cutting tools after pruning to reduce risk of spreading disease.

Tree peony is not very susceptible to disease: it is mainly vulnerable to excess water.