When to plant peonies

When to plant herbaceous peonies

The RHS gives two planting times for herbaceous peonies, and they depend on how you buy the plant.

Bare-rooted divisions are best planted in late autumn. The RHS says the widest range is available from specialist nurseries, often as bare-rooted divisions in late autumn.

Plants in pots are best planted in late spring. Garden centres sell them in pots ready for planting from late spring to early summer, the RHS says.

When to plant tree peonies

Tree peonies follow a different calendar. The RHS says they are best planted in autumn, but winter or early spring planting is also suitable.

Avoid late spring and summer. The RHS says plants will not establish well in hot, dry conditions.

As with herbaceous peonies, the widest range comes from specialist nurseries, often as bare-rooted divisions in late autumn. A small selection is sold in pots from late spring to early summer.

Site and soil

The RHS plants herbaceous peonies in full sun and fertile soil improved by digging in garden compost. They grow well in a range of soils, including clay, as long as it does not get waterlogged. Each plant needs about a square metre of space without competition from other garden plants, so the RHS spaces them about 1 m apart.

Tree peonies take a sunny or lightly shaded position. The RHS prefers a sheltered spot, so strong winds do not damage the flowers and foliage. They are very hardy, but late frosts can damage the foliage and flower buds, so avoid frost pockets. They prefer neutral, humus-rich, well-drained soil, but tolerate slightly acid or slightly alkaline soil.

Depth: the rule that matters most

For herbaceous peonies, the RHS rule is short: make sure the bright red buds are covered with no more than 2.5 cm of soil, because deep planting reduces flowering. Dig the planting hole the same depth as the root ball or division and twice as wide.

Tree peonies are the opposite. The RHS sets the graft union about 15 cm below soil level. Deep planting encourages the grafted plant to form its own roots.

Dividing and moving peonies

The RHS says peonies are very long lived and steadily make large clumps. It leaves a clump alone until flowering starts to decline, then divides it in autumn.

Cut the clump so each section has at least three dormant growth buds and some roots. Replant the sections with the buds 2.5 cm below soil level. The RHS says divisions should flower two years after dividing.

To move a peony that flowers poorly, the RHS moves it in autumn to a better position, replants it shallower, or both. A moved plant can take a year or two to start flowering again.

Aftercare: water, mulch and winter

Water in to settle the soil, then keep watering regularly through the first summer, especially in dry weather. The RHS says this for both herbaceous and tree peonies. Established tree peonies are deep rooted and, after the first year, should not need routine watering. For herbaceous peonies, the RHS also warns that prolonged drought in spring can cause poor flower bud development, or buds that fail to open. For tree peonies, it says prolonged drought may affect flowering the following season.

Mulch from late autumn to late winter (November to February), in a layer at least 5 cm thick. On herbaceous peonies, avoid covering the centre of the plant, as this could damage the buds. On tree peonies, do not pile mulch against the stems, as they may rot.

When herbaceous peony foliage dies back in autumn, the RHS cuts it at ground level to reduce the risk of infection. Do not worry about ants on the flower buds: the RHS says they do not cause damage.