Paeonia rockii, Rock's tree peony — upright deciduous (Paeoniaceae) (image 1 of 10)

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Paeonia, Genus, rockii, Species,

Genus & species

Rock's tree peony

Paeoniaceae

Qinling mountains of central China, in Gansu, Shaanxi, Henan, and Hubei

Attracts Pollinators Deer Resistant Drought Tolerant Fragrant (moderate)

SunFull Sun – Part Shade

WaterMedium · drought-tolerant

HardinessZones 4–8

Overview

Paeonia rockii is a deciduous shrub with persistent woody stems, reaching 4-7 feet (1.2-2.1 m) tall and 4-6 feet (1.2-1.8 m) wide over 10-15 years, occasionally to 10 feet (3 m) in old plantings. Unlike herbaceous peonies, the stems do not die back in winter; they hold their height and carry buds through the cold months. Leaves are bipinnate, 8-14 inches (20-35 cm) long, divided into 15 or more lance-shaped leaflets that are blue-green above and paler beneath. Flowers are 6-10 inches (15-25 cm) across, single to semi-double, with white to pale pink crinkled petals each marked at the base by a deep maroon-purple flare, so the centre of the open flower shows a ring of dark blotches around a boss of yellow stamens on purple filaments. Scent is sweet and carries several feet on still mornings. Seed pods split in late summer to release large black seeds. Flowering lasts only 7-14 days, and plants take 4-6 years from a grafted young plant to reach full flowering size. Wet springs bring botrytis blight, which blackens buds before they open. It is hardy in USDA zones 4-8 but flower buds are damaged by late frosts below 28F (-2C).

Native Range

Paeonia rockii is native to central China, in the Qinling and adjacent mountain ranges of southern Gansu, Shaanxi, Henan, and Hubei, growing in open scrub and forest margins at 3,600-9,200 feet (1,100-2,800 m). Wild populations are small and fragmented, and the plant is listed as threatened in China. Nearly all garden plants trace to cultivated stock rather than wild collection, with the Gansu group of cultivars developed around Lanzhou over several centuries.

Suggested Uses

Grown as a specimen shrub in mixed borders and courtyards in USDA zones 4-8, spaced 5-6 feet (1.5-1.8 m) from neighbouring shrubs to allow the framework to develop. It is planted with early bulbs and hostas that occupy the ground beneath the open framework in spring and summer. Cut stems last 3-5 days in water and are used for short-lived indoor arrangements.

How to Identify

Woody stems that persist above ground through winter separate P. rockii and other tree peonies from the herbaceous peonies, whose stems die to the ground each autumn. The dark maroon-purple basal flare on every petal, contrasting with white to pale pink petal blades, distinguishes P. rockii from P. suffruticosa cultivars, in which the flare is absent or restricted to a small area. Leaves are bipinnate with 15 or more leaflets, more finely divided than the 9-leaflet leaves typical of P. suffruticosa. Flowers reach 6-10 inches (15-25 cm) across, roughly twice the diameter of most herbaceous peony blooms.

Appearance

Size & Dimensions

Height4' - 7'

Width/Spread4' - 6'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~2 weeks

Flowers: April–May

Spring

Flowering falls in mid to late spring, usually from late April to mid May, about a week before herbaceous peonies open in the same garden. The display lasts 7-14 days, with individual flowers open for 3-5 days and shortened to 2-3 days by heat above 80F (27C) or heavy rain. Mature shrubs carry 20-50 flowers in a season; young grafted plants produce 1-5 for their first few years. Afternoon shade extends the life of each open flower by 1-2 days.

Detailed Descriptions

Flower Description

White to pale pink with a maroon-purple basal flare

Foliage Description

Blue-green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-6 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.5 - 7.5 (Neutral to alkaline)

3579

Soil Types

loam clay

Drainagewell drained

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Growth and flowering are steadiest with 4-6 hours of morning sun and shade through the afternoon, which slows fading of the white petals. Soil should be deep, free-draining loam or clay loam at a pH of 6.5-7.5; standing water in winter kills the root system. Grafted plants are set with the graft union 4-6 inches (10-15 cm) below the soil surface so the tree peony forms its own roots, and suckers arising from the herbaceous rootstock below that point are removed at their origin. Watering deeply every 10-14 days in the first two seasons establishes the root system, after which established shrubs manage on rainfall in most temperate climates. A single application of balanced fertilizer in early spring and a low-nitrogen feed after flowering is sufficient; heavy nitrogen produces soft shoots and increases botrytis. Removing and discarding fallen leaves and blighted buds each autumn reduces the botrytis carryover into spring.

Pruning

P. rockii needs little pruning and resents hard cutting back, since flower buds form on wood made the previous season. Cutting out dead, damaged, and crossing stems at their base in early spring, before growth starts, keeps the framework open. Spent flowers are cut back to the first full leaf, which prevents seed set and keeps the plant putting resources into next year buds. Stems cut into old bare wood below the lowest living bud generally fail to resprout.

Pruning Schedule

Prune: March

early spring