Types of peonies: herbaceous, tree, intersectional

I've grown peonies in my zone 7a Long Island garden for over 15 years. The first peony I planted was a pale pink herbaceous type bought at a big-box store with no cultivar name on the label. It bloomed the following May in large double flowers that nodded to the ground in the first rain and has.

I've grown peonies in my zone 7a Long Island garden for over 15 years. The first peony I planted was a pale pink herbaceous type bought at a big-box store with no cultivar name on the label. It bloomed the following May in large double flowers that nodded to the ground in the first rain and has since grown into a substantial clump that blooms reliably every spring.

The three main peony types — herbaceous, tree, and intersectional — differ in cold hardiness, when they bloom, what happens to their stems in fall, and critically in how deep to plant them. The planting depth rules are different for each type, and confusing them is the most common cause of failure.

Herbaceous peonies (Paeonia lactiflora and hybrids)

Herbaceous peonies die completely to the ground each fall and regrow from fleshy storage roots each spring. They are the most widely available peony type and the most cold-hardy.

Per Penn State Extension, herbaceous peonies are reliably hardy in USDA zones 3–8. They require a cold dormancy period of approximately 300–500 hours below 40°F, which limits their performance in zone 9 and warmer.

Planting depth: Per Penn State Extension, the most critical rule in herbaceous peony culture is planting depth. Eyes (red growth buds on the crown) must be no more than 1–2 inches below the soil surface in zones 4–7. Eyes planted deeper than 2 inches may produce vigorous foliage but will not bloom. This is the most common reason peonies fail to bloom.

Flower forms in herbaceous peonies:

Per Missouri Botanical Garden, double-flowered types are the most popular but tend to flop in rain due to the weight of the flower head. Single and Japanese forms have better stem strength and are more accessible to pollinators.

Bloom season: In zone 6–7, herbaceous peonies bloom May–June. By choosing early-, mid-, and late-season cultivars, the bloom window can be extended over 4–6 weeks.

Tree peonies (Paeonia suffruticosa and related species)

Tree peonies are woody shrubs that retain their stems year-round, reaching 3–6 feet tall at maturity. They bloom 2–4 weeks before herbaceous peonies in the same zone and produce flowers 6–12 inches across — larger than any other peony type.

Per NC State Extension, tree peonies are hardy in zones 4–9 but need protection from desiccating winter wind in zones 4–5.

Planting depth: Per Missouri Botanical Garden, tree peonies are grafted plants. The graft union must be buried 4–6 inches deep to encourage the ornamental top to develop its own roots and reduce dependence on the rootstock. This is the opposite of herbaceous peony planting depth.

I don't grow tree peonies at my Long Island garden — I don't have a location that offers both wind protection and full sun with adequate space for a 5-foot shrub. The information here comes from Extension publications.

Selected tree peony cultivars:

Per Penn State Extension, tree peonies grow slowly — 2–3 inches per year initially. Do not cut them back in fall; they retain their woody structure through winter.

Intersectional (Itoh) peonies (Paeonia × itoh)

Intersectional peonies, also called Itoh peonies, are hybrids between herbaceous and tree peonies, first developed by Japanese breeder Toichi Itoh in the 1940s. Per Clemson HGIC, they combine the cold hardiness of herbaceous types (zones 3–8) with the flower color range and disease resistance of tree peonies.

Planting depth: Follow the herbaceous rule — eyes 1–2 inches below soil surface.

Key characteristics:

• Stems die back partially or fully in fall (unlike tree peonies which retain stems)
• Flower multiple times per stem in a season (unlike herbaceous types)
• Excellent resistance to botrytis blight
• Colors include yellow, orange, and bicolors unavailable in herbaceous types
• Expensive ($30–80 per bare-root plant)

Selected Itoh cultivars:

Side-by-side comparison

Frequently asked questions

Do peonies need ants to bloom? No. Per Cornell Cooperative Extension, this is a persistent myth. Ants are attracted to the sugary exudate on peony buds but play no role in flower opening. Peony buds open normally without ant activity, and ants do not damage the flowers.

How long do peonies live? Herbaceous and intersectional peonies can live for 100 years or more if properly sited. Per Missouri Botanical Garden, herbaceous peonies from the 19th century are still found in abandoned garden sites. Tree peonies similarly live for decades to over a century. Do not divide peonies unless they are overcrowded (typically after 20+ years) — division reduces vigor and delays bloom.

Can I grow peonies in zone 9? Per Cornell Cooperative Extension, herbaceous peonies require 300–500 hours below 40°F for adequate dormancy. Most of zone 9 does not reliably provide this. Gardeners in zone 9 should choose early-blooming cultivars and expect reduced performance. Tree peonies perform better in zone 9 than herbaceous types.

What is the best white herbaceous peony? Per Penn State Extension, 'Festiva Maxima' (double white with crimson flecks; 1851; zones 3–8) and 'Duchesse de Nemours' (double white; fragrant; 1856) are the most reliable white herbaceous peonies. 'Bowl of Cream' (double white Itoh) is the most-awarded white intersectional.

Sources

1. Penn State Extension — Peonies
2. Missouri Botanical Garden — Paeonia lactiflora
3. NC State Extension — Peonies
4. Clemson HGIC — Growing Peonies
5. Cornell Cooperative Extension — Peonies