Paeonia lactiflora (herbaceous peony) and tree peonies (Paeonia suffruticosa) differ significantly in their growth habits. Herbaceous peonies are perennial plants that die back to the ground each winter and regrow from their roots in spring. They typically reach heights of 2–3 feet (60–90 cm) and have soft, green stems. In contrast, tree peonies are woody shrubs that retain their structure year-round, with stems that become woody and can grow up to 4–7 feet (1.2–2.1 meters) tall. Their woody framework allows them to support larger, more robust blooms.
The root systems of these two peony types also vary. Paeonia lactiflora develops thick, fleshy storage roots that store nutrients for winter dormancy and spring regrowth. These roots should be planted shallowly, with the "eyes" (buds) no more than 2 inches (5 cm) below the soil surface. Tree peonies, however, are often grafted onto herbaceous peony rootstock and require deeper planting. The graft union should be buried 4–6 inches (10–15 cm) below the soil to encourage the tree peony to develop its own roots.
Both types thrive in well-draining, fertile soil, but their sunlight needs differ slightly. Herbaceous peonies prefer full sun (6+ hours daily) for optimal blooming, though they can tolerate light shade in hotter climates. Tree peonies, while also sun-loving, benefit from partial shade in regions with intense afternoon sun to protect their delicate petals from scorching. Both dislike waterlogged soil, but tree peonies are slightly more drought-tolerant once established due to their woody structure.
Paeonia lactiflora requires consistent moisture during its growing season but should not be overwatered, as soggy soil can lead to root rot. A balanced fertilizer applied in early spring supports growth. Tree peonies, with their deeper root systems, need less frequent watering but benefit from a slow-release fertilizer high in phosphorus to promote blooming. Over-fertilizing tree peonies, especially with nitrogen, can lead to excessive foliage at the expense of flowers.
Herbaceous peonies require minimal pruning; simply cut back dead stems to the ground in late autumn to prevent disease. Tree peonies, however, need careful pruning to maintain shape and encourage airflow. Remove dead or weak wood in late winter or early spring, but avoid heavy pruning, as they bloom on old wood. Unlike herbaceous peonies, tree peonies should never be cut to the ground.
Paeonia lactiflora is highly cold-hardy (USDA zones 3–8) and relies on winter dormancy to trigger spring growth. Tree peonies are slightly less cold-tolerant (zones 4–9) and may need winter protection in harsh climates. Their woody stems can suffer frost damage, so mulching the base is recommended in colder regions. Both types require a period of chilling to bloom well.
Herbaceous peonies bloom in late spring to early summer, with flowers lasting about 7–10 days. Their stems are often not strong enough to support the heavy blooms, requiring staking. Tree peonies bloom earlier in spring, with larger, longer-lasting flowers (up to 2 weeks) and sturdier stems that rarely need support. Their blooms come in a wider range of colors and forms, including single, double, and semi-double varieties.
Both are susceptible to botrytis (gray mold) and fungal diseases, but herbaceous peonies are more prone to stem wilt due to their soft growth. Tree peonies may face issues with scale insects or borers attacking their woody stems. Good air circulation, proper spacing, and avoiding overhead watering help prevent problems for both types.
