Peonies are generally not considered invasive plants, though their vigorous growth and remarkable longevity can lead some gardeners to wonder if they are aggressive or difficult to manage.
Understanding Invasive Plants
An invasive plant is a non-native species whose introduction causes, or is likely to cause, economic or environmental harm, or harm to human health. These plants spread aggressively, outcompeting native flora and disrupting ecosystems. They often exhibit rapid growth, high seed production, or extensive root systems, allowing them to dominate new environments.
It is important to distinguish invasive plants from aggressive or vigorous growers within a cultivated garden. Aggressive plants might spread rapidly or outcompete others in certain situations but do not cause ecological harm beyond the garden. Invasive species, however, pose a significant threat to biodiversity by displacing native species and altering habitats.
Peony Growth Habits
Peonies are long-lived perennials that form a clump, gradually expanding from their central crown and root system. They remain in the same location for decades without needing division.
Two main types exist: herbaceous and tree peonies. Herbaceous peonies die back each fall, with new shoots emerging from underground tubers in spring. Their substantial root systems do not produce runners or self-seeded offspring that readily escape cultivation. Tree peonies are woody shrubs that retain their stems year-round, maintaining a contained, shrub-like form.
A mature peony clump can become large, reaching 3 to 4 feet tall and wide for herbaceous varieties, and up to 7 feet tall and 5 feet wide for tree peonies. However, their spread is localized. They do not outcompete other plants beyond their immediate vicinity in a managed garden, nor do they produce seeds that colonize wildlands. Their growth is predictable and contained.
Managing Peony Growth
Managing peony growth involves routine care and occasional intervention for plant health or propagation. Proper spacing at planting is important, as peonies grow to a significant size; planting them 3 to 4 feet apart ensures adequate air circulation and prevents overcrowding. Their substantial root systems can extend up to 3 feet across, so ample space allows for healthy development.
For established herbaceous peonies, division can manage size or create new plants, though it is not required for their health. This process involves digging up the plant in the fall, dividing the root clump into sections with several “eyes” (buds) and a healthy root system, then replanting. Tree peonies, with their woody stems, are best left undisturbed and do not require division.