Oregano and mint are both members of the Lamiaceae, or mint family, but they spread through the garden in fundamentally different ways. While oregano can spread, it lacks the aggressive, invasive growth habit of true mint species. Mint is notorious for its ability to quickly colonize an area. Understanding the specific botanical mechanisms of each plant clarifies why mint is often contained in pots, while oregano is merely managed.
Understanding Growth Mechanisms
Mint species, such as peppermint and spearmint, owe their reputation for invasiveness to specialized underground stems called rhizomes. These horizontal, modified stems grow beneath the soil surface, sending out new shoots and roots from their nodes. This network of subterranean runners allows mint to rapidly colonize an entire flowerbed, making it difficult to eradicate once established. Even a small piece of a root left behind can quickly sprout into a new plant.
Oregano, by contrast, does not typically produce the deep, fast-spreading rhizomes that characterize mint’s growth. Although some sources describe common oregano (Origanum vulgare) as “rhizomatous,” its underground spread is much less forceful than that of the Mentha genus. The primary difference is the degree of aggression; mint’s runners actively seek out new territory, while oregano tends to expand outward from its central base in a predictable fashion. While oregano will expand, it rarely “wanders” to the extent that mint does.
Oregano’s Clumping and Seeding Habits
Oregano primarily grows as a clumping perennial, gradually increasing the diameter of its central base each season. This expansion occurs through short, near-surface runners, sometimes called stolons, which root where they touch the ground. The common species, Origanum vulgare, is the most vigorous of the culinary oreganos and can quickly form patches up to two feet wide.
The most significant cause of unexpected oregano spread across a garden is self-seeding. If the plant is allowed to flower, it produces thousands of tiny seeds that can be spread by wind, insects, or birds, allowing new plants to pop up far from the original location. This makes the plant seem more invasive than its root structure suggests, as volunteer seedlings often appear in distant garden beds. The aggressiveness of the plant can also vary greatly; varieties like Greek oregano (O. vulgare subsp. hirtum) are often considered less aggressive than the wild-type common oregano.
Practical Containment and Management
Managing oregano involves addressing its propensity to clump and its habit of self-seeding, rather than focusing solely on deep root containment. To prevent new plants from establishing, the most effective technique is regular deadheading, which means removing the flowers before they set seed. Harvesting the stems frequently for culinary use, especially just before the plant begins to bloom, serves the dual purpose of providing fresh herbs and preventing seed production.
For controlling the lateral spread of the central clump, dividing the plant every few years is the best practice. This process involves digging up the mature plant and using a spade to separate the rootball into smaller sections, which rejuvenates the plant and keeps it confined. Planting oregano in a bottomless container sunk into the ground, a technique often used for mint, is an option, but it is not strictly necessary for most varieties. Regular trimming of any wayward stems that attempt to root will also help maintain boundaries.