Bee balm (Monarda species) is a popular garden perennial known for its bright, whorled flowers that attract hummingbirds, bees, and butterflies. A member of the mint family, this North American native is highly valued for supporting local pollinator populations. However, its vigorous growth habit often leads gardeners to question if its aggressive spreading tendency makes it a true ecological threat.
Aggressive Spreader vs. True Invasive Species
The term “invasive” is often used to describe any plant that spreads rapidly in a garden setting, but its ecological definition is far more specific. A true invasive species is a non-native organism that causes economic or environmental harm by out-competing native plants. Bee balm, including species like Monarda didyma and Monarda fistulosa, is native to North America. Due to its native status, it cannot be classified as an invasive species in the United States, even if it spreads vigorously in a cultivated garden bed. Bee balm is instead described as an “aggressive spreader” or “horticulturally aggressive” plant. This distinction acknowledges its potential to become a nuisance without labeling it as an ecological threat.
Mechanisms of Spread
Bee balm’s spreading reputation stems from its subterranean growth habit, characteristic of the mint family. The plant rapidly produces horizontal underground stems, known as rhizomes or runners, which extend outward from the original clump. These rhizomes send up new shoots, quickly establishing new plants around the perimeter. This continuous outward growth allows a single plant to form a dense patch that expands significantly each season.
In ideal conditions—rich, moist soil and full sun to partial shade—this rhizomatous growth is particularly pronounced. Over several years, this pattern can cause the center of the original clump to die out, leaving a ring of newer, vigorous plants. While rhizomes are the primary method of spread, bee balm also reproduces via seed. If spent flowers are not removed, the plant will readily self-seed, allowing new plants to appear in distant parts of the garden.
Containment and Control Methods
Managing bee balm’s aggressive spreading requires proactive intervention, focusing on controlling both rhizomes and seed production. The most effective cultural control method is routine division, performed every two to three years to maintain plant vigor and limit spread. In early spring, as new shoots emerge, the entire clump should be dug up. The outer, most vigorous sections should be separated and replanted, and the older, woody center discarded.
To prevent rhizomes from invading adjacent garden space, physical barriers can be installed. A metal or plastic root barrier placed vertically into the soil, extending at least 12 to 18 inches deep, effectively blocks the horizontal spread of the runners. Another method is to plant bee balm directly into a large container, such as a five- to ten-gallon pot, and then sink the pot into the ground. This “pot-in-the-ground” technique completely contains the rhizomes, limiting the plant’s spread.
Controlling spread by seed is achieved through deadheading, which involves removing spent flower heads before they mature and drop seeds. Removing faded flowers encourages a longer bloom period and prevents the plant from reproducing. By combining regular division with physical containment and deadheading, gardeners can enjoy bee balm’s vibrant flowers and pollinator appeal without allowing it to overwhelm the landscape.