Bee balm (Monarda) is a popular garden perennial known for its colorful, shaggy flowers that attract hummingbirds and other pollinators. As a member of the mint family (Lamiaceae), this plant has a vigorous growth habit that quickly expands beyond its initial planting location. Understanding the dual mechanisms by which bee balm spreads—through underground runners and by seed—is necessary for managing its presence in a cultivated setting.
Spreading via Underground Runners
The primary way bee balm expands its territory is through the aggressive growth of underground stems called rhizomes. These specialized stems grow horizontally beneath the soil surface, acting as cloning mechanisms for the parent plant. Rhizomes are distinct from roots; they contain nodes from which new roots and vertical shoots (ramets) emerge.
As rhizomes push outward, new shoots continually sprout up, forming an ever-widening, dense clump of genetically identical plants. This horizontal expansion is often rapid, creating a thick mat of shallow roots and runners just beneath the topsoil. The center of the initial clump may eventually become woody and die out, forcing the plant’s active growth to the edges as it seeks new soil.
The speed and intensity of this rhizomatous spread depend significantly on the growing conditions, with moist, rich soil encouraging the most vigorous expansion. Some species, like Monarda didyma (Scarlet Bee Balm), are known for particularly aggressive rhizomes. While this mechanism ensures the plant’s survival and creates a robust stand, it is the main challenge for gardeners trying to keep the perennial contained within a border.
Spreading via Seed Dispersal
The secondary method of bee balm propagation is through self-seeding, which introduces new, genetically unique plants to the garden. After the tubular flowers fade, they produce clusters of tiny, nutlet-like seeds within the dried flower heads in mid-to-late summer. When the mature seed heads dry and shatter, wind and weather disperse the small seeds a short distance from the parent plant. Successful germination is most likely in areas with bare soil, as mulch significantly reduces the success rate by preventing seeds from reaching the ground.
If the seeds are left on the plant over winter, they can serve as a food source for seed-eating birds, which may deposit them elsewhere in the landscape. Unlike rhizome spread, which creates clones that expand the original mass, seed dispersal results in offspring that pop up in entirely new, often unexpected locations.
Controlling and Directing Growth
Managing the robust growth of bee balm requires targeted intervention against both the rhizomes and the seeds. To control the aggressive underground spread, gardeners should plan to dig up and divide the clumps every two to three years, ideally in the early spring as new growth begins. This process involves removing the woody, unproductive center and replanting only the vigorous outer sections.
Physical barriers can also be installed to restrict rhizomes, such as burying a plastic or metal root barrier 12 to 18 inches deep around the planting area. Container planting is another simple method that completely restricts rhizome growth, allowing the plant to be enjoyed without overwhelming neighboring plants.
To limit the spread of new plants from seed, a practice called deadheading is highly effective. Deadheading involves promptly removing the spent flower heads before the seeds ripen and drop, which prevents the majority of self-sowing. If a gardener wishes to encourage growth, they can intentionally leave a few spent flower heads to drop seed or use the divisions created during spring maintenance.