Lemon balm (Melissa officinalis) is a fragrant perennial herb prized for its gentle lemon scent and historical use in culinary and medicinal applications. This member of the mint family (Lamiaceae) is a popular addition to many home gardens, often used in teas and salads. Successfully growing this herb alongside others requires careful planning, as its vigorous nature can quickly overpower less aggressive neighbors.
Lemon Balm’s Aggressive Growth Habits
Lemon balm’s difficulty as a garden companion stems primarily from its dual methods of rapid reproduction. Like many plants in the mint family, it spreads aggressively through self-seeding and underground runners, or rhizomes. The plant can reach a height of two to three feet in a single season, forming dense, mounding clumps.
The primary concern is the prolific self-seeding, which allows the herb to colonize new areas quickly once its flowers mature. These seeds germinate readily, creating a dense monoculture that prevents sunlight and air from reaching other plants. While it also uses rhizomes, which are underground stems, the sheer volume of volunteer seedlings is often the most significant threat to a mixed garden bed. This aggressive growth establishes a heavy demand for resources, quickly depleting the surrounding soil of water and available nutrients like nitrogen.
Specific Plants That Suffer From Competition
Many herbs and garden vegetables cannot compete with the growth rate and resource demands of lemon balm. Delicate herbs, especially those with slower growth cycles, are susceptible to being overwhelmed. Plants like basil and thyme are easily shaded out by the tall, bushy growth of lemon balm, restricting the necessary sunlight they need to thrive. This physical competition often leads to stunted growth and reduced yields.
Incompatibility also arises from mismatched environmental needs, particularly concerning soil moisture. Herbs native to arid or Mediterranean climates, such as lavender, rosemary, and sage, prefer lean, well-drained soil that dries out between waterings. Lemon balm, by contrast, requires consistently moist conditions and rich soil to maintain its lush foliage. Planting these together creates a situation where the drought-tolerant plants risk root rot from the excess water, or the lemon balm becomes stressed if the soil is kept too dry.
Even other members of the mint family, such as mint and oregano, should not be planted directly next to lemon balm. Although they share the vigorous spreading habit, they will compete fiercely for the same limited space and nutrients. This competition often results in both plants performing poorly. Furthermore, the close proximity of herbs with strong volatile oil profiles can lead to an undesirable alteration in the flavor of the harvested leaves.
Strategies for Containment and Separation
The most effective method for preventing lemon balm from overtaking a garden is to control its spread before it becomes established. Planting the herb in a container is widely recommended, as the physical barrier prevents the horizontal spread of rhizomes. For planting in a garden bed, sinking a large, bottomless pot into the soil acts as a subterranean root barrier that restricts the herb’s territory. Pots should be at least 25 to 30 centimeters in diameter and depth to accommodate the plant’s robust root system.
Controlling the prolific self-seeding tendency requires aggressive pruning and deadheading. Gardeners should trim off the flower heads as soon as they appear, and certainly before they have a chance to set seed. Regular harvesting and cutting the plant back several times a season prevents seed formation and encourages a fresh flush of flavorful leaves. Applying a thick layer of organic mulch around the base of the plant can also help suppress the germination of any seeds that fall to the soil surface.