Lemon balm (Melissa officinalis) and mint (Mentha species) are aromatic herbs highly favored for their fragrant leaves and culinary uses. Both belong to the Lamiaceae family, commonly known as the mint family. Due to their similar appearance and shared preference for growing conditions, many gardeners wish to cultivate these popular herbs side-by-side.
The Direct Answer: Co-planting Feasibility
It is technically possible to plant lemon balm and mint in the same area, but this requires significant preventative measures. The primary challenge is their aggressive growth habit, shared as members of the mint family. Both plants naturally seek to dominate their environment and will compete fiercely for resources if left unchecked. This competition can quickly lead to one or both plants becoming stunted.
Mint species spread rapidly through extensive underground runners known as rhizomes, creating a dense, invasive root network. Lemon balm shares this root-spreading tendency, though often less aggressively than true mint, and also spreads prolifically by self-seeding. If planted directly into the ground without intervention, the two will eventually engage in a battle for soil territory. Successful co-planting depends entirely on physical separation to manage their territorial root systems.
Managing Aggressive Growth
To effectively co-plant these herbs, physical barriers must be installed to prevent their roots from mingling. The most reliable method involves planting each herb into a separate container before sinking the containers into the soil. These pots should be large (10 to 12 inches in diameter) and made of plastic or terracotta with their bottoms completely removed. This creates a deep wall that contains the horizontal spread of the rhizomes while allowing for drainage and root depth.
When using this sunk-pot method, the rim of the barrier should sit one to two inches above the soil line to prevent runners from escaping over the top. For wide garden beds or raised structures, a permanent root barrier made of thick plastic or metal sheeting can be installed vertically into the soil. This barrier needs to be buried at least 18 inches deep to block the rhizomes, which typically spread in the top layer of soil.
Managing lemon balm’s prolific self-seeding is necessary for long-term control, even with root containment. Regular pruning of the stems before the flowers set seed will prevent new plants from germinating nearby. This practice, known as deadheading, should be combined with regular harvesting to keep both plants bushy and encourage fresh growth throughout the season.
Shared Environmental Needs
Once their aggressive growth is contained, lemon balm and mint share similar requirements that allow them to thrive in the same location. Both herbs are adaptable regarding sunlight, performing best in a range from full sun to partial shade. In regions with intense summer heat, afternoon shade is beneficial to prevent foliage scorching and maintain the potency of aromatic oils.
Both Melissa officinalis and Mentha species prefer rich, well-draining soil that retains consistent moisture. Their vigorous growth demands a steady supply of water, making consistent deep watering important, especially during drought. Over-watering should be avoided to prevent fungal issues such as root rot, but the soil should never be allowed to completely dry out.
The herbs are not demanding in terms of soil fertility and generally do not require heavy feeding. Incorporating organic matter, such as compost, into the soil at the start of the growing season typically provides sufficient nutrients. This simple feeding regime supports lush foliage growth without encouraging excessive, weak stem development.