Lemon balm (Melissa officinalis), which grows in U.S. Department of Agriculture plant hardiness zones 3 through 10, is a culinary herb with ornamental value. A close relative of mint (Mentha spp., USDA zones 4 to 9), lemon balm grows 2 to 4 feet tall and spreads 1 to 2 feet.
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Herb and Vegetable Garden
Grow lemon balm in the herb garden for its edible, fragrant leaves which taste like mint with a hint of bright citrus. Harvest the leaves fresh throughout the growing season by picking a few stalks from each plant. Use lemon balm fresh to make tea, add it to light stir fries and vegetable dishes, and use it in drinks, desserts and salads.
Lemon balm attracts bees as it blooms all summer long. Plant it in the herb and vegetable garden, in pots or in the ground, to entice these important pollinators.
You can grow lemon balm as a culinary herb or as an ornamental alone or grouped with other plants in containers. Use standard potting soil and a pot that has drainage holes to keep the roots from getting waterlogged. Use an 8- to 12-inch diameter or larger pot for a single lemon balm plant.
With its spreading growth habit, ability to thrive in part shade and full sun, and delicate flowers in summer, lemon balm works exceptionally well in border areas. Use it to transition from a partly shaded spot to a sunny area in the garden. Grow lemon balm as a tall ground cover in perennial gardens and shrub beds. In USDA zones 9 through 10, lemon balm is an evergreen perennial that will continue growing year-round.
Unlike its close relative mint, lemon balm doesn't spread aggressively and invasively from the roots. Mint will take over a garden when not contained, but lemon balm will spread more slowly.
Sun, Soil and Spacing
Grow lemon balm in full sun -- six plus hours per day -- or part shade -- four to six hours per day. It needs soil that drains well, tolerating sandy soil with poor nutrients. In clay soil, areas with standing water and poorly drained areas, lemon balm struggles to thrive. Plant lemon balm 20 to 24 inches apart.
In part shade, lemon balm retains a deeper, lush green color on the leaves.
Watering and Fertilizing
Water lemon balm slowly until the soil is damp 12 inches deep, then allow the soil to dry out 3 inches deep between watering.
Fertilize in the spring as new shoots start to appear to encourage a strong growing season. Use a general-purpose fertilizer, such as a 10-10-10 product, that supplies balanced nutrients. Sprinkle about 2/3 cup granular fertilizer per 25 foot row of lemon balm, but follow your brand's label directions for specific directions. When applying, leave 3 inches of space between the base of each plant and the fertilizer. Water thoroughly after fertilizing. Repeat the same fertilizer application in the fall after harvesting the leaves.
Trimming and Pruning
If lemon balm bets too big for the space, you can cut it back in the summer. Otherwise, let it grow and fill out through the growing season. To cut back lemon balm, shear all the stalks down to 1 to 2 inches from the top of the soil using a pair of pruning shears. While not an essential step, this keeps lemon balm looking vigorous and fresh, and it keeps it under control.
Once the flower heads start to go to seed through the summer and fall, and the bees have given up trying to get pollen from them, pinch them from the plant at the base. This practice, called deadheading, will keep lemon balm seeds from spreading.
Keep diseases from potentially spreading in the garden by cleaning your pruning shears before and after trimming lemon balm. Dip the blades in a solution of equal parts rubbing alcohol and water, or 1 part bleach to 3 parts water for 5 minutes, then allow to air dry.