Lemon balm ( _Melissa officinalis_ ) is a popular herb known for its refreshing lemon scent and diverse culinary and medicinal applications. Successful cultivation relies on appropriate temperature conditions. Understanding temperature’s influence on its growth and health is key to a thriving plant.
Ideal Growing Temperatures
Lemon balm thrives in a temperate climate, preferring a range between 68°F and 77°F (20°C to 25°C). While it can tolerate temperatures up to 95°F (35°C), this narrower range promotes vigorous leaf production and enhances essential oil development. During cooler seasons, maintaining temperatures above 32°F (0°C) is sufficient for overwintering.
For germination, lemon balm seeds germinate best when soil temperatures are between 65°F and 75°F (18°C and 24°C). This warmth encourages quick sprouting. Once established, the plant benefits from a slight temperature drop at night, which mimics its natural Mediterranean habitat and supports vigor.
How Temperature Affects Growth
Temperatures outside the ideal range can impact lemon balm’s health and productivity. When temperatures drop below 15°F (-10°C), leaves brown and wilt from cold stress. Although lemon balm is cold-hardy, prolonged exposure to freezing conditions can cause significant damage or kill it. In extremely cold winters, the plant may die back to the ground, re-sprouting in spring as temperatures rise.
Conversely, excessive heat harms the plant. When temperatures exceed 95°F (35°C), leaves may lighten in color, curl, or become susceptible to sunburn. High heat can also lead to bolting, where the plant prematurely flowers and seeds, reducing flavor and toughening leaf texture. Prolonged exposure to intense heat can cause wilting, drooping, and a decrease in aromatic qualities due to essential oil degradation.
Protecting Lemon Balm from Temperature Extremes
To protect lemon balm from cold temperatures, several strategies help. Mulching around the plant in the fall helps insulate the soil and roots, preventing deep freezes. For potted lemon balm, bringing plants indoors to a bright, cool location (around 40-50°F or 5-10°C) during winter provides a resting phase. If temperatures are expected to drop significantly below freezing, covering outdoor plants with horticultural fabric or a thick layer of leaves offers additional protection.
During hot periods, providing afternoon shade is important. Planting lemon balm in a location that receives morning sun but is shaded during the day’s hottest parts helps prevent leaf scorch and bolting. Adequate watering is important to keep soil moist, not waterlogged. Container plants may need frequent watering as pots dry out quickly. Proper spacing allows for good air circulation, mitigating heat stress.