Lemon balm (Melissa officinalis) is a perennial herb belonging to the mint family, cherished for its light, lemony fragrance and flavor. It is popular in culinary applications, such as teas and flavorings. Starting lemon balm from its tiny seeds can sometimes prove challenging for new growers. Understanding the specific requirements for successful seed germination is the first step toward cultivating this herb.
Essential Conditions for Success
Lemon balm seeds exhibit photoblastism, meaning they require exposure to light to break dormancy and begin germination. This is a crucial distinction from many other seeds that need to be buried deeply. The seeds must be surface-sown, or at most, pressed gently into the growing medium, to ensure they receive the necessary light signal.
Maintaining the correct temperature is equally important for prompt sprouting. The ideal soil temperature range for germination is relatively warm, between 65 and 75°F (18–24°C). Within this temperature window, seedlings should emerge within 7 to 14 days, though germination can take up to 21 days in cooler conditions.
The growing environment demands a sterile, finely textured seed-starting mix to prevent fungal diseases like “damping off.” This medium must retain consistent moisture without becoming waterlogged, as the seed embryo can easily die if the soil dries out. A good seed mix will be loose and well-draining, providing the perfect balance of hydration and aeration for the emerging roots.
Step-by-Step Sowing Instructions
Begin by selecting a clean seed tray or small containers that have drainage holes. Fill the containers with the sterile, fine-textured seed-starting mix, ensuring the surface is level and gently firmed down. Water the medium thoroughly from the bottom or mist the surface until it is uniformly damp before sowing.
Scatter the lemon balm seeds thinly across the prepared surface of the moist soil. Since they are light-dependent, do not cover the seeds with soil. Instead, lightly tamp them down with a flat object or your finger to ensure good contact with the medium while keeping them exposed to light.
To maintain consistent high humidity and moisture, cover the container with a clear plastic dome or plastic wrap. Place the covered tray in a location that provides bright light, such as under grow lights set for 12–16 hours daily, or on a sunny windowsill. Ensure the ambient temperature remains within the optimal 65–75°F range, perhaps using a seedling heat mat to regulate the soil temperature.
Caring for Seedlings Until Transplant
Once the tiny seedlings emerge, manage the humidity to prevent disease. While the cover is necessary for germination, it must be removed or vented soon after sprouting to introduce air circulation and prevent damping off. Gradually lift the humidity dome once a day, increasing the time until the cover is removed entirely when the seedlings develop their first set of true leaves.
Keep the soil consistently moist but never soggy; bottom watering is a good technique, allowing the medium to wick up moisture from a shallow tray. When the seedlings have developed two sets of true leaves, thin them out to provide adequate space and resources. Gently snip the weakest seedlings at the soil line with small scissors, leaving the remaining plants spaced well apart.
Six to eight weeks after sowing, and once all danger of frost has passed, the young plants will be ready to move outdoors. Before the final transplant, the seedlings must undergo “hardening off.” This gradual process involves exposing them to outdoor conditions—sun, wind, and temperature fluctuations—for increasingly longer periods over one to two weeks to reduce transplant shock.