The seeds need temperatures of around 20?C (68?F) to germinate. They require consistently moist soil; do not let them dry out in between watering. Transplant when they have their first set of true leaves and are still small Lemon balm plants should be spaced 30 to 38cm (12 to 15 in) apart. Keep the soil moist, but well drained. The seeds do require light to germinate. Harvest leaves from your lemon balm plant at any time.