Lemon balm can be on indoor herb, or an outdoor perennial.  If planted outdoors, it likes part sun with a little shade.  If planted indoors, place in a sunny spot.  If allowed to bloom the leaves will become bitter.  Pinch off blooms as soon as they come if going to harvest leaves.  Start harvesting as soon as plant is established.  Don't harvest more than 25 percent of plant at one time, it will damage the plant.  Water when plant is dry, or starting to wilt.  Hardiness zone: 4-9