Among the more forgiving plants in the perennial world, lemon balm (Melissa officinalis), which grows in U.S. Department of Agriculture plant hardiness zones 3 through 7, tolerates a broad range of climates and soils. This citrus-scented herb, which also adds zest to drinks and foods, has ornamental value and practical uses in the garden. This makes it a much-valued and versatile companion plant.
To Cover Shrub Bases
Lemon balm, which is shrubby and grows at least 2 feet tall, acts as a ground cover under plants that are notoriously "leggy" at their bases. Plant lemon balm at the base of such shrubs as beautyberry (Callicarpa spp., USDA zones 5 through 10) and roses (Rosa spp., USDA zones 3 through 11) or any shrubs that have become bare at the bottom. Because lemon balm takes some shade, it will tolerate overhanging branches that block sun.
In the Vegetable Patch
Whether it be its role as a pollinating plant, its strong, insect-inhibiting fragrance, or its ability to control weeds, lemon balm has a reputation for enhancing the growth of other edibles. Grow it near cabbages (Brassica oleracea var. capitata) or squash plants (Cucurbita spp.) to ward off pests. While some of the lore about lemon balm as an ally to vegetables remains anecdotal, it's certainly a striking ornamental perennial to grow among annual vegetables.
When you have room for lemon balm to spread out, grow it among plants that like the same conditions it does. This approach gives you a range to choose from, given that lemon balm likes sun or light shade, lightly moist soil and also tolerates both cold and warm weather. Use its sprawling foliage as a contrast to more upright plants, such as chives (Allium schoenoprasum, USDA zones 3 through 10) or lovage (Levisticum officinale, USDA zones 4 through 8).
Lemon balm is known as an beekeeper's friend and an orchard herb because its flowers attract honeybees, which pollinated fruit trees. Even if you don't have an orchard, encircling fruit trees with lemon balm will do double-duty as weed-suppressing ground covers and as bee-lures to increase fruit production.