Mountain Mint: A Pollinator Powerhouse

Mountain mints are plants in the genus Pycnanthemum, whose name comes from the Greek words pyknos, meaning dense, and anthos, meaning flower, referring to their densely packed flowers. While they are in the mint family (Lamiaceae), they are more closely related to wild bergamot or bee balm (Monarda spp.) than true mints (Mentha spp.).  Like other members of the mint family, they have square stems and their foliage has a strong fragrance, and deer, rabbits, groundhogs, or voles rarely browse them.

Spreading by shallow rhizomes, mountain mints grow vigorously but are not as invasive as other "mints." To keep plants in check and prevent them from spreading into unwanted areas, prune the roots in the spring with a shovel or spade. Hardy in USDA Hardiness Zones 3 through 8, they will grow in full sun to part shade but will have the best flowering in full sun. They prefer medium to high moisture and fertile, well-draining soils but will tolerate clay soils, and once they become established, they will be drought tolerant.

Densely packed clusters of small flowers bloom at the terminal ends of the upper stems from July through September. Their flowers are two-lipped, tubular in shape, and are white to lavender, often with small purple spots. Despite not having large or showy blooms, these long bloomers are pollinator magnets. The Penn State Southeast Agricultural Research and Extension Center conducted a study from 2012 through 2015, comparing 86 species and cultivars of native plants known for their attractiveness to pollinators. Clustered mountain mint (Pycnanthemum muticum) was determined to have the most pollinator visits and attracted the most diverse group of pollinators, including bees, butterflies, wasps, syrphid, and tachinid flies.

Mountain mints generally form erect, bushy clumps or tall, spreading ground covers. Considered weedy by some, plant them in an area where they can naturalize and create a large mass or drift. They can be a perfect choice for a cottage garden, sensory garden, or pollinator garden. They can be a great addition to fresh or dried flower arrangements. Once they have stopped flowering, allow their seed heads to remain for winter interest and as a food source for birds.

There are an estimated twenty species of mountain mint, with eight species native to Pennsylvania. The five listed below are commonly found in nurseries.

Virginia mountain mint, American mountain mint, or common mountain mint (P. virginianum) grows up to 3 feet in height with green or red stems. Its narrow, green, lance-shaped leaves are 1 to 3 inches long and ¼  to ½ inches wide. Small, white flowers form numerous ¾-inch flat clusters that may contain up to 50 flowers. These bloom a few at a time, beginning with the outer flowers and moving to the center over the course of a season.

Hoary mountain mint (P. incanum) has an erect, many-branched habit and typically grows to a height of 2 to 4 feet but may grow up to 6 feet. Hoary, meaning grayish white, aptly describes the whitish appearance of the upper leaves and bracts of this species of mountain mint. Its 1.5 to 4-inch leaves are oval with toothed margins and have white, downy undersides. When grown in full sun, after blooming, its foliage may develop a reddish color. The silvery foliage pairs well with plants with darker foliage.

Narrow-leafed mountain mint or slender mountain mint (P. tenuifolium) grows 2 to 3 feet in an upright clump. The Latin tenuifolium means slender-leaved and refers to its 1 to 2-inch green, needle-like leaves that create finely textured foliage. Its flower clusters are slightly rounded and composed of numerous, small, two-lipped flowers varying from whitish to lavender, with purple spots.

Broad-leaved mountain mint or clustered mountain mint (P. muticum) will grow to a height of 2 to 3 feet. Its green leaves are 1–3 inches long and wide and ovate with broad-toothed margins.  Clusters of tiny, two-lipped, white to light pink blooms rise just above a pair of silvery bracts that give the plants a frosted, snowy appearance. Its rhizomes tend to spread more than other species, sometimes over 4 feet, so it is good to pair them with other assertive species such as wild bergamot (Monarda fistulosa), black-eyed Susans (Rudbeckia spp.), and garden phlox (Phlox paniculata).

Appalachian mountain mint (P. flexuosum) grows to a height of 2 to 3 feet with foliage smaller than broadleaf mountain mint but not as thin as the Virginia or narrow-leaved species. Green, oval to lance-shaped, toothed leaves will develop a red coloration in the fall. These plants boast flower clusters that are somewhat larger and showier than other species. Their tiny tubular flowers form dense, 1½-inch, globe-shaped clusters. Each flower has five off-white sepals that protect the flower bud and then support the flower when open. Once the flowers fade, the sepals remain, giving the globular head a prickly appearance.