Mountain Mints - Pycnanthemum species
NABA member Mary Anne Borge shares the following report about mountain mints located in southern New Jersey:
Mountain mints are in bloom right now , and they are covered with a spectacular variety of butterflies, bees, wasps, and moths! These beneficial pollinators all graze for nectar 
contentedly, since these plants provide enough food for everyone simultaneously, and over a long period of time. From morning until evening these plants are alive with the dance of the pollinators.
The bloom period begins in July, and extends at least through August. Like other members of the mint family, these species have clusters of flowers that bloom progressively over a long period of time.
There are several species of mountain mint, but my favorites are short-toothed mountain mint (Pycnanthemum muticum) and hoary mountain mint (Pycnanthemum incanum). The genus name, Pycnanthemum, means densely flowered, hinting at the reason that these plants can accommodate so many hungry visitors simultaneously. The foliage of these two species is as showy as the flowers, extending the period of visual appeal.
Short-toothed mountain mint grows to a height of about 2-3 feet, topped with round heads of tiny white flowers smudged with bright magenta. The plants are truly ‘densely flowered’. The flowers are set off by the leaves that frame them, which a powdery pale blue-green with a velvety looking texture. Rub or crush the leaves and you’ll be rewarded with a sent that confirms that this is a mint family member. After the long bloom period, the flower heads dry to an eye-catching dark gray, making it an attractive plant throughout the winter. 
Short-toothed mountain mint can tolerate part shade to full sun, and likes moist but well-drained, average soil. In this photo, an Eastern-Tailed Blue is stopping for a long drink.
Hoary mountain mint, as the name implies, has foliage very similar to short-toothed mountain mint, with the leaves just below the flower heads looking as if they had been lightly but evenly dusted with powdered sugar. 
The flowers grow in rounded heads much like Short-toothed mountain mint, but the flowers are somewhat larger. Each delicate flower is white with a sprinkling of tiny purple spots. The flowers generally grow in multiple tiers on each stem, with a branching habit that is open and graceful, showing off the additional layers of flowers. An Olive Hairstreak is enjoying this lovely plant’s offerings.
This species also grows to a height of 2-3 feet, prefers sun, and average to dry soil.
The mountain mints may be a gardeners’ dream come true – attractive, easy to grow, and they are deer resistant! [End of Mary Anne's text]
While the different species of mountain mint can be difficult to tell apart, they are all good garden plants and are worth seeking out. Mountain mints are suggested as an alternative garden plant to the (non-native) invasive oxeye daisy (Leucanthemum vulgare) which is an aggressively spreading plant that decreases native plant diversity where it takes hold.
There are over 20 native species of mountain mint in the United States. The following commonly are used in butterfly gardens and are often found for sale in native plant nurseries:
- Hoary Mountain Mint (Pycnanthemum incanum) has a native range as far north as Ontario, south to Florida, with a western range into Illinois. While often found for sale at native plant nurseries, this species is listed as endangered in New Hampshire, Canada, and Vermont.
- Short-toothed Mountain Mint (Pycnanthemum muticum) has a native ranges as far north as Maine, south to Georgia, with a western range into eastern Texas. Also called blunt mountain mint, this species is listed as threatened in Kentucky, Michigan, and New York.
- Narrow-leaf Mountain Mint (Pycnanthemum tenuifolium) has a large native range stretching into Ontario in the north, appearing in northern Florida in it's southern range, and reaching the eastern parts of Kansas and Texas in it's most western locations.
- Virginia Mountain Mint (Pycnanthemum virginianum) covers much of the same range as other mountain mints but also includes upper midwestern states such as South Dakota, North Dakota and Minnesota. Virginia mountain mint is listed as endangered in New Hampshire.