Pycnanthemum tenuifolium is a member of the mint family. Since mints are extremely invasive and difficult to remove from the garden you might be thinking, I’ll pass on this one. But that would be a mistake. This mint is very well behaved and is an insect/butterfly magnet. It is native to the north-east part of North America, including Ontario.
P. tenuifolium is also known as slender mountain mint, narrow leaf mountain mint, Virginia thyme and common horsemint. It is easy to grow in sun or shade, wet or dry. It prefers a spot that is sunny with some moisture, but it is very adaptable. Although some references claim that the plant spreads, the author’s plant has been in the same spot for about 5 years and it has not spread or made any seedlings (ground is mulched with wood chips). It looks good all season, making a nice, light green, lacy bush in spring, and flowering for several weeks in late summer.
The extremely thin leaves are almost needle-like and have a mint-like aroma when crushed. It is distinguished from Pycnanthemum virginianum (common mountain mint), by its hairless stem and the fact that its leaves are less than 6 mm (¼ inch) across. The narrow leaves also distinguish it from the other 20 species of mountain mints.
Life Cycle: perennial
Height: 50cm (2.5 ft)
Bloom Time: mid to late summer
Natural Range: north-east part of North America
Habitat: dry, open, rocky woods, dry prairies, road sides and along streams
Cultivation of Pycnanthemum tenuifolium:
Light: full sun to part shade
Water: dry to wet
USDA Hardiness Zone: (4?) 5 – 8
Propagation: seed, division, tip cuttings taken in June