Plant of the Month for October, 2014

Pycnanthemum tenuifolium header
Pycnanthemum tenuifolium

 (pik-NAN-thee-mum ten-yoo-ih-FOH-lee-um)

General Information:

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 seems fairly well behaved and is an insect/butterfly magnet. It is native to the north-east part of North America, including Ontario.

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Pycnanthemum tenuifolium; photo by Robert Pavlis

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.

Pycnanthemum tenuifolium closeup

Pycnanthemum tenuifolium; photo by Robert Pavlis

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



Light: full sun to part shade

Soil: variable

Water: dry to wet

USDA Hardiness Zone: (4?) 5 – 8

Propagation: seed, division, tip cuttings taken in June

Seedex availability (ORG&HPS annual Seed Exchange): rarely

Requires light or the small seeds should be surface sown. See
Sow @ 20°C. Seed germinates within 3 months.
Robert Pavlis