Mountain mint
Pycnanthemum muticum · Lamiaceae
The leaves around each small flower head look as if they have been dusted with silver, so the whole plant shimmers in summer. In trials it attracts more pollinators than almost any other plant.
- Size
- 3 ft tall, 3 ft wide
- Zones
- 4 to 8
- Light
- Full sun to part sun
- Flowers
- Early July to early September
- Pets
- No toxicity recorded
- Job in a bed
- Drift
A bed built around mountain mint
The planner designed this bed around mountain mint when this page was made: a 12 × 6 ft (3.7 × 1.8 m) naturalistic planting in zone 6, full sun. It chose the other plants from the 966 that suit those conditions, and says below why mountain mint stands where it does.
The plants
- 1 Mountain mint × 3, white
- 2 Winter heath × 9, pink
- 3 Horned violet × 7, purple
- 4 Brown-eyed Susan × 3, yellow
- 5 Silver sage × 1, silver leaves
- 6 Purple moor grass 'Variegata' × 4, purple
- 7 Ornamental onion 'Purple Sensation' × 5, purple
- 8 Daffodil 'Tete-a-Tete' × 12, yellow
Why this plant
- The only dense clusters. The others are bells, daisies, airy sprays and others. Shape reads at a distance, where colours blur.
- The only white. White sits between stronger colours and calms them.
Why here
- Anchors a back corner. At 3 ft it is one of the taller plants here, and the tallest close the ends of the bed, where they stand in front of nothing.
- A step in the back row. Next to ornamental onion 'Purple Sensation' (2½ ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- 3 plants in one group. Massed, one kind reads as a single shape. Scattered, it would look spotty.
Why now
- In flower for 10 weeks. From early July to early September.
- Fills a gap. For one of those weeks nothing else on the plan is in flower.
Planned as a naturalistic planting: low grasses and groundcovers, the matrix, make up 48% of the planted ground. The flowering year starts with winter heath in late January and ends with brown-eyed Susan in early October. The scheme leans cool (pink and purple) and uses yellow for warmth, with white to calm things between them.
The planner's own design check: 12 Excellent, 5 Good. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where mountain mint goes in a border
At 3 ft it belongs in the middle of a bed. In the planner's ten height classes it is medium tall (2½ to 3 ft).
Its job: drift. Planted in a small group of three or five, and repeated further along in the other number.
Use it as a cool, silvery filler between brighter flowers. It spreads by runners like its mint relatives, though the shallow roots are easy to pull. The leaves smell of spearmint.
- Pollinator gardens
- A silver haze to set off stronger colours
- Naturalising in moist soil
What to plant with mountain mint
Plants recorded as good partners for it, and what each pairing does:
- Purple coneflower: in flower together for 10 weeks, from early July.
- Switchgrass 'Shenandoah': its green leaves are a setting for the flowers, before and after.
- Joe Pye weed 'Little Joe': in flower together for seven weeks, from late July; bold leaves against its medium ones; happy in the same moist soil.
Questions about mountain mint
Does mountain mint need sun or shade?
Mountain mint grows in full sun (6 or more hours of direct sun a day) and part sun (4 to 6 hours of sun, including some afternoon sun).
It wants soil that stays evenly moist, of average fertility, and a good soak in dry spells.
What zones does mountain mint grow in?
USDA zones 4 to 8. It is hardy to zone 4, which means it survives winter nights down to about −20 °F (−29 °C).
Above zone 8 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does mountain mint flower in my zone?
In zone 5 it flowers early July to early September. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 4 | Mid July to early September |
|---|---|
| Zone 5 | Early July to early September |
| Zone 6 | Early July to early September |
| Zone 7 | Late June to early September |
| Zone 8 | Late June to early September |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should mountain mint be planted?
24 in (60 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 3 ft (90 cm), so a group knits into one patch.
It grows 3 ft (90 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many mountain mint plants do I need?
At 24 in apart, set out in staggered rows:
- 3 to fill 10 square feet (about 1 m²)
- 6 for a single row 10 ft (3 m) long
- 10 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as a group of three or five, with a second group further along in the other number.
In the bed above, the planner used three in one group.
Is mountain mint poisonous to dogs and cats?
No toxicity is recorded for dogs, cats, horses or people, according to NC State Extension.
"Not toxic" is not "edible": a pet that eats a lot of any plant can be sick.
Do deer eat mountain mint?
They may. NC State does not list it as resistant to deer or rabbits. Where they visit, protect it, or plant it among ones they avoid.
Will mountain mint spread?
It spreads sideways, by runners or roots; the risk of it taking over is moderate. Spreads by underground runners and can crowd its neighbours. Dig out the edges or divide every 2 to 3 years.
What flowers after mountain mint?
Mountain mint is over by early September. These start as it finishes and carry the same spot on, so it never goes flat:
- Garden chrysanthemum: from mid September to late October, 24 in tall, to stand in front of it and cover its fading stems.
- Blue mistflower: from late August to mid October, 2½ ft tall.
- Blue-stemmed goldenrod: from early September to mid October, 2½ ft tall.
What does mountain mint look like in winter?
Mountain mint dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.
Is mountain mint good for bees and butterflies?
Mountain mint is visited by pollinators, bees and butterflies.
It is a host plant: the caterpillars of wavy-lined emerald feed on its leaves. A butterfly can only lay its eggs on its host plants, so these do more for it than any nectar flower.
It is native to the United States.
More Pycnanthemum
- Slender mountain mint Pycnanthemum tenuifolium
In these guides
- Pet-safe plants for a sunny border
- Native perennials for pollinators
- Plants for butterflies
- Plants for bees
- Plants for a white garden
- Host plants for the wavy-lined emerald
Every fact on record
- Type
- Perennial
- Size
- 3 ft (90 cm) tall, 3 ft (90 cm) wide
- Plant
- 24 in (60 cm) apart
- Height class
- Medium tall (2½ to 3 ft)
- Place in the bed
- Middle
- Flowers
- Early July to early September; dense clusters; white
- Leaves
- Medium texture, herbaceous; green
- Shape
- Upright, spreading
- Hardy in
- USDA zones 4 to 8
- Light
- Full sun, part sun
- Soil
- Average, evenly moist
- Water
- Moderate
- Feeding
- None needed
- Family
- Lamiaceae
- Comes from
- Eastern Central & Eastern U.S.A
- Attracts
- Pollinators, bees, butterflies
- Host plant for
- Wavy-lined emerald
Checked against NC State Extension. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.