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Xeriscape Gardens

Pycnanthemum tenuifolium Care: Narrowleaf Mountain Mint


8 min read

Pycnanthemum tenuifolium is a hardy and adaptable plant that you can plant in your herb garden, along your garden borders, in a rain garden, and between rocks or as a xeriscaping plant. All parts of this plant, when crushed, have a strong fragrance of mint.

The dried leaves of this fragrant herbaceous perennial plant emit a mint-like aroma, and can be used as a food item. You can boil them to make mint tea! These are lovely native plants that hail from the rocky woods and open wet thickets of central and eastern North America. Their showy white flowers attract pollinators of all kinds: butterflies, honey bees, wasps, flies, beetles, and moths.

So let’s discuss this lovely plant, and how to grow it in your garden!

Quick Care Guide

Narrowleaf mountain mint close-up
Narrow leaf mountain mint makes for an amazing easy care ornamental. Source: milesizz
Common Name(s) Narrow-leaf mountain mint; slender mountain mint; common horsemint; Virginia thyme
Scientific NamePycnanthemum tenuifolium
FamilyLamiaceae
Height & Spread2-3 feet tall and 2-3 feet wide
LightFull sun to partial shade
SoilShallow, rocky, well-draining
WaterLow to medium
Pests & DiseasesVirtually free of pests and diseases

All About Narrowleaf Mountain Mint

The slender mountain mint is part of the mountain mint plant family (Lamiaceae). Also known as narrow-leaf mountain mint, Pycnanthemum tenuifolium features extremely narrow, slender leaves that separate it from other mountain mint species, all of which are native to North America.

This herbaceous perennial plant is native to every county of central and southern Illinois, and most of eastern North America. It is also found growing in open wet thickets, rocky woods, woodland openings, moist thickets and meadows, limestone glades, acid gravel seeps, and abandoned fields. It’s perfect for native plant gardens and any rain garden in that range.

Pycnanthemum tenuifolium is an erect and tall herbaceous perennial that blooms clusters of tiny, white flowers, and has narrow, needle-like silvery foliage and slender, hairless stems. These plants frequently branch into a shrub-like or bushy formation.

Mountain mint spreads through the ground via rhizomes that allow it to appear as a striking mass of white flowers in late summer. These plants are a favorite among animals and insects – native bees love to swarm the mildly minty fragrant white flowers.

Pycnanthemum tenuifolium Care

Pycnanthemum tenuifolium flowers
Pycnanthemum tenuifolium is a wonderful low-growing ground cover plant. Source: FritzFlohrReynolds

Now that we’ve discussed the botanical characteristics of this wonderful plant, let’s discuss its care and cultivation for that lovely mint like aroma. You may find your mountain mint is the happiest plant in your garden.

Light & Temperature

P. tenuifolium needs full sun, but can also survive in partially shaded areas. USDA Plant Hardiness Zones 4 to 8 are ideal for this plant, as it is native to rocky woods within these zones. You can stretch it outside these zones with proper care, however. As long as your plant is established in an area or container and isn’t exposed to consistent temperatures below 15°F, you’re good!

Heat is no issue for this plant, as it grows wild in areas of the south that are very hot in summer. However, in full sun give it some afernoon shade. In its hardiness range, the plant is an herbaceous perennial. Leaves will die back in winter leaving its lovely seeding flower heads, and return lush and green the following spring from its roots.

Water & Humidity

This plant needs a low to medium amount of water. Let the soil dry out completely between watering rounds, or water it with drip irrigation or soaker hoses. If you’re setting an automatic irrigation system, don’t worry about watering mountain mint much after it’s established.

It has some tolerance to drought, but may need regular water once per week in the dead heat of summer, especially in full sun. Don’t worry about watering in rainier times or temperate times. And varying humidity percentages are appropriate for growing this plant. If you live in a dry area, consider planting your mountain mint in a rain garden to give it the water it needs.

Pycnanthemum Tenuifolium Soil

This mint family plant prefers moist to slightly dry conditions and well-draining soil. Many different types are suitable as long as they retain some water and nutrients, but drain well. This plant often grows in rich, loamy, and slightly rocky soil. Open wet thickets, meadows and bogs are where you find the plant in the wild. Consider these conditions when you’re building soil for your plant. Soil pH of 6.8 is optimal, too.

Fertilizing Slender Mountain Mint

This plant has no special fertilizing needs, it’ll grow without additional fertility. In fact, you might find your plant doesn’t perform as well when supplemental nutrients are added, especially in its native range. A light dressing of compost annually is enough to keep it happy.

Pycnanthemum tenuifolium Propagation

Propagate your plant via divisions and seeds. For division, cut off the tips of your plant in June, divide a clump of your plant in late fall or early spring and use stainless steel pruning shears to divide the shallow root system.

For propagation via seeds, collect the seeds after the first few frosts. If the seeds are ripe, they will fall out when you bend over the stem and shake it. Store these in a sealed, refrigerated container and plant them in seed starting trays 6 to 8 weeks before the last frost. Simply tamp them into the surface of the soil. Harden them off and plant them in your preferred area or container outdoors when spring has arrived.

Pruning Mountain Mint

Mountain mint features extremely narrow leaves that may or may not need pruning. To keep your plant from spreading all across your garden, you can occasionally divide it from the roots and either transplant into a new area, or toss into your compost pile. You can also control its spread through deadheading spent flowers.

Remove dead and diseased leaves as needed. There’s no need to prune otherwise. Leave the flowers and stalks through the cold months for overwintering native insects and pollinators.

Troubleshooting

Pycnanthemum tenuifolium, is a low maintenance plant. However, it can face some growing problems.

Growing Problems

Make sure that you don’t over-water your plant or keep it away from sunlight as your plant needs full sun and dry to lightly moist soil to thrive. If you do this or plant it in compacted soil, you may find fungal rusts are more likely to develop.

Another issue that can arise is when your mint is planted in an area and doesn’t receive enough moisture. In this case, you’ll notice the bottom leaves yellowing and falling off. Increase water frequency in this case.

Pests & Diseases

This plant is virtually pest-free, and is highly deer-resistant and rabbit-resistant. However it can succumb to rust in situations where the fungus that causes the disease is present, and when the plant is placed in conditions it is not suited to growing in. If you notice rust-colored spots appearing on the undersides of leaves in spring, you’re dealing with rust.

There is no cure for rust. Simply remove damaged foliage as it crops up, and ensure your plant is in correct light and soil conditions. Also never water the foliage of the plant and only apply irrigation at its base. Plants that are overtaken by rust should be removed and disposed of, but most of the time it doesn’t come to that.

Frequently Asked Questions

Q: How to tell if my narrow narrow-leaf mountain mint is thirsty for water?

A: The leaves of your plant might develop a yellowish tinge during prolonged periods of drought, especiall in hot summers and full sun areas. This is your sign to water your plant.

Q: Does slender mountain mint smell like mint?

A: This plant features extremely narrow leaves of the plant emit a slight mint-like aroma and can be boiled to make mint tea.

Q: Is slender mountain mint invasive?

A: While it can be aggressive in optimal conditions, it’s not invasive. Mountain mints are native plants.

Q: Where to plant Slender Mountain mint?

A: Plant it in rich, well-draining soil, and full sun to partial shade.

Q: Should I cut back mountain mint?

A: While you can cut it back in late fall or early winter, if you don’t you’ll save some habitat for overwintering insects and pollinators. This is also a way to control its spread via self-seeding.

Q: Can you divide mountain mint?

A: You can! Carefully divide it as it emerges in early spring.

Q: How do you collect mountain mint seeds?

A: Wait for the first few frosts to pass. Then shake the stems of the plant and collect any of the seeds that fall to the earth. You can place some cardboard or paper below the plant while you do this to catch any that fall.

Q: What does mountain mint look like in the winter?

A: Even in winter, this plant puts on a lovely display. The seed heads become a stark gray with a dark black center, and the brown branches are exposed without spring foliage. Winter color is definitely achievable with P. tenuifolium.

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