Yes, the leaves have a strong, musky, and rather unpleasant odor when touched or crushed.

It can be aggressive in some garden settings, so keep an eye on it.

Plant guide

Black horehound.

Ballota nigra

Pronounced bal-LO-ta NY-gra

Also known as Black Horehound

Black horehound is a hardy perennial herb often found in disturbed soil or near hedgerows. It has a distinct, somewhat pungent scent when the leaves are crushed. You will find it produces small, purplish flowers in dense clusters along its stems.

At a glance

Care level: Easy
Plant type: Perennial herb
Light: Full sun to partial shade
Indoor light: Bright indirect
Water: Every 7 to 14 days
Mature size: 3 feet
Growth rate: Medium
Hardiness: USDA 5 to 9
Bloom time: Mid to late summer

Care

This plant thrives in well-drained soil and prefers a spot with plenty of airflow. Keep an eye out for aphids or powdery mildew if the air becomes too stagnant. It is quite resilient, so just make sure it does not sit in waterlogged soil.

Watering: Allow the top inch of soil to dry out between waterings.
Feeding: Apply a balanced liquid fertilizer sparingly during the active growing season.
Pruning: Trim back spent flower stalks to encourage a tidy shape and potential second bloom.
Repotting: Move to a slightly larger container once the roots begin to circle the pot.
Soil: Well-draining, loamy soil
Soil pH: 6.0 to 7.5
Temperature: -15 to 35°C
Humidity: 30 to 70%
Drought tolerance: High
Lifespan: Perennial, typically 3 to 5 years.
Deer and rabbits: High

Signs it needs repotting

Roots growing out of the drainage holes.
Water sitting on the surface of the soil.
Stunted growth during the active season.

Safety

People: It is not considered toxic, but it is not meant for human consumption.
Pets: This plant is generally considered non-toxic to cats and dogs.
Children: Keep children away from the plant as the strong, unpleasant odor and hairy texture are unappealing and potentially irritating.
Contact allergens: The foliage can cause mild skin irritation in sensitive individuals due to fine hairs.
Airborne allergens: The pollen may trigger mild reactions in those with severe seasonal allergies.
Edibility: This plant is generally considered inedible and has a very unpleasant odor when crushed.

How to identify it

Opposite, ovate, wrinkled leaves
Dense clusters of purplish flowers
Square stems typical of mint family
Strong, unpleasant odor when bruised

Height: 0.45 to 0.9m
Spread: 0.3 to 0.6m
Leaves: dark green, greyish green, semi-evergreen
Flowers: purplish pink, white, 0.5 to 1.5cm

Problems to watch for

Powdery mildew · A fungal infection that appears as white dust on leaves during humid weather.
Aphids · Small insects that cluster on new growth and suck plant sap.

By symptom

Plant problems by symptom

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Growing it

Propagation: seed, division, cuttings
When to plant: spring, autumn
Overwintering: Cut back dead stems in late winter to encourage fresh spring growth. No special protection is needed in temperate climates.
In containers: It grows well in containers at least 30 cm deep, though it is better suited for the open garden.

Division

1. Dig up the clump in early spring.
2. Use a sharp spade to divide the root ball into smaller sections.
3. Replant immediately in well draining soil.

Pair this plant with other drought tolerant herbs to create a low maintenance pollinator patch.

Grows well with

Lavender · They share similar requirements for sun and well drained soil.
Sage · Both plants enjoy similar Mediterranean style growing conditions.

Similar species

White Horehound · It has a similar growth habit but lacks the unpleasant odor.

Science

Family: Lamiaceae
Genus: Ballota
Order: Lamiales
Class: Magnoliopsida
Native range: Europe, North Africa, and parts of Western Asia.
Conservation: It is a common, widespread weed in many regions and is not of conservation concern.

It thrives in nitrogen rich, disturbed soils where it outcompetes other species for space.

Value to wildlife: nectar source
Pollinators: bees
Uses: pollinator garden, wildlife habitat, ground cover

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 2/9
Soil reaction: 6/9
Light: 7/9
Temperature: 5/9
Moisture: 4/9
Nutrients: 7/9

Taxonomy resolved against GBIF.

Questions people ask

Does it smell bad?: Yes, the leaves have a strong, musky, and rather unpleasant odor when touched or crushed.
Is it invasive?: It can be aggressive in some garden settings, so keep an eye on it.

Where the name comes from

Ballota comes from the Greek word for a type of plant, while nigra refers to the dark foliage color.

Good to know

The name nigra refers to the dark color the leaves turn when dried.
It is often found growing in disturbed soil near old buildings or roadsides.
The flowers are small but produced in dense, whorled clusters.

Also in

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This guide was generated with AI on October 19, 2026 and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.