Pocket BotanistPlant guide
Late flowering thoroughwort.
Eupatorium serotinum
Pronounced yoo-pah-TOR-ee-um seh-RO-tin-um
Also known as fall boneset, late boneset, late eupatorium, late thoroughwort, late-flowering boneset, late-flowering thoroughwort, lateflowering thoroughwort
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This native perennial is a wonderful choice for supporting local pollinators in late summer. It grows in a sturdy, upright habit and produces clusters of tiny white flowers. You will find it thrives in moist, open areas.
At a glance
- Care level
- Easy
- Plant type
- Perennial
- Light
- Full sun to partial shade
- Indoor light
- Bright indirect
- Water
- Every 3 to 7 days
- Mature size
- 3 to 6 feet
- Growth rate
- Fast
- Hardiness
- USDA 4 to 9
- Bloom time
- Late summer to mid autumn
Care
Keep the soil consistently moist to mimic its natural wetland habitat. Once established it handles short dry spells, but watch for wilting during long droughts and water deeply if needed. It is very adaptable and requires little attention once established.
- Watering
- Keep the soil evenly moist at all times.
- Feeding
- Apply a balanced fertilizer once during the spring growth period.
- Pruning
- Cut the stems back to the ground in late winter or early spring.
- Repotting
- Repot only if the plant becomes root bound in its container.
- Soil
- Moist, fertile soil
- Soil pH
- Neutral to slightly acidic
- Temperature
- -25 to 35°C
- Humidity
- 40 to 80%
- Drought tolerance
- Moderate
- Lifespan
- Perennial, typically 5 to 10 years
- Deer and rabbits
- Moderate
Signs it needs repotting
- Roots growing out of the drainage holes.
- Water running straight through the pot without soaking in.
Safety
- People
- The plant contains pyrrolizidine alkaloids which can be harmful if consumed in large quantities.
- Pets
- This plant is generally considered toxic to cats and dogs if ingested.
- Children
- Keep children from chewing on the stems or leaves as they contain compounds that are not safe for ingestion.
- Contact allergens
- Handling the foliage may cause mild skin irritation in sensitive individuals.
- Airborne allergens
- The pollen can trigger seasonal allergies in susceptible people during the late summer bloom.
- Edibility
- This plant is not considered edible and may cause digestive upset if ingested.
How to identify it
- Opposite lance shaped leaves
- Rough textured foliage
- Clusters of white flower heads
- Sturdy upright branching stems
- Height
- 0.9 to 1.8m
- Spread
- 0.6 to 0.9m
- Leaves
- green, deciduous
- Flowers
- white, 0.5 to 1cm
Problems to watch for
- AphidsCommon
- Powdery MildewCommon
- CaterpillarsUncommon
- Leaf SpotUncommon
- Root RotUncommon
- RustUncommon
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Growing it
- Propagation
- seed, division, cuttings
- When to plant
- spring, autumn
- Overwintering
- Cut the stems back to the ground after the foliage dies back in late autumn. A light layer of mulch can help protect the crown during harsh winters.
- In containers
- It is generally too large and vigorous for typical containers, though it can grow in very large tubs.
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 moist, well drained soil.
Seed
- 1. Collect seeds in late autumn.
- 2. Sow seeds in pots or directly in the garden.
- 3. Provide a period of cold stratification for best germination.
Pair this plant with other late blooming perennials to ensure a continuous food source for pollinators until the first frost.
Grows well with
- Goldenrod · They bloom at the same time and create a beautiful contrast of white and yellow.
- New England Aster · This aster provides a lovely purple color that complements the white boneset flowers.
Similar species
- Common Boneset · It is closely related but blooms earlier and has leaves that clasp the stem.
Science
- Family
- Asteraceae
- Genus
- Eupatorium
- Order
- Asterales
- Class
- Magnoliopsida
- Native range
- Central and Eastern United States.
- Conservation
- This species is common and stable throughout its native range.
It naturally occurs in moist prairies, thickets, and along stream banks where it provides essential late season resources.
- Value to wildlife
- late season nectar source, supports diverse pollinators
- Pollinators
- bees, butterflies, moths
- Uses
- pollinator gardens, meadow plantings, naturalized areas
Through the year
Ecological indicators
- Salinity
- 2/9
- Soil reaction
- 5/9
- Light
- 7/9
- Temperature
- 6/9
- Moisture
- 6/9
- Nutrients
- 5/9
Taxonomy resolved against GBIF.
Questions people ask
- Is this plant invasive?
- It can spread readily by seed in ideal conditions but is generally considered a native wildflower rather than an invasive pest.
- Does it need staking?
- In rich soil, it can grow quite tall and may benefit from support if exposed to strong winds.
Where the name comes from
The genus name honors Mithridates Eupator, an ancient king who reportedly discovered medicinal properties in the group, while serotinum means late blooming.
Good to know
- It is often called late boneset because it blooms later than its relative Eupatorium perfoliatum.
- The tiny white flowers are arranged in flat topped clusters that act as landing pads for insects.
- It thrives in moist soils but is surprisingly adaptable to drier conditions once established.
Also in
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This guide was generated with AI on and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.