Floss flower (ageratum) Ageratum houstonianum
Floss flower (ageratum) (Ageratum houstonianum) is an annual flowering plant in the Asteraceae family, native to Mexico and Central America. It grows 20–50 cm (8–20 in) tall and 20–40 cm (8–16 in) wide, wants full sun and moderate water, and is hardy to about 0 °C (32 °F). Space plants about 25 cm (10 in) apart.
Plan Floss flower (ageratum) in your garden →
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Floss flower (ageratum) at a glance
| Type | Annual flowering plant |
|---|---|
| Family | Asteraceae |
| Mature height | 20–50 cm (8–20 in) |
| Mature spread | 20–40 cm (8–16 in) |
| Spacing | 25 cm (10 in) centre to centre |
| Sun | Full sun, at least 5 h of direct sun a day |
| Water | Moderate; drought tolerance low, waterlogging tolerance none |
| Soil pH | 6–7.5 |
| Cold hardiness | About 0 °C (32 °F) once established (roughly USDA zone 10) |
| Heat stress | Likely above about 32 °C (90 °F) |
| Flowering | about 6–10 weeks after planting, for 13–21 weeks |
| Days to maturity | About 70 days from planting |
| Wind tolerance | Low |
| Pollinator value | High |
| Edible | Not grown as food |
| Native to | Mexico and Central America |
| Common in gardens of | 🇲🇽 Mexico, 🇺🇸 United States |
Is Floss flower (ageratum) toxic?
- People: mildly toxic
- Cats: not well documented
- Dogs: not well documented
- Parts: foliage, flowers
Contains pyrrolizidine alkaloids that are liver-toxic to livestock; risk from garden contact is low but pet data are lacking.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Floss flower (ageratum)
No well-documented helpful pairing. Group it with plants that like full sun and moderate water.
See Floss flower (ageratum) in a botanical garden
It grows in this sample garden, which you can walk through in 3D:
- Longwood Gardens (20 plants)
Questions about Floss flower (ageratum)
- How far apart should I plant Floss flower (ageratum)?
- About 25 cm (10 in) apart, centre to centre. A mature plant spreads 20–40 cm (8–16 in).
- Does Floss flower (ageratum) need full sun?
- Full sun: at least 5 hours of direct sun a day.
- How much water does Floss flower (ageratum) need?
- Moderate water. Drought tolerance is low and waterlogging tolerance none.
- How cold-hardy is Floss flower (ageratum)?
- It tolerates about 0 °C (32 °F) once established, roughly USDA zone 10. As an annual it is usually planted out after the last frost.
- When does Floss flower (ageratum) flower?
- About 6–10 weeks after planting, for 13–21 weeks.
- Is Floss flower (ageratum) poisonous to cats and dogs?
- For cats it is not well documented; for dogs not well documented; for people mildly toxic. Contains pyrrolizidine alkaloids that are liver-toxic to livestock; risk from garden contact is low but pet data are lacking.
- What grows well with Floss flower (ageratum)?
- There is no well-documented companion pairing for Floss flower (ageratum). Group it with plants that like the same sun (full sun) and water (moderate).
Sources and evidence
Evidence grade C (C: plausible, mixed evidence).
- RHS Plant Finder, Royal Horticultural Society
- Extension Gardener Plant Toolbox, NC State Extension
Notes and assumptions
- Typical garden-form values; cultivars and local conditions differ.
- Tender perennial in the tropics, grown as an annual in most gardens; counted from transplant.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
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