African redwood (kosso) Hagenia abyssinica
African redwood (kosso) (Hagenia abyssinica) is an evergreen perennial tree in the Rosaceae family, native to East African high mountains (2,400–3,600 m). It grows 10–20 m (33–66 ft) tall and 8–14 m (26–46 ft) wide, wants full sun and moderate water, and is hardy to about -2 °C (28 °F). Space plants about 10 m (33 ft) apart.
Plan African redwood (kosso) in your garden →
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African redwood (kosso) at a glance
| Type | Perennial tree, evergreen |
|---|---|
| Family | Rosaceae |
| Mature height | 10–20 m (33–66 ft) |
| Mature spread | 8–14 m (26–46 ft) |
| Spacing | 10 m (33 ft) 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 | 5–7 |
| Cold hardiness | About -2 °C (28 °F) once established (roughly USDA zone 9) |
| Heat stress | Likely above about 28 °C (82 °F) |
| Flowering | about 417–626 weeks after planting, for 6–10 weeks |
| Wind tolerance | Moderate |
| Pollinator value | Moderate |
| Edible | Not grown as food |
| Native to | East African high mountains (2,400–3,600 m) |
| Common in gardens of | 🇪🇹 Ethiopia, 🇰🇪 Kenya |
Is African redwood (kosso) toxic?
- People: moderately toxic
- Cats: moderately toxic
- Dogs: moderately toxic
- Parts: flowers
Female flowers were a traditional (and toxic) tapeworm remedy.
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 African redwood (kosso)
Good neighbours
- good With Garlic chives: Gardeners plant garlic chives among roses to deter aphids and black spot; the evidence is weak and mostly anecdotal. Evidence D
Questions about African redwood (kosso)
- How far apart should I plant African redwood (kosso)?
- About 10 m (33 ft) apart, centre to centre. A mature plant spreads 8–14 m (26–46 ft).
- Does African redwood (kosso) need full sun?
- Full sun: at least 5 hours of direct sun a day.
- How much water does African redwood (kosso) need?
- Moderate water. Drought tolerance is low and waterlogging tolerance none.
- How cold-hardy is African redwood (kosso)?
- It tolerates about -2 °C (28 °F) once established, roughly USDA zone 9.
- When does African redwood (kosso) flower?
- About 417–626 weeks after planting, for 6–10 weeks.
- Is African redwood (kosso) poisonous to cats and dogs?
- For cats it is moderately toxic; for dogs moderately toxic; for people moderately toxic. Female flowers were a traditional (and toxic) tapeworm remedy.
- What grows well with African redwood (kosso)?
- Gardeners plant garlic chives among roses to deter aphids and black spot; the evidence is weak and mostly anecdotal.
Sources and evidence
Evidence grade C (C: plausible, mixed evidence).
- PROTA4U: Plant Resources of Tropical Africa, PROTA Foundation, Wageningen
- Plants of the World Online (taxonomy, native range), Royal Botanic Gardens, Kew
Notes and assumptions
- Huge drooping pink-red flower panicles on female trees; a tree of the Afromontane forest edge.
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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