Siamese cycad Cycas siamensis
Siamese cycad (Cycas siamensis) is an evergreen perennial shrub in the Cycadaceae family, native to Thailand, Myanmar, Laos, Cambodia and Vietnam (dry dipterocarp forest). It grows 80 cm–2 m (31 in–6.6 ft) tall and 1.5–2.5 m (4.9–8.2 ft) wide, wants full sun and low water, and is hardy to about 0 °C (32 °F). Space plants about 2 m (6.6 ft) apart.
Plan Siamese cycad in your garden →
Free. Draw your beds, then watch it grow through the year in 2D and 3D.
Siamese cycad at a glance
| Type | Perennial shrub, evergreen |
|---|---|
| Family | Cycadaceae |
| Mature height | 80 cm–2 m (31 in–6.6 ft) |
| Mature spread | 1.5–2.5 m (4.9–8.2 ft) |
| Spacing | 2 m (6.6 ft) centre to centre |
| Sun | Full sun, at least 5 h of direct sun a day |
| Water | Low; drought tolerance high, waterlogging tolerance none |
| Soil pH | 5.5–7.5 |
| Cold hardiness | About 0 °C (32 °F) once established (roughly USDA zone 10) |
| Heat stress | Likely above about 42 °C (108 °F) |
| Flowering | from about April for 4–9 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Moderate |
| Pollinator value | None |
| Edible | Not grown as food |
| Native to | Thailand, Myanmar, Laos, Cambodia and Vietnam (dry dipterocarp forest) |
| Common in gardens of | 🇹🇭 Thailand |
Is Siamese cycad toxic?
- People: severely toxic
- Cats: severely toxic
- Dogs: severely toxic
- Parts: seeds, all parts
Cycasin: all parts poisonous.
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 Siamese cycad
No well-documented helpful pairing. Group it with plants that like full sun and low water.
See Siamese cycad in a botanical garden
It grows in these sample gardens, which you can walk through in 3D:
- Nong Nooch Tropical Botanical Garden (10 plants)
- Fairy Lake Botanical Garden (5 plants)
Questions about Siamese cycad
- How far apart should I plant Siamese cycad?
- About 2 m (6.6 ft) apart, centre to centre. A mature plant spreads 1.5–2.5 m (4.9–8.2 ft).
- Does Siamese cycad need full sun?
- Full sun: at least 5 hours of direct sun a day.
- How much water does Siamese cycad need?
- Low water. Drought tolerance is high and waterlogging tolerance none.
- How cold-hardy is Siamese cycad?
- It tolerates about 0 °C (32 °F) once established, roughly USDA zone 10.
- When does Siamese cycad flower?
- From about April for 4–9 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Siamese cycad poisonous to cats and dogs?
- For cats it is severely toxic; for dogs severely toxic; for people severely toxic. Cycasin: all parts poisonous.
- What grows well with Siamese cycad?
- There is no well-documented companion pairing for Siamese cycad. Group it with plants that like the same sun (full sun) and water (low).
Sources and evidence
Evidence grade B (B: extension service or peer-reviewed).
- Plants of the World Online (taxonomy, native range), Royal Botanic Gardens, Kew
- IUCN Red List of Threatened Species, IUCN
- Nong Nooch Tropical Botanical Garden: palm and cycad collections, Nong Nooch Tropical Botanical Garden
Notes and assumptions
- Swollen, partly underground trunk; deciduous in the dry season and fire-adapted. Nong Nooch holds one of the world's largest cycad collections.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Sago cycad Cycas revoluta
- Fairy Lake cycad Cycas fairylakea
- Bigleaf hydrangea Hydrangea macrophylla
- Rhododendron Rhododendron
- Boxwood Buxus sempervirens
- Oleander Nerium oleander
- Common ninebark Physocarpus opulifolius
- Camellia Camellia japonica