silkoak
Grevillea robusta · Proteaceae
silkoak (Grevillea robusta) is a perennial tree in the Proteaceae family. It is introduced to North America rather than native. USDA records it as hardy in zone 8 and warmer, down to about 17°F.
At a glance
| Type | tree USDA |
|---|---|
| Lifecycle | perennial USDA |
| Native status | introduced USDA |
| Mature height | 105 ft USDA |
| Light | full-sun USDA |
| Water need | medium USDA |
| Growth rate | rapid USDA |
| Soil pH | 5.3–7 USDA |
| Bloom | June–August USDA |
| Flower color | Yellow USDA |
| Hardiness zones | 8 and warmer USDA |
| Guild layer | canopy Derived |
| Nursery availability | Routinely Available USDA |
USDA quoted from the USDA PLANTS database · Derived computed by a fixed rule from those columns. No value on this page is estimated.
Growing conditions
It needs full sun. USDA rates it as having moderate water needs. Its drought tolerance is rated medium. It will not tolerate waterlogged soil — USDA rates its anaerobic tolerance as none. It is recorded on soils from pH 5.3 to 7 — a broad range that spans acidic through mildly alkaline ground. Its cold limit is zone 8.
Size and growth
At maturity it reaches about 105 ft, making it a large tree that will dominate its site. It grows quickly.
Bloom period
USDA records a bloom period of June through August. Flowers are yellow.
A flowering date, not a pollinator rating.
Foliage, flower and season
Summer foliage is green, fine in texture. Its flowers are conspicuous. Its fruit or seed heads are conspicuous, extending interest past flowering. Its active growth period is spring, summer, fall. Its winter foliage is dense, which makes it useful for year-round screening. USDA rates its lifespan as moderate.
What the site needs to provide
USDA records it across sites receiving 30 to 95 inches of annual precipitation. It needs at least 365 frost-free days to finish its season. It roots to at least 36 inches. Fertility requirement: medium.
Propagating it
Propagate it from seed, bare root and container stock. Seed needs cold stratification — a period of moist chilling — before it will germinate, so sow in autumn or chill it artificially before a spring sowing. Its seed spreads at a rapid rate. It does not spread vegetatively, so it will stay where you put it.
Resilience and wildlife
Its fire tolerance is rated low, and it can resprout after damage. Its growth form is recorded as single stem.
Role in a guild
Canopy. In a layered planting this is the tallest layer of a planting — it sets the light budget everything beneath it lives on. The layer is derived by a fixed rule from growth habit and mature height.
Tags
Related plants
Similar role and hardiness
- breadfruit Artocarpus altilis
- common bamboo Bambusa vulgaris
- gray sheoak Casuarina glauca
- coconut palm Cocos nucifera
- river redgum Eucalyptus camaldulensis
Where this data comes from
Every value on this page comes from the USDA PLANTS database record for symbol GRRO, or is computed from those values by a fixed rule. Nothing here is estimated or model-generated. Where USDA publishes no value, this page omits the claim rather than filling the gap.
- Quoted from USDA PLANTS: active growth period, Bloom, Bloom end, cold stratification, Drought tolerance, fall conspicuous, fertility requirement, fire tolerance, Flower color, flower conspicuous, foliage color, foliage porosity winter, foliage texture, frost free days min, fruit conspicuous, growth form, Growth rate, Hardiness zones, Lifecycle, lifespan, Light, Mature height, Minimum temperature, Native status, Nitrogen fixation, Nursery availability, precipitation max in, precipitation min in, propagation, resprout ability, root depth in, seed spread rate, Soil pH, Soil pH (upper), Tolerance of wet soil, Toxicity, Type, vegetative spread rate, Water need.
- Derived by a fixed rule from those columns: Guild layer.
Read our full data sources and methodology.
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