Silkoak Grevillea robusta
Silkoak is an introduced perennial tree, found in Hawaii, the lower 48 states, and Puerto Rico. It grows to 105 ft and blooms Jul in part shade – shade, with brown fruit.
More about this plant
Grevillea robusta, commonly known as the southern silky oak, silk oak or silky oak, silver oak or Australian silver oak, is a species of flowering plant in the family Proteaceae. Despite its common names, it is unrelated to true oaks, which belong to the family Fagaceae. Grevillea robusta is a tree, and is the largest species in its genus. It is a native of eastern coastal Australia, growing in riverine, subtropical and dry rainforest environments. Wikipedia →
Silkoak is flagged invasive in the U.S. These natives fill a similar niche — same growth habit, bloom season, height, and region — so you keep the look and feed local wildlife instead of spreading a problem.
Growing & care
USDA PLANTS · TRY- Sun
- Part shade – shade
- Soil & moisture
- Medium moisture
- Soil pH
- 5.3–7
- Fertility need
- Medium
- Adapts to
- Coarse (sandy), Medium (loam), Fine (clay)
- Hardiness
- USDA zone 9+
- Height
- 105 ft
- Mature width
- ≈ 35 ft wide wild/forest-grown — open-grown specimens spread wider
- Spacing
- 7–12 ft apart from USDA planting density
- Spread
- None — clumping
- Growth rate
- Rapid
- Growth form
- Single stem
- Lifespan
- Perennial · moderate
- Foliage
- Evergreen broadleaf · fine texture
- Active growth
- Spring through autumn
- Fruit
- Brown persists into winter
- Propagate by
- Seed, Bare root, Container
- Seed starting
- Needs cold stratification a cold-moist spell before it germinates
- Seeds ripen
- Autumn – Winter seed-collection / harvest window
- In the trade
- Routinely available
- Resprouts if cut
- Yes regrows after top-kill
Sow timing keys off your local last- and first-frost dates.
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts Documented caterpillar host
Recorded feeding on Grevillea in North America, including:
✦ Bees 2 bee visitors
2 native & managed bee species are documented visiting Silkoak :
Wildlife & visitors 21 birds
Open records of who else uses Silkoak — a generalist food-web signal, kept separate from the keystone Ecological Value.
Recorded eaten by 21 birds species (fruit, seed, browse) — the most-recorded:
Related plants
More Grevillea →
How we know this (3) Methods & honest limits
We read each species’ measured specific leaf area (leaf area per unit dry weight) from the Global Spectrum dataset and band it: thin & fast (high SLA), medium, or thick & tough (low SLA). The global median is about 10 mm²/mg.
Honest limits: A species-mean from pooled measurements — individual plants vary with light and site. A broad strategy signal, not a precise per-plant figure.
A recorded categorical fact: each species is tagged C3 (standard), C4 (heat/water-efficient) or CAM (succulent, night-time CO₂ uptake) — or a facultative combination. We only show a trait card for the noteworthy C4/CAM cases; C3 is the unremarkable majority, kept in the data but not surfaced as a card.
We take the plant’s U.S. county range and look up each county’s long-term climate, then summarise: native rainfall = the median annual rainfall across its counties; heat tolerance = the warm end (90th percentile) of average temperature across its range (mirroring how our cold-hardiness floor uses an extreme). Counties + medians blunt the roadside/observer bias that makes point-level climate unreliable. Needs at least five placeable counties.
Honest limits: A realized, sampling-biased niche (where it has been recorded, not its physiological optimum), and county climate is coarse — large Western counties span deserts and mountains. Derived guide, never a measured fact.
Sources for this entry (35) Open & cited
Cite this page Open data, please attribute
PlantKey’s data is open under CC BY-SA 4.0 — free to reuse and adapt, with attribution and the same licence. Photos keep their own per-image licence + credit (see Sources above).
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