tree

Silky Oak

The Story

Plant Bio

Grevillea robusta, commonly known as the silky oak, is a fast-growing evergreen tree native to the coastal and sub-coastal forests of eastern Australia. It develops a single straight trunk with dark grey, deeply furrowed bark and an open, pyramidal canopy that can reach heights of up to 40 metres in its natural habitat.

This species is distinguished by its deeply dissected, fern-like foliage and striking, horizontal golden-yellow to orange toothbrush-like flower racemes that appear in spring. It is highly valued as a robust rootstock for grafting delicate ornamental grevilleas due to its vigorous, adaptable root system.

Uses & Benefits:

Features deeply cut, fern-like foliage and brilliant golden-orange toothbrush flowers that create a dramatic seasonal display.

Functions as a highly durable, vigorous rootstock for grafting delicate ornamental Grevillea species.

Provides an abundant source of nectar for native honeyeaters, lorikeets, bees, butterflies, and flying foxes.

Essentials

At a Glance

Plant Type

Tree

Height

1575 inches

Width

591 inches

Light

Full Sun, Partial Sun

Zones

9, 10

Water

Low to moderate

Humidity

High to low

Lifespan

Long-lived

Native To

Eastern Australia

Toxicity

Skin irritant (contact dermatitis from sawdust/foliage)

Bloom period

Spring

In flower about 1 month of the year

Planting

How to Grow

Choose a spacious, full-sun position with well-drained soil to accommodate the tree's large ultimate size and extensive root system.
Dig a hole twice as wide as the root ball and of equal depth, ensuring the soil pH is mildly acidic to neutral.
Gently remove the plant from its pot, place it in the hole, backfill with native soil, and water in thoroughly to settle the roots.
Apply a layer of organic mulch around the base to retain moisture, keeping the mulch clear of the trunk to prevent collar rot.

Pro Tip

Never chop this tree back hard into bare, ancient wood to control its size; it lacks the ability to reliably shoot from old wood, and severe pruning will permanently disfigure or kill the specimen.

Keep It Thriving

Care Guide

Do

Water young trees regularly until established, particularly during dry spells.
Use only low-phosphorus, native-formulated fertilisers if feeding is necessary.
Ensure the planting site has excellent drainage to prevent root rot.

Don't

Do not plant close to house foundations, pipes, or in small courtyard gardens due to the aggressive root system.
Do not apply standard garden fertilisers containing high levels of phosphorus.
Do not prune heavily into old, leafless wood.

Seasonal Care Calendar

Task	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Fertilize
Mulch
Pest Check
Prune

Watch Out For

Pests & Diseases

Common Pests

Common Diseases

In the Garden

Landscape Uses & Companions

Landscape Uses

Large shade tree for parks and acreageWindbreak or shelterbelt plantingRevegetation of degraded alluvial or basaltic soils

Companion Plants

Doryanthes excelsa Lomandra longifolia Banksia integrifolia

Multiply

Propagation Methods

Good to Know

Common Questions

Silky Oak questions

What zones can Silky Oak grow in?

Silky Oak is hardy in USDA Zones 9–10. Inside that range it survives winter in the ground; outside it, grow it as an annual or a container plant you protect.

When does Silky Oak bloom?

Silky Oak typically blooms in spring through spring. Exact timing shifts a week or two with your zone — Sow's bloom calendar maps it to your garden.

Does Silky Oak need full sun?

Silky Oak does best in full sun to part shade. In hot climates, afternoon shade keeps blooms fresher longer.

Is Silky Oak drought tolerant?

Yes — once established (usually after the first full season), Silky Oak handles dry spells with minimal watering. Water deeply its first year to build the root system that makes that possible.