Red silky oak

Sun

Full sun; tolerates light shade but flowers less freely.

Water

Water regularly while establishing, then deeply during extended dry spells. Let the soil drain and begin to dry between waterings.

Soil

Well-drained, preferably acidic to neutral sandy or gravelly soil. Avoid waterlogged ground, strongly alkaline soil and phosphorus-rich amendments.

Height

6-20 ft (1.8-6 m)

Spread

6-12 ft (1.8-3.7 m)

Flowers

Red, occasionally cream or white, in large brush-like clusters; strongest from late winter through spring, with intermittent flowering through the year in frost-free climates.

Foliage

Evergreen. Leathery, deeply divided green leaves with narrow lobes and pale, silky undersides.

Growth

Moderate to fast in warm conditions.

Care needed

Medium

• Pollinators
• Drought tolerant
• Heat tolerant
• Wildlife
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Hard

Toughness

Needs looking after

Pick your zone, country, light and whether you have pets.

1. Planting day

   1.6 ft (0.5 m)

2. After 1 year

   4 ft (1.3 m)

3. After 2 years

   7 ft (2.2 m)

4. After 3 years

   10 ft (3.1 m)

5. After 5 years

   13 ft (3.9 m)

   full size

About 4 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Toxic

Native to

Australia

Growth rate

Fast

• Plant after frost danger has passed, keeping the root ball level with the surrounding soil.
• Water deeply through the first growing season; avoid frequent watering that keeps the roots wet.
• Feed sparingly with a low-phosphorus fertilizer labelled for Australian native plants; avoid bone meal and general-purpose high-phosphorus feeds.
• Apply a loose organic mulch, keeping it clear of the trunk.
• Protect young plants from frost; move container plants into bright, frost-free shelter before freezing weather.
• Use a freely draining potting mix for containers and never leave the pot standing in water.

Pruning. Lightly shorten shoots after the main flowering flush to encourage branching, and remove dead or damaged growth as needed. Avoid cutting hard into old, bare wood, which may not regrow reliably.

Spring

Plant once frost risk has passed, choosing a sunny, freely draining position.

Spring

Apply a small amount of low-phosphorus native-plant fertilizer if growth is weak.

Late spring

Lightly prune after the main flowering flush, retaining leafy growth below each cut.

Summer

Check new plantings and containers regularly; water deeply when needed without keeping the roots saturated.

Autumn

Move container plants under bright, frost-free cover before the first frost.

Winter

Keep sheltered container plants on the dry side, but do not let the root ball dry out completely.

• Use as a flowering specimen in a sunny Australian native garden, with lower shrubs beneath its canopy.
• Plant in a loose wildlife screen with bottlebrushes and other grevilleas to provide nectar and cover.
• Combine with silver foliage and ornamental grasses in a warm, well-drained gravel garden.
• Grow in a large container on a sunny terrace where it can be moved into winter shelter.

Garden styles it suits: Australian native, Wildlife garden, Coastal, Dry gravel garden, Mediterranean and Architectural minimal.

Plant it with: Kangaroo paw, Coastal rosemary, Waxflower, Bottlebrush, Mat rush and Dwarf banksia.

Wildlife: Flowers provide nectar for honeyeaters in Australia and other nectar-feeding birds where grown, as well as visiting insects. Dense branches offer shelter for small birds.

• Root rot: wet soil can cause sudden decline or death; improve drainage, reduce watering and avoid planting in depressions.
• Phosphorus toxicity: leaf yellowing, scorched tips and poor growth can follow unsuitable fertilizer; stop feeding and use only low-phosphorus products.
• Scale insects: inspect stems and leaf undersides; treat small infestations with horticultural oil according to the label, avoiding hot weather and open flowers.
• Frost damage: young shoots may blacken after freezing; protect plants before frost and wait until spring growth begins before removing damaged wood.

Leaves and flowers can cause allergic contact dermatitis in people; wear gloves when pruning, especially if you have sensitive skin. The flowers and nectar contain cyanogenic compounds and should not be eaten. Poisoning risk in cats, dogs and horses is poorly documented, so do not treat it as a known-safe browsing plant.

Where it spreads. Invasive in eastern and southeastern Madagascar, where it forms extensive stands and displaces native vegetation. Avoid planting near natural areas there.

• Silky oak (Grevillea robusta)

  A much larger tree with finer, fern-like leaves and golden-orange flowers arranged in one-sided combs rather than dense red clusters.

• Scarlet grevillea (Grevillea beadleana)

  Usually a lower, spreading shrub with softer grey-green foliage and dark red flowers in shorter, one-sided clusters.

Grevillea honours Charles Francis Greville, a British plant collector, while banksii honours botanist Sir Joseph Banks.

Propagation. Take semi-ripe cuttings from healthy, non-flowering shoots in late summer and root them in a freely draining medium with gentle bottom heat. Seed is another option, but seedlings can vary and may hybridize where other grevilleas grow nearby.

Accepted botanical name

Grevillea banksii

In the US and Canada

Introduced in Hawaii.

Native range

Queensland.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.