Alloxylon flammeumRed Silky Oak

The Alloxylon flammeum, commonly known as the Red Silky Oak or Queensland Tree Waratah, is an upright rainforest tree in the Proteaceae, grown for the bright red to orange-red flower heads it carries at its branch ends in spring. Each head is a cluster of up to fifty tubular flowers, and because the tree often flowers when it is sparsely leaved the display is unobscured. It is a magnet for honeyeaters.

Reaching around 8 to 12 metres in cultivation, it makes a substantial feature or avenue tree. It is listed as Vulnerable under Australia's Environment Protection and Biodiversity Conservation Act, most of its upland rainforest habitat having been cleared, so growing it is a conservation-positive choice.

Specifications

• Height8 to 12 metres in cultivation, to 33 metres in wild rainforest
• Width4 to 6 metres
• Native toThe Atherton Tablelands of far north Queensland, Australia, between about 700 and 820 metres altitude
• FoliageGlossy dark green elliptic adult leaves 8 to 25 cm long with smooth entire margins. Juvenile foliage is deeply lobed and looks quite different; evergreen
• Growth rateModerate to fast

Conditions

• SoilWell-drained soils rich in organic matter but low in phosphorus. Like most Proteaceae it is phosphorus sensitive, so avoid standard high-phosphorus fertiliser
• LightFull sun to light shade
• WaterModerate; survives extended dry spells once established, though flowering is reduced under drought
• ClimateNotably adaptable for an upland tropical species, and grown successfully well south of its natural range. Established trees tolerate moderate frost

Additional Features

• FlowersTerminal heads of ten to fifty bright red to orange-red tubular flowers, clusters to about 75 mm across, from August to October
• FruitWoody follicles 7 to 10 cm long holding eight to ten winged seeds, ripening February to March
• FormSingle-trunked, upright to pyramidal tree
• UsesFeature and specimen flowering tree, avenue and park planting, rainforest revegetation, and bird-attracting habitat gardens
• SpacingPlant 5 to 8 metres apart for avenue or grouped planting
• Wildlife AttractionBird pollinated; strongly attracts honeyeaters
• Conservation StatusListed as Vulnerable under the Australian Environment Protection and Biodiversity Conservation Act 1999
• NutritionSusceptible to iron-deficiency chlorosis, which is correctable with iron chelate
• Seasonal AppealEvergreen canopy with a spectacular spring flowering display

The Red Silky Oak is a striking flowering tree for large gardens, parks and avenues, and one of the most rewarding of the Australian Proteaceae to grow at scale.

Naming note: The name "red silky oak" is also applied in the trade to Grevillea banksii, an unrelated coastal Queensland shrub with deeply divided leaves and one-sided toothbrush flower spikes. This listing is the Atherton Tableland rainforest tree, Alloxylon flammeum.