Northern Silky Oak Plant Care

Northern Silky Oak (Cardwellia sublimis) belongs to the Proteaceae family within the Cardwellia genus. Northern Silky Oak is native to the rainforests of northeastern Queensland, Australia.

Northern Silky Oak displays a tall, upright tree growth habit, reaching up to 30 ft tall with a spread of approximately 15 ft. Northern Silky Oak produces showy clusters of small, fragrant white flowers.

Leaf size: approximately 6 inches.

Water a young or newly planted Northern Silky Oak every 7–14 days, soaking the whole root zone, until it is established — usually one to two growing seasons. Established trees mainly need water during long dry spells. In a container, water whenever the top few centimetres of soil are dry.

Northern Silky Oak thrives in full sun to partial shade.

Cardwellia sublimis tolerates temperatures of 50–80°F. Northern Silky Oak prefers humidity levels of 50–70%. A pebble tray or humidifier helps maintain adequate moisture around the plant.

Well-draining acidic soil mix with added organic matter like peat moss and pine bark. Good drainage is essential for Northern Silky Oak to prevent waterlogging, which leads to root rot and fungal issues.

Feed Northern Silky Oak every 6 months during the growing season with a balanced, slow-release fertilizer at the rate on the label. Established trees in good soil often need little extra feeding, so let weak growth or pale foliage guide you.

Stop feeding by late summer so new growth can harden before winter.

The PlantoScan app can remind you when to water and when to fertilize each plant.

Choose a spot with full sun to partial shade and well-draining acidic soil mix with added organic matter like peat moss and pine bark. Avoid low spots where water collects after rain.

Northern Silky Oak is suited to USDA Zone 12a.

Plant container-grown or balled-and-burlapped trees in spring or early autumn, setting the root flare at soil level, and water well after planting.

Northern Silky Oak can spread to about 15 ft (4.6 m) and reach about 30 ft (9 m) tall. Space plants about 15 ft (4.6 m) apart so mature crowns don't crowd each other, and plant at least half that distance from buildings, fences and paths.

Planning a row or hedge? Try the tree spacing calculator.

Prune Northern Silky Oak while it is dormant in late winter: first remove dead, damaged and crossing branches, then thin lightly for shape.

If it flowers in spring, prune right after flowering instead so you don't remove next year's buds. Never take off more than about a quarter of the tree in one year.

Northern Silky Oak is frost-tender (hardy to USDA zone 12). In colder areas grow it in a container and move it to a bright, frost-free place before the first frost.

Northern Silky Oak can be propagated through seeds, cuttings.

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Northern Silky Oak is susceptible to aphids, scale insects, caterpillars. Inspect the foliage regularly, especially along leaf undersides and stems. Treat infestations promptly with insecticidal soap or neem oil to prevent spread.

Yellow leaves, brown tips or drooping? See common plant problems and how to fix them.

Northern Silky Oak grows outdoors in USDA Zone 12a. It survives winters down to planting zone 12a. Northern Silky Oak is native to the rainforests of northeastern Queensland, Australia. In cooler regions, grow Northern Silky Oak as a houseplant or bring it indoors before the first frost.