Japanese blue oak Plant Care

Japanese blue oak (Cyclobalanopsis glauca) belongs to the Fagaceae family within the Cyclobalanopsis genus. Japanese blue oak is native to eastern and southern Asia. Japanese blue oak is also known as Chinese evergreen oak.

Japanese blue oak displays a tall, spreading tree growth habit, reaching up to 50 ft tall with a spread of approximately 30 ft. Japanese blue oak produces small inconspicuous flowers in catkins.

Leaf size: approximately 6 inches.

Water a young or newly planted Japanese blue 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.

Japanese blue oak thrives in full sun to partial shade.

Cyclobalanopsis glauca tolerates temperatures of 50–80°F. Japanese blue oak prefers humidity levels of 40–70%.

Well-draining loamy soil with added organic matter like compost or leaf mold. Good drainage is essential for Japanese blue oak to prevent waterlogging, which leads to root rot and fungal issues.

Feed Japanese blue oak every 8 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 loamy soil with added organic matter like compost or leaf mold. Avoid low spots where water collects after rain.

Japanese blue oak is suited to USDA Zone 7b – 10b.

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.

Japanese blue oak can spread to about 30 ft (9.1 m) and reach about 50 ft (15 m) tall. Space plants about 30 ft (9.1 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 Japanese blue 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.

Japanese blue oak is hardy down to USDA zone 7b, so once established it can stay outdoors through winter in that zone and warmer ones.

Water deeply in late autumn before the ground freezes, and spread a 5–8 cm (2–3 in) layer of mulch over the root zone, keeping it away from the trunk.

Young and container-grown trees need extra protection: roots in a pot freeze much more easily than roots in the ground.

Japanese blue oak can be propagated through seeds, hardwood cuttings.

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Japanese blue oak is susceptible to oak gall wasps, oak leafhoppers. 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.

Japanese blue oak grows outdoors in USDA Zone 7b – 10b. It survives winters down to planting zone 7b. Japanese blue oak is native to eastern and southern Asia.