Blackboard tree Plant Care

Blackboard tree (Alstonia spectabilis) belongs to the Apocynaceae family within the Alstonia genus. Blackboard tree is native to eastern Malesia, Melanesia and northern Australia. Blackboard tree is also known as Milky mangrove.

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

Leaf size: approximately 6 inches.

Water a young or newly planted Blackboard tree 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.

Blackboard tree thrives in full sun to partial shade.

Alstonia spectabilis tolerates temperatures of 60–85°F. Blackboard tree prefers humidity levels of 50–80%. A pebble tray or humidifier helps maintain adequate moisture around the plant.

Well-draining loamy soil with added organic matter for moisture retention. Good drainage is essential for Blackboard tree to prevent waterlogging, which leads to root rot and fungal issues.

Feed Blackboard tree 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 loamy soil with added organic matter for moisture retention. Avoid low spots where water collects after rain.

Blackboard tree is suited to USDA Zone 10b – 12b.

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.

Blackboard tree 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 Blackboard tree 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.

Blackboard tree is frost-tender (hardy to USDA zone 10). In colder areas grow it in a container and move it to a bright, frost-free place before the first frost.

Blackboard tree can be propagated through seeds, stem cuttings. Similar propagation techniques also apply to stinkwood plant care, which shares the same genus.

See all plants toxic to cats and plants toxic to dogs.

Blackboard tree is susceptible to aphids, scale insects, mealybugs. 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.

Blackboard tree grows outdoors in USDA Zone 10b – 12b. It survives winters down to planting zone 10b. Blackboard tree is native to eastern Malesia, Melanesia and northern Australia. In cooler regions, grow Blackboard tree as a houseplant or bring it indoors before the first frost.