Black Walnut Plant Care

Black Walnut (Juglans nigra) belongs to the Juglandaceae family within the Juglans genus. Black Walnut is native to central and eastern North America, growing mostly in riparian zones. Black Walnut is also known as Eastern Black Walnut, American Black Walnut.

Black Walnut displays a tall, deciduous tree growth habit, reaching up to 100 ft tall with a spread of approximately 50 ft. Black Walnut produces inconspicuous greenish flowers.

Leaf size: approximately 12 inches.

Water a young or newly planted Black Walnut 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.

Black Walnut thrives in full sun.

Juglans nigra tolerates temperatures of 0–100°F. Black Walnut prefers humidity levels of 30–70%.

Rich, well-draining soil with good organic content. Good drainage is essential for Black Walnut to prevent waterlogging, which leads to root rot and fungal issues.

Feed Black Walnut 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 and rich, well-draining soil with good organic content. Avoid low spots where water collects after rain.

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.

Black Walnut can spread to about 50 ft (15.2 m) and reach about 100 ft (30 m) tall. Space plants about 50 ft (15.2 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 Black Walnut 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.

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.

Black Walnut can be propagated through seeds, grafting.

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Black Walnut is susceptible to walnut caterpillars, walnut husk flies. 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.