Black Walnut (Juglans nigra)

How much light does a Black Walnut need?

Full sun suits black walnut best of all. Give it a spot with at least six hours of direct light each day. It also tolerates part shade, so a site with a little shade in the afternoon still lets it grow well. Full sun tends to produce a fuller, more even canopy than a shadier spot. Pick the sunniest open spot you have, since full sun gives the strongest growth. Once established, it holds its shape in either light level listed here.

• Light: Full sun and part shade (full sun preferred)¹

How often to water a Black Walnut

Check the soil before you water, aiming for conditions that stay moist to consistently wet rather than dry. This tree prefers organically rich, well-drained ground that holds moisture without staying soggy. In the ground outdoors, it also tolerates soil that is occasionally wet or occasionally dry. Overall, this tree's water need ranges from medium moisture up to fairly wet conditions. It also tolerates soil that swings to occasionally dry or to occasionally wet.

• Water: Medium to wet¹

Best soil for a Black Walnut

Organically rich ground that drains well but still holds some moisture suits black walnut best. This tree also tolerates soil that runs occasionally dry or occasionally wet. Keep that ground evenly moist to wet, matching the water needs listed for this tree. Soil pH can run from a fairly acidic 5.0 up to an alkaline 8.0 for this species. That span covers acid soil at one end and alkaline soil at the other.

• Soil drainage: Well drained, moist, occasionally dry and occasionally wet¹
• Soil pH: pH 5–8²

Hardiness and temperature

USDA zones 4a through 9b mark the hardiness range for this tree. That range runs from cold northern winters to mild, almost subtropical conditions in the warmest zone. Most of the tree's native range across the eastern and central United States falls inside this span. Your zone number is the most reliable guide to whether winters in your area suit this tree.

• Hardiness: Zones 4a–9b¹

Fertilizing a Black Walnut

Feed black walnut once a year with a light application of nitrogen rather than a heavy regular schedule. Time that feeding for early spring, around March or April, just as the tree starts active growth for the season. Outside of that single light feeding, this species does not need extra fertilizer through the rest of the year.

• Fertilizer: Light, once a year (Mar–Apr)³

How to plant a Black Walnut

Choose a site within USDA zones 4a through 9b before you plant. This wide range spans cold northern winters and warm southern summers alike. Pick a permanent spot, since this tree grows tall and wide and resists being moved once established. Gardeners at the warm edge, zone 9b, should expect hotter summers than this tree sees further north. Gardeners at the cold edge, zone 4a, should pick the most sheltered spot the yard offers. If your winters run colder than zone 4a, this tree is not a safe long-term choice for your yard. Check your local zone before you dig, since this tree is difficult to relocate later.

• Hardiness: Zones 4a–9b¹

Winter care

Within USDA zones 4a through 9b, this tree survives typical winter lows. This page has no cited minimum temperature for black walnut. Use your zone number as the guide, since it reflects typical winter lows for your area. Zone 4a marks the coldest winters this tree is known to handle. Mulch young trees over winter if you garden near that cold edge. Past zone 9b, summer heat rather than winter cold becomes the bigger concern. Outside the 4a-9b range, this tree is not a dependable choice for winter survival.

• Hardiness: Zones 4a–9b¹

How to propagate a Black Walnut

Seed is the way to grow new black walnut trees. This is the only method confirmed for the species on this page, so skip cuttings or division if you want a true result. Collect sound, undamaged nuts from the ground after they drop to start new trees. Growing from seed is the method documented for this tree.

• Propagation: Seed⁴

Common problems

Several pests target this tree, including aphids, fall webworm, foliage-chewing caterpillars, walnut husk fly, and walnut twig beetle. Diseases to watch for include anthracnose, bacterial blight, root rot, canker, leaf spot, shoot dieback, and thousand cankers disease. Thousand cankers disease is spread by the walnut twig beetle and can kill a tree, so report dieback or branch death to your local extension office.

• Common pests: aphids, fall webworm, foliage chewing caterpillars, walnut husk fly and walnut twig beetle^1,5
• Common diseases: anthracnose, bacterial blight, root rot, canker, leaf spot, shoot dieback and thousand cankers disease¹

Questions and answers

Is black walnut toxic to dogs?

Yes, the ASPCA lists black walnut as toxic to dogs. If your dog chews on this tree and shows symptoms, contact your vet or a pet poison line right away. This rating comes from the ASPCA's own records for this species.

Is black walnut safe for cats?

The ASPCA and NC State Extension's plant database both list black walnut as non-toxic to cats. Dogs get a different rating from the same sources, which list black walnut as toxic for them.

How fast does black walnut grow?

Black walnut has a rapid growth rate. It is a deciduous tree that can reach 50-90 ft (15.2-27.4 m) tall at maturity, with a spread of 50-75 ft (15.2-22.9 m).