Black walnut Juglans nigra

Black walnut (Juglans nigra) is a deciduous perennial tree in the Juglandaceae family. It grows 15–30 m (49–98 ft) tall and 12–20 m (39–66 ft) wide, wants full sun and moderate water, and is hardy to about -30 °C (-22 °F). Space plants about 12 m (39 ft) apart.

Plan Black walnut in your garden →
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Black walnut at a glance

Is Black walnut toxic?

• People: not known to be toxic
• Cats: not well documented
• Dogs: moderately toxic
• Parts: moldy hulls, moldy nuts

Moldy hulls and nuts carry tremorgenic mycotoxins that can cause seizures in dogs.

If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.

Companion planting: what to grow with Black walnut

No well-documented helpful pairing. Group it with plants that like full sun and moderate water.

Keep apart or take care

• avoid With Tomato: Black walnut releases juglone from roots, leaves and hulls, which is documented to injure or kill this sensitive species. Evidence B
• avoid With Pear: Black walnut roots, leaves and hulls release juglone, and extension lists name this fruit as sensitive: it can wilt, stunt or die within the root zone and drip line. Evidence B
• avoid With Nashi pear (Asian pear): Pear (Pyrus) is on extension juglone-sensitive lists; Asian pear is expected to react the same way, though it is not named separately. Evidence C
• avoid With Siberian crab apple: Apple (Malus) is on extension juglone-sensitive lists; crab apples are in the same genus and are expected to be affected, though not named separately. Evidence C
• avoid With Muscadine grape: Grape (Vitis) is on extension juglone-sensitive lists; the muscadine is in a related group and is expected to be affected, though evidence is limited. Evidence C

Allelopathy: Roots, leaves and hulls release juglone, which harms many sensitive plants. (within about 15 m (49 ft))

Questions about Black walnut

How far apart should I plant Black walnut?

About 12 m (39 ft) apart, centre to centre. A mature plant spreads 12–20 m (39–66 ft).

Does Black walnut need full sun?

Full sun: at least 6 hours of direct sun a day.

How much water does Black walnut need?

Moderate water. Drought tolerance is low and waterlogging tolerance none.

How cold-hardy is Black walnut?

It tolerates about -30 °C (-22 °F) once established, roughly USDA zone 4.

Is Black walnut poisonous to cats and dogs?

For cats it is not well documented; for dogs moderately toxic; for people not known to be toxic. Moldy hulls and nuts carry tremorgenic mycotoxins that can cause seizures in dogs.

What grows well with Black walnut?

There is no well-documented companion pairing for Black walnut. Group it with plants that like the same sun (full sun) and water (moderate).

Sources and evidence

Evidence grade C (C: plausible, mixed evidence).

• ASPCA Toxic and Non-Toxic Plant List, ASPCA
• RHS Plant Finder, Royal Horticultural Society
• University extension gardening guides (general), Various land-grant university extensions
• Black walnut toxicity / juglone, University extension services

Notes and assumptions

• Typical garden-cultivar values; varieties differ.
• Juglone zone often extends to or beyond the drip line.

Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.

Related plants

• English walnut Juglans regia
• Pecan Carya illinoinensis
• Dwarf mountain pine Pinus mugo
• Japanese maple Acer palmatum
• English yew Taxus baccata
• Serviceberry Amelanchier canadensis
• Japanese flowering cherry Prunus serrulata
• Saucer magnolia Magnolia x soulangeana