Black and English walnut

Botanical names

Juglans nigra (black walnut); Juglans regia (English or Persian walnut)

Type

Large deciduous nut trees

Size

Black walnut usually around 80 feet, up to about 125 (USDA Forest Service)

Hardiness

Black walnut zones 4 to 9; English walnut zones 4 to 8, less cold hardy (Utah State University)

Where it is found

Older lots on the valley floors, about 4,000 to 5,100 feet

Known weak points

Branch dieback, nut and leaf litter, juglone, heavy limbs, shade intolerance

Walnuts are some of the oldest trees on farm lots and in old neighborhoods. Utah State University says black walnuts in northern Utah have recently shown branch dieback or been killed by borers or an unknown disease. This page covers identification, where they grow by elevation and when pruning or removal is right.

How do you identify black and English walnut?

Both have large, alternate, compound leaves. Black walnut has 15 to 23 leaflets, according to Utah State, and a strong smell when crushed; English walnut has 5 to 9 smooth-edged leaflets. The nut of black walnut is in a thick green husk; English walnut has a thinner, smoother shell. Bark is dark and deeply ridged on black walnut and smoother and pale on English walnut.

In winter you can still tell them by the stout twigs and chambered pith. Both trees have a broad, rounded crown.

• Compound leaves: 15 to 23 leaflets on black walnut, 5 to 9 on English walnut
• Round nuts in green husks
• Dark deeply furrowed bark on black walnut
• Broad rounded crown

Where does it grow in Reno, Carson City and the Carson Valley?

Both are valley-floor trees. Utah State University rates black walnut for zones 4 to 9 and notes it prefers rich, deep, well-drained bottom-land soil, and says it tolerates high pH. English walnut is rated for zones 4 to 8 and is not quite as cold hardy, so it fits warmer, protected spots such as Reno (zone 7b), Carson City (zone 7a) and Dayton (zone 7a), more than Minden (6b) or Incline Village (6b).

Both are shade intolerant, and both need space. Reno is at about 4,505 feet and Carson City at about 4,680 feet; the Tahoe towns are 1,700 to 2,600 feet higher and in zone 6b to 7a.

What goes wrong with it here?

Utah State describes black walnut branch dieback and tree death from borers or an unknown disease in northern Utah, and says leaves look worse when trees are diseased or drought stressed. See drought stress and dieback. The wood of walnut is heavy and strong, and the limbs are heavy, so a big failure matters.

The Forest Service explains that black walnut leaves, bark, husks and roots contain juglone, which inhibits many plants in the root zone. That is why gardens near a walnut often struggle. Nuts and leaves are a mess, and walnut is rated not good under power lines.

Nuts are heavy and the husks stain, so a walnut over a driveway or car is a nuisance every fall. Size is the larger issue. A mature walnut is commonly 80 feet tall with a broad crown, which puts big limbs over roofs and lines. From the ground, watch for dead branches in the top, limbs hanging low, cracks at forks and mushrooms at the base, and report them when you call.

Pruning, cabling or removal: which is the right call?

Deadwood and hanging limbs can come out any time. Large cuts are best in the dormant season. Walnuts do not take well to topping, and a crown that is cut back hard often dies back; see why topping is not pruning.

Cabling and bracing can hold a strong tree with one weak union. Removal is the answer when the trunk is hollow, much of the crown has died or a large limb is split over a structure. Most big walnuts are large tree removal jobs.

What does Battle Born Tree Service do about a walnut?

Call 775.232.8243 or use the estimate form on this page. An ISA Certified Arborist looks at the tree on site, explains what is wrong and tells you whether the job is pruning, cabling or removal. Credential WE-11728A is held by one of our two certified arborists. We do not harvest nuts or plant trees.