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Black Walnut
A magnificent native nut-and-timber tree bearing rich, boldly flavored black walnuts - but famous for the juglone in its roots that stunts or kills many nearby plants, so it must be sited with care, well away from the garden.
Safety notes The kernel is safe food and a common tree-nut allergen. The tree's main hazard is to OTHER PLANTS: roots, leaves, and hulls release juglone, which stunts or kills tomatoes, peppers, apples, blueberries and azaleas. Green hulls stain badly - wear gloves. Fallen nuts and hulls left on damp ground grow moulds toxic to DOGS (tremors, seizures): pick up drops promptly and keep the hull pile out of a dog's reach. Never bed horses on walnut shavings or sawdust - it causes laminitis.
Overview
Black walnut (Juglans nigra) is one of the most valuable and distinctive native trees of eastern North America - a tall (50-75+ foot), long-lived hardwood that yields both a prized nut and some of the most valuable timber on the continent. Its nuts have a rich, bold, unmistakable flavor far stronger than the mild English (Persian) walnut sold in stores, treasured in baking, ice cream, and confections. It's a handsome, high-crowned shade tree with dark, deeply furrowed bark and airy compound leaves.
Quick facts
- Sprouts in
- 60 daysRange: 30–120 days
- Soil temperature
- 65 °FRange: 55–75 °F
- Height
- 70 ftRange: 50–100 ft
- Spread
- 65 ftRange: 50–80 ft
- Cold
- Takes hard frostdamaged below -30°F
- Heat
- Struggles above 100°F
- Life cycle
- Perennial, lives about 150 years
- Save seeds
- About 180 days after plantingRange: 150–210 days
- Self-sows
- Yes, expect volunteers
- Soil
- Well-drained
- Water
- Medium
- Plant spacing
- 60 ftRange: 40–80 ft
When to plant
Fall sowing is open for 19 more days. Next: spring, Mar 27 to May 22.
- Direct sow Sep 27 – Nov 8 Open now · 19 days leftAbout 4 weeks before to 2 weeks after your first frost (Oct 25 here)Plant whole nuts (in the hull is fine) in fall right where the tree will grow; they need winter stratification and germinate in spring, forming a strong taproot. Protect from squirrels with a screen. Direct-sown trees establish well.
- Transplant Mar 27 – May 22 Opens in 158 daysAbout 2 weeks before to 6 weeks after your last frost (Apr 10 here)Plant a young container or bare-root black walnut in early spring into deep, rich, well-drained soil in full sun; plant small, since the taproot resents disturbance. Site it FAR from vegetable gardens and juglone-sensitive plants.
Frost here: last around Apr 10 (Mar 27 to Apr 24 most years), first around Oct 25. Zone averages, your own yard may run a week or two either way.
Life stages
Establish, grow, repeat
Getting established and returning each season are different parts of the story.
Stage 1 of 5 · Getting established
Years 1-3 - young tree
About the first 3 years after planting
Care at this stage
-
Water while establishing
Water a young black walnut deeply and regularly through its first 2-3 years. It grows a deep taproot and resents transplanting, so plant it small (or from a nut in place). Give it deep, rich, well-drained soil for best growth - it's a bottomland tree at heart.
-
Site it FAR from the vegetable garden and sensitive plants
The critical siting rule: black walnut roots release JUGLONE, which stunts or kills tomatoes, peppers, potatoes, apples, blueberries, azaleas, and many other plants within (and beyond) its root zone. Plant it well away from vegetable gardens, orchards, and sensitive ornamentals - and remember the toxic zone expands as the tree grows.
-
Mulch the root zone (keep hulls out of compost)
A wide mulch ring helps the young tree, but don't mulch sensitive plants with black walnut leaves, hulls, or wood chips, which carry juglone. Keep walnut debris out of the vegetable garden and general compost.
Months are typical seasonal windows; climate, variety, and plant age can shift them.
Harvest
- Green hulls softened and turned yellowish, nuts dropping in fall
- The hull dents under thumb pressure (ripe); firm green hulls are not ready
- Kernel inside a test nut is plump and tan, not shriveled
- Nuts gathered promptly and hulled before the hull rots black on the kernel
- Gather nuts as they drop, and hull promptly (with gloves!) · every 3 days
- Race the squirrels
- Keep dogs away from the drops and the hull pile
Per plant 200 to 6000 nuts, 6 to 120 lbPicking pick as they ripen
Cook with Black Walnut
Watch out for
3 to know. 2 are high-risk: Juglone Toxicity (Allelopathy), Thousand Cankers Disease. 1 is active in October.
Juglone Toxicity (Allelopathy)Severity High DisorderSeason: Apr–SepSensitive plants near a black walnut yellowing, wilting, stunting, and dying (often suddenly in summer) while unaffected species nearby look fine; the damaged zone expanding as the tree grows.
Sensitive plants near a black walnut yellowing, wilting, stunting, and dying (often suddenly in summer) while unaffected species nearby look fine; the damaged zone expanding as the tree grows.
Move sensitive plants out of the root zone (raised beds with a barrier help but aren't foolproof near roots); replace with juglone-tolerant species. There's no way to neutralize juglone in the soil around a living tree.
Site black walnut well away from vegetable gardens, orchards, and sensitive ornamentals; grow only juglone-tolerant plants in its root zone; keep walnut leaves, hulls, and wood chips out of gardens and compost. The toxic zone can persist for years after a tree is removed.
Black walnut's defining trait: its roots (and, to a lesser degree, leaves and hulls) release juglone, a natural allelopathic compound that stunts, wilts, and kills many sensitive plants - tomatoes, peppers, potatoes, eggplant, apples, blueberries, azaleas, rhododendrons, peonies, and more - within and beyond the tree's root zone. This is a hazard to your other plants, not to people.
Thousand Cankers DiseaseSeverity High DiseaseSeason: May–SepYellowing, thinning, and dieback of the upper crown, numerous small dark cankers under the bark around tiny beetle entry holes, and progressive decline over a few years.
Yellowing, thinning, and dieback of the upper crown, numerous small dark cankers under the bark around tiny beetle entry holes, and progressive decline over a few years.
There is no cure - infected trees usually decline and die. Remove and properly dispose of affected wood on site (don't transport it), and consult a forester or extension office, especially in or near known outbreak areas.
Keep trees vigorous and unstressed; crucially, DO NOT move walnut firewood or wood between regions, which spreads the beetle and fungus; buy local nursery stock and follow any regional quarantines.
A serious, sometimes fatal disease of walnuts caused by a fungus (Geosmithia) carried by the tiny walnut twig beetle. The beetles create countless small cankers beneath the bark that coalesce and girdle branches and trunks, causing progressive dieback and death, especially of black walnut. It has spread through parts of the West and pockets of the East.
Walnut Husk FlySeverity Low PestnowSeason: Aug–OctBlack, soft, slimy husks in late summer that cling to the shell, small white maggots inside the rotting husk, and stained, hard-to-hull nuts.
Black, soft, slimy husks in late summer that cling to the shell, small white maggots inside the rotting husk, and stained, hard-to-hull nuts.
Rarely warrants spraying on a home tree - sanitation (removing dropped, infested hulls) is the main control, and the kernel inside stays sound. Just hull affected nuts promptly and clean the stained shells.
Gather and destroy dropped, infested nuts promptly to break the cycle; hang yellow sticky traps to monitor emergence; hull nuts immediately after gathering so the maggots can't taint the kernel.
The signature late-season walnut pest: a fly that lays eggs in the husk, and whose maggots tunnel through it, causing the husk to blacken, soften, and rot, and to stick tightly to the shell so it won't hull cleanly - staining the shell and darkening the kernel if left on, though the maggots rarely reach the nut itself.
Good & bad neighbors
First rule: keep Tomato apart. The classic juglone victim: tomatoes (and peppers, potatoes, eggplant) planted within a black walnut's root zone wilt, yellow, and die.
Plant nearby
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Many native prairie wildflowers, including black-eyed Susan, tolerate juglone and thrive in a black walnut's root zone where garden plants can't - a good choice for a walnut understory planting.
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Pawpaw is notably juglone-tolerant and a native understory fruit tree - one of the better edibles to grow near or under a black walnut, where most fruit trees would fail.
Keep apart
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The classic juglone victim: tomatoes (and peppers, potatoes, eggplant) planted within a black walnut's root zone wilt, yellow, and die. Keep the vegetable garden well away from the tree.
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Apples and many other fruit trees are juglone-sensitive and decline near black walnut; don't plant an orchard within (or downhill of) a walnut's expanding root zone.
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Blueberries are juglone-sensitive and do poorly near black walnut, on top of their need for acidic soil - keep them well away from the tree's roots.
Varieties · 3
You pick one when you add Black Walnut to your garden. Its days to maturity set your harvest window.
Black Walnut (Juglans nigra) - wild seedling
The wild native: a tall (50-75+ foot) nut-and-timber tree with rich, boldly flavored nuts in very hard shells, and roots that release juglone.
Variety details for Black Walnut (Juglans nigra) - wild seedling
Tall, high-crowned tree with dark furrowed bark, airy compound leaves, and round green-hulled nuts.
speciesnativejuglonehard-shellNut size and crackability vary tree to tree. Superb flavor and timber, but must be sited well away from gardens and sensitive plants.
Thomas
A classic, widely grown black walnut cultivar selected for large nuts, relatively easy cracking, and reliable, early, heavy production - a longtime favorite for home growers wanting better, more crackable nuts than a random seedling.
Variety details for Thomas
Productive tree bearing large nuts with a relatively good kernel and crack.
cultivarlarge-nuteasier-crackingproductiveEmma K
A cold-hardy, productive cultivar prized for high-quality, well-filled kernels and good cracking, well suited to northern black-walnut growing - a strong choice where flavor, kernel quality, and hardiness matter.
Variety details for Emma K
Hardy, productive tree with well-filled, good-quality kernels.
cultivarcold-hardyhigh-quality-kernelproductive
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