Tree · Juglandaceae
Walnut
Juglans regia
Give it deep soil, full sun, and room to spread, and a walnut shades the yard for generations while it fills baskets each fall.
Full sun
Every 7–21 days
USDA 5–9
39–59 ft · 12–18 m
Overview
A walnut is a long-lived shade tree grown as much for its nuts as for its presence in the landscape. It belongs to the walnut family and reaches up to 60 feet (18 m) tall with a wide, open crown, so it needs real space to itself. Give it deep, fertile soil and full sun and it can crop and shade a yard for generations.
The English or Persian walnut sold for its kernels is the tree most growers plant, while the native black walnut is its tougher cousin, prized for hard-shelled nuts and dark timber. Both make a strong compound called juglone that seeps from their roots and hulls and holds back sensitive plants nearby. That trait shapes where you put the tree and what you grow under it.
Walnuts ask for patience more than fuss. A grafted tree takes several years to bear, and the falling nuts with their staining hulls make a mess on paving below. Plant it well clear of the house and walks, and the payoff is shade, structure, and a steady fall harvest.
Care
The short version: full sun and deep, well-drained loam, with steady deep watering while the tree is young and only periodic irrigation once it is established. Feed in early spring, prune in late summer to avoid heavy sap bleed, and give it plenty of room.
Light
Walnuts need full sun to crop well, taking only light partial shade. A tree crowded by buildings or larger trees grows lopsided and bears far fewer nuts, so give it open sky on all sides.
Water
Water young trees deeply every 1 to 3 weeks through their first few seasons to settle the roots. An established walnut is fairly drought tolerant, but it still sets the heaviest crop when you give it a deep soak now and then through a dry summer.
Soil
Plant in deep, fertile, well-drained loam. A pH of 6.0 to 7.5 suits it, and the one thing it won't forgive is wet feet, so steer clear of waterlogged or shallow ground where the roots can't run.
Temperature
A walnut is hardy and handles a wide range, from about -22°F to 95°F (-30°C to 35°C). The catch is timing, since a late spring frost can nip the young growth and catkins, which is why later-leafing cultivars carry an edge in cold areas.
Humidity
Average outdoor humidity of 40% to 70% sits fine with a walnut. Damp, still air during a wet spring feeds blight, so an open canopy that dries fast matters more than the number on a gauge.
Feeding
Feed in early spring before the growth flush, using a nitrogen-focused balanced fertilizer guided by a soil or leaf test. Walnuts are heavy feeders for nitrogen, but test first rather than guess, since too much is wasted and washes away.
Pruning
Train a young tree to a single central leader, then thin out dead, crossing, and low limbs as it grows. Time the work for late summer or early fall, because a walnut bleeds sap badly from cuts made in late winter and spring.
Repotting
A walnut is a landscape and orchard tree, not a container plant, so there is no repotting once it's in the ground. If you hold a young tree in a nursery pot too long, watch for roots circling the pot and stalled top growth, and get it planted out.
Size & spacing
Plan for a big tree, 40 to 60 feet (12 to 18 m) tall with a spread of 33 to 49 feet (10 to 15 m). Set it well clear of buildings, walks, and other trees so the crown has room and the staining nuts don't fall on paving.
When to plant
Walnuts run on the seasons and want planting while they are dormant. Set bare-root or balled trees out in late winter to early spring, watch for the wind-pollinated catkins in spring, and gather the ripe nuts in fall once the hulls split.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Plant bare-root or balled-and-burlapped trees during dormancy, late winter to early spring
- Harvest: Wind-pollinated catkins in spring (April to May); nuts ripen and are harvested in fall, September to October
Hardiness
USDA hardiness zones: 5–9
Temperature: down to -29°C
Troubleshooting
Most walnut trouble shows up on the nuts in summer or on the leaves toward fall. Catch the early signs of a pest or blight and you can protect that year's crop before it drops. Match what you see below, then act while it still counts.
Black, slimy husks with maggots inside
This is the walnut husk fly, whose maggots feed in the husk and stain the shell as the tissue rots. Hang yellow sticky traps by June and spray a bait insecticide at the first steady catch. Rake up and destroy the fallen, infested nuts so the flies can't carry over to next year.
Fix:
- Monitor with supercharged sticky traps from early summer
- Apply a bait insecticide spray at first sustained fly catch
- Pick up and destroy fallen, infested nuts
Frass-filled entry holes and nuts dropping early
Codling moth larvae bore straight into the nuts, leaving frass at the entry hole and ruining the kernel. Set pheromone traps in mid-March, track degree-days to time your sprays after biofix, and consider mating disruption across the orchard. Clearing the infested drops and mummies keeps the next generation from building up.
Fix:
- Use pheromone mating disruption in the orchard
- Time insecticide sprays by degree-day models after biofix
- Remove infested drops and mummies
Greasy black spots on young nuts and shoots in wet weather
Walnut blight, a bacterium that spreads in wet, mild spring weather, blackens young nuts and tissue and can drop a heavy share of the crop. Time copper-based bactericide sprays with a leaf-wetness model and keep the canopy open so it dries fast. Choosing a later-leafing cultivar sidesteps the worst of the wet window.
Fix:
- Apply copper-based bactericide sprays timed by a wet-weather model
- Improve air movement and avoid overhead wetting
Yellow leaves with dark blotches dropping in late summer
Dark angular spots that turn into early leaf fall point to anthracnose and related leaf-spot fungi, made worse by a wet spring or a drought-stressed summer. Rake and destroy the fallen leaves to cut down the spores that overwinter. Deep watering through dry spells keeps the tree strong enough to shrug it off.
Fix:
- Rake and destroy fallen leaves to reduce inoculum
- Water deeply during dry spells to limit stress
Toxicity
The shelled nuts are good to eat and safe for people, but the rest of the tree calls for care. The wood and shavings carry juglone and cause laminitis in horses, while a moldy fallen nut can bring tremors and seizures in dogs. Rake up the drops, bin anything moldy, and never bed a horse on walnut shavings.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Caution
A shelled kernel won't poison a cat, but the high fat can bring on vomiting and a loose stomach. Keep fallen and moldy nuts out of reach, since mold on a walnut carries the same toxins that set off tremors.
Dogs Caution
Plain kernels aren't systemically toxic, yet whole nuts can choke a dog or lodge in the gut, and the fat alone often triggers vomiting. The real danger is a moldy walnut off the ground, which can bring on muscle tremors and seizures within hours.
Horses Severe
Black walnut shavings used as bedding cause laminitis. Watch for a reluctance to move, swollen lower limbs, heat in the hooves, and a pounding digital pulse, sometimes within a day of contact. Never let walnut wood or sawdust near a stable.
Rabbits Caution
Walnuts have no place in a rabbit's diet. The rich, fatty kernel can throw off a gut built for grass and hay, so keep the nuts and hulls away from any hutch.
Livestock Caution
Grazing animals do best kept off fallen walnuts and hulls. The fatty nuts can sour the rumen, and a pile of moldy drops carries the same mycotoxins that harm dogs.
Birds Caution
A small piece of plain kernel suits some birds, but the high fat adds up fast and a moldy nut is dangerous. Offer only fresh, unspoiled bits and clear away anything that has fallen and started to rot.
People Shelled nuts safe
Shelled walnuts are a wholesome food and safe to eat. Toss any nut that smells musty or shows mold, and keep the staining hulls and walnut sawdust off your skin.
Keep fallen nuts and hulls raked up, discard any moldy nuts, and never use walnut shavings or sawdust as horse bedding.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
United Kingdom
Animal PoisonLine: 01202 509000 (fee applies)
Australia
Animal Poisons Helpline: 1300 869 738
Varieties
A handful of walnut cultivars cover most home and orchard plantings. These are the ones worth knowing by name.
'Chandler'
A leading lateral-bearing English walnut prized for its high yields of light, clean kernels, and its late leafing dodges the worst of the spring frost.
'Franquette'
A late-leafing French cultivar that bears on its terminals and earns its keep as a pollinizer on cooler, frost-prone sites.
Black walnut (Juglans nigra)
The native North American species with darker, hard-shelled nuts and prized timber, and it is the main source of juglone, toxic to horses, and the usual rootstock under English walnut.
'Carpathian'
A cold-hardy strain of English walnut tough enough to come through winters down to roughly USDA zone 5.
Companions
Walnuts make life hard for juglone-sensitive plants in their root zone, so the best neighbors are the few species that shrug off juglone and grow happily beneath the canopy.
Keep apart
tomato: Solanaceous crop highly sensitive to juglone; wilts and dies within the walnut root zone.
potato: Juglone-sensitive; stunts and yellows near walnut roots and hulls.
apple: Apple trees decline and can die from juglone exposure near walnuts.
blueberry: Highly juglone-sensitive; foliage yellows and plants collapse near walnuts.
How to propagate
Walnuts are propagated by grafting for a known crop or grown from seed when the nut itself is the goal, though seed is slow and never true to the parent.
GraftingDemanding
Late winter to spring (bench grafting or field budding) · About 4-7 years to a meaningful nut crop
Almost every named walnut starts as a graft. Growers join an English walnut scion onto black walnut or Paradox rootstock in late winter or spring for the vigor and pest tolerance the roots provide, and the young tree takes about 4 to 7 years to give a meaningful nut crop.
SeedModerate
Sow stratified nuts in fall, or cold-stratify and sow in spring · Seedlings may take 8-12 or more years to bear and are used mainly as rootstock
Growing from seed is simple but slow and unpredictable. Cold-stratify the nuts for about 90 to 120 days, then sow in spring, or plant stratified nuts straight into fall ground. The seedlings won't match the parent cultivar and may take 8 to 12 years or more to bear, so most end up as rootstock for grafting.
Myths
A walnut tree poisons everything planted near it.
The tree releases a compound called juglone that does hit sensitive plants like tomato, potato, apple, and blueberry, but mostly within the drip line. Plenty of species are juglone-tolerant and grow just fine nearby, so the ground under a walnut is not a dead zone.
Walnuts are a safe, healthy snack for dogs.
A plain kernel won't poison a dog, but it is rich enough to cause an upset stomach, and a whole nut can choke or block the gut. A moldy walnut is the real hazard, carrying mycotoxins that bring on tremors and seizures.
Plant a walnut from seed and you'll harvest the same variety.
Named English walnuts are grafted onto black walnut or Paradox rootstock, so the seed inside a nut does not breed true. A seedling is a gamble that grows variable nuts and takes many years to bear.