Tree · Juglandaceae
Walnut
Juglans regia
Given deep soil, full sun, and room to spread, a walnut becomes the tree that shades a garden for generations and fills baskets each fall.
Full sun
Every 7–21 days
USDA 5–9
39–59 ft · 12–18 m
Overview
A walnut earns its place as a long-lived shade tree, grown for its nuts and for the quiet grandeur it lends a property. Part of the walnut family, it rises to 60 feet (18 m) beneath a wide, open crown, so it wants a stage of its own rather than a spot in a crowded border. Set it in deep, fertile soil under full sun, and it will shade and crop across generations.
For the kitchen, most gardeners choose the English or Persian walnut, while the native black walnut offers hard-shelled nuts and the dark, coveted timber. Both, though, release a compound called juglone from their roots and hulls that unsettles a handful of sensitive plants nearby. That single trait guides where the tree belongs on the plot and which companions can share its ground.
A walnut is a tree for the patient, and for the long view of a garden. Grafted specimens take several years to bear, and the dropping nuts with their staining hulls leave their mark on any paving beneath. Give it a setting well away from the house and the walking paths, and it repays you with cooling shade and a harvest each fall.
Care
The short version: full sun and deep, well-drained loam set the stage, with deep watering while the tree is young and only periodic soaks once it is established. Feed in early spring, prune in late summer to avoid heavy sap bleed, and give it generous room.
Light
A walnut wants full sun to crop well and accepts only light partial shade. Placed in the shadow of buildings or taller trees, it leans and grows lopsided and sets far fewer nuts, so reserve an open, sunlit stretch of the garden for it.
Water
Through its first few seasons, give a young tree a deep drink every 1 to 3 weeks so it settles into its spot. An established walnut handles dry weather with ease, though a deep soak now and then across a dry summer keeps the harvest at its best.
Soil
Choose deep, fertile, well-drained loam for the planting site. A pH of 6.0 to 7.5 suits it, and the one condition it will not abide is wet feet, so avoid any low, waterlogged, or shallow corner of the garden where water lingers.
Temperature
A walnut is at home across a wide climate, from about -22°F to 95°F (-30°C to 35°C). The concern is timing rather than cold itself, since a late spring frost can catch the young growth and catkins, which is why later-leafing cultivars suit colder gardens best.
Humidity
Ordinary outdoor humidity of 40% to 70% asks nothing special of a walnut. Still, damp, quiet air in a wet spring encourages blight, so a setting with good airflow and an open canopy matters more than any figure on a gauge.
Feeding
Feed in early spring ahead of the growth flush with a nitrogen-focused balanced fertilizer, guided by a soil or leaf test. A walnut leans on nitrogen, but a test keeps the feeding measured, since any excess simply drains away unused.
Pruning
Shape a young tree to a single central leader, then thin the dead, crossing, and low limbs as the crown fills out. Time the work for late summer or early fall, because a walnut bleeds sap heavily from cuts made in late winter and spring.
Repotting
A walnut belongs in the landscape and the orchard, not in a container, so once it is planted there is no repotting to consider. A young tree left too long in a nursery pot shows roots circling the pot and stalled top growth, a sign to settle it into the ground.
Size & spacing
Plan the setting for a substantial tree, 40 to 60 feet (12 to 18 m) tall with a spread of 33 to 49 feet (10 to 15 m). Give it clearance from buildings, walks, and neighboring trees so the crown can open fully and the staining nuts stay off the paving.
When to plant
A walnut keeps to the garden's seasons and prefers planting during dormancy. Settle bare-root or balled trees into their place in late winter to early spring, mark the wind-pollinated catkins that arrive in spring, and gather the ripe nuts in fall as the hulls split open.
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
A walnut's troubles tend to gather on the nuts through summer and on the leaves as fall draws near. Read the early signs of a pest or a blight and you can protect that season's crop before it falls. Match what appears below, then act while the moment still holds.
Black, slimy husks with maggots inside
Blackened, softening husks that stain the shell are the mark of the walnut husk fly, whose maggots feed inside as the tissue rots. Set yellow sticky traps out by June to catch the timing, then apply a bait insecticide once the catch turns steady. Rake up and destroy the fallen, infested nuts so the flies do not return the following season.
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 at the entry holes and nuts falling early
Frass at a tidy entry hole and nuts loosing early are the calling card of codling moth, whose larvae bore into the kernel itself. Set pheromone traps in mid-March, follow degree-days to time the sprays after biofix, and weigh mating disruption across the orchard. Gathering the infested drops and mummies keeps the next generation from gaining ground.
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
Greasy black marks spreading over young nuts, catkins, and shoots in a mild, wet spring signal walnut blight, a bacterium that can strip away a large part of the crop. Time copper-based bactericide with a leaf-wetness model and keep the canopy open so it dries fast. A later-leafing cultivar steps neatly around the wettest 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 falling in late summer
Dark angular spots that end in early leaf fall usually mean anthracnose and its leaf-spot kin, sharpened by a wet spring or a drought-stressed summer. Rake and destroy the fallen leaves to thin the spores that overwinter. A deep watering through dry spells holds the tree's vigor and lets it carry on unbothered.
Fix:
- Rake and destroy fallen leaves to reduce inoculum
- Water deeply during dry spells to limit stress
Toxicity
The shelled nuts belong happily in the kitchen and are safe for people, yet the rest of the tree asks for a measure of care. The wood and shavings carry juglone and cause laminitis in horses, and a moldy fallen nut can bring tremors and seizures in dogs. Keep the drops raked up, discard 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 will not poison a cat, though the high fat can lead to vomiting and a loose stomach. Keep fallen and moldy nuts out of reach, since the mold on a walnut carries the very toxins that set off tremors.
Dogs Caution
Plain kernels are not systemically toxic, yet a whole nut can choke a dog or lodge in the gut, and the fat alone often prompts vomiting. The real danger is a moldy walnut lifted from the ground, which can bring on muscle tremors and seizures within hours.
Horses Severe
Walnut shavings spread as bedding cause laminitis. Look for a reluctance to move, swollen lower limbs, heat in the hooves, and a pounding digital pulse, at times within a day of contact, and keep walnut wood or sawdust away from the stable.
Rabbits Caution
Walnuts have no place in a rabbit's diet. The rich, fatty kernel unsettles a gut built for grass and hay, so keep the nuts and hulls clear of any hutch.
Livestock Caution
Grazing animals fare best kept off fallen walnuts and hulls. The fatty nuts can sour the rumen, and a heap of moldy drops carries the same mycotoxins that harm dogs.
Birds Caution
A small piece of plain kernel suits some birds, though the fat mounts quickly and a moldy nut is dangerous. Offer only fresh, unspoiled morsels and clear away anything fallen that has begun to rot.
People Shelled nuts safe
Shelled walnuts are a wholesome food and safe to eat. Discard any nut that smells musty or shows mold, and keep the staining hulls and walnut sawdust off the 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 short list of cultivars suits most gardens and orchards, each with its own place in the planting plan. These are the names worth carrying to the nursery.
'Chandler'
'Chandler' stands among the leading lateral-bearing English walnuts, admired for generous yields of light, clean kernels, and its late leafing slips past the worst of the spring frost.
'Franquette'
'Franquette', a late-leafing French cultivar, bears on its terminals and holds a valued role as a pollinizer on cooler, frost-prone sites.
Black walnut (Juglans nigra)
Black walnut, the native North American species, carries darker, hard-shelled nuts and prized timber; it is the chief source of juglone, toxic to horses, and the customary rootstock beneath English walnut.
'Carpathian'
'Carpathian' is a cold-hardy strain of English walnut, hardy enough to weather 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
A walnut arrives by grafting when a known crop is the aim, or from seed when the nut itself is the reward, though seed is slow and never faithful to the parent.
GraftingDemanding
Late winter to spring (bench grafting or field budding) · About 4-7 years to a meaningful nut crop
Nearly every named walnut comes to the garden as a graft. An English walnut scion is joined to black walnut or Paradox rootstock in late winter or spring for the vigor and pest tolerance those roots lend, and the young tree takes about 4 to 7 years to reach 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
Raising a walnut from seed is simple yet slow and unpredictable. Cold-stratify the nuts for about 90 to 120 days and sow in spring, or set stratified nuts straight into fall ground. The seedlings do not echo the parent cultivar and may take 8 to 12 years or more to bear, so most serve as rootstock for grafting.
Myths
A walnut tree poisons everything planted near it.
The tree does release juglone, which troubles sensitive plants like tomato, potato, apple, and blueberry, but chiefly within the drip line. Many species tolerate juglone and settle in happily nearby, so the ground beneath a walnut is far from barren.
Walnuts are a safe, healthy snack for dogs.
A plain kernel will not poison a dog, though its richness can upset the stomach and a whole nut can choke or block the gut. The true hazard is a moldy walnut, 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 come true. A seedling is a gamble, yielding variable nuts and waiting many years to bear.