Tree · Juglandaceae
Walnut
Juglans regia
Give it deep soil, full sun, and space to stretch out, and a walnut will shade the yard for generations while filling 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 that people grow for the nuts just as much as for the way it anchors a yard. It's part of the walnut family, climbs to about 60 feet (18 m), and spreads a wide, open crown, so it really does need a spot to itself. Give it deep, fertile soil and full sun, and it'll crop and shade for generations.
The English or Persian walnut is the one most folks plant for the kernels, and its tougher cousin, the native black walnut, brings hard-shelled nuts and dark timber. Here's the catch: both make a compound called juglone that leaks from the roots and hulls and holds back a few sensitive plants nearby. So it pays to think about where the tree goes and what you tuck underneath it.
If there's one thing a walnut asks for, it's patience. A grafted tree takes a few years to start bearing, and those falling nuts with their staining hulls? They'll make a mess of any paving below. Plant it well away from the house and walks, though, and you get years of shade and a harvest every fall.
Care
The short version: full sun and deep, well-drained loam are what it wants, with deep watering while it's young and just the occasional soak once it's settled. Feed it in early spring, prune in late summer so it doesn't bleed sap, and leave it plenty of elbow room.
Light
Walnuts want full sun to crop well, and they'll only put up with light partial shade. Crowd one against buildings or bigger trees and it'll grow lopsided and set way fewer nuts, so give it open sky all around.
Water
Water young trees deeply every 1 to 3 weeks for those first few seasons to help the roots settle. Once it's established, a walnut shrugs off dry spells pretty well, but it still sets the biggest crop if you give it a good deep soak now and then through a dry summer.
Soil
Go for deep, fertile, well-drained loam. A pH of 6.0 to 7.5 is just right, and the one thing it won't stand is wet feet, so skip any waterlogged or shallow ground where the roots can't get going.
Temperature
A walnut is tough and takes a big range, from around -22°F to 95°F (-30°C to 35°C). The tricky part is timing, since a late spring frost can nip the young growth and catkins, which is why later-leafing cultivars have the edge where it gets cold.
Humidity
Everyday outdoor humidity of 40% to 70% is no problem at all for a walnut. What does matter? Damp, still air in a wet spring feeds blight, so an open canopy that dries fast counts for more than any number on a gauge.
Feeding
Feed in early spring before the growth flush, with a nitrogen-focused balanced fertilizer guided by a soil or leaf test. Walnuts are hungry for nitrogen, but test first instead of guessing, because the extra just washes away anyway.
Pruning
Train a young tree to a single central leader, then thin out the dead, crossing, and low limbs as it grows. Do it in late summer or early fall, not late winter, since that's when a walnut bleeds sap heavily from any cut.
Repotting
A walnut is a landscape and orchard tree, not really a pot plant, so once it's in the ground there's no repotting to think about. Hold a young one in a nursery pot too long, though, and you'll see roots circling the pot and stalled top growth, which means it's time to plant it 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). Keep it well clear of buildings, walks, and other trees so the crown has room and those staining nuts don't land on paving.
When to plant
A walnut goes by the calendar, and it likes to be planted while it's still dormant. Pop bare-root or balled trees in the ground in late winter to early spring, look out for the wind-pollinated catkins come spring, and pick the ripe nuts in fall once the hulls start to 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 turns up on the nuts in summer or the leaves as fall rolls in. Spot a pest or a blight early and you can still save that year's crop, so why wait? Find what matches below, then step in while it counts.
Black, slimy husks with maggots inside
Those black, slimy husks with maggots? That's the walnut husk fly, whose grubs feed in the husk and stain the shell as the tissue rots. Get yellow sticky traps up by June, and once you're catching flies steadily, spray a bait insecticide. Then rake up and destroy the fallen, infested nuts so the flies can't come back 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 in the entry holes and nuts dropping early
See frass around a little entry hole and nuts falling too soon? Codling moth larvae have bored straight into the kernels. Set pheromone traps in mid-March, follow degree-days to time your sprays after biofix, and maybe try mating disruption across the orchard. Clearing the infested drops and mummies keeps the next batch from taking hold.
Fix:
- Use pheromone mating disruption in the orchard
- Time insecticide sprays by degree-day models after biofix
- Remove infested drops and mummies
Young nuts turning black and oily when spring stays wet
Greasy black spots on young nuts, leaves, and shoots after a wet, mild spring usually mean walnut blight, a bacterium that can drop a big chunk of the crop. Time your copper-based bactericide sprays with a leaf-wetness model, and keep the canopy open so it dries quickly. Picking a later-leafing cultivar helps you skip the wettest stretch too.
Fix:
- Apply copper-based bactericide sprays timed by a wet-weather model
- Improve air movement and avoid overhead wetting
Blotchy, yellowing foliage that starts falling before autumn arrives
Dark, angular spots that turn into early leaf drop? That's usually anthracnose and its leaf-spot relatives, worse after a wet spring or a drought-stressed summer. Rake up and destroy the fallen leaves to knock back the spores that overwinter. And water deeply through dry spells so the tree stays strong enough to shake it off.
Fix:
- Rake and destroy fallen leaves to reduce inoculum
- Water deeply during dry spells to limit stress
Toxicity
The shelled nuts are great to eat and totally fine for people, but the rest of the tree needs a little care. The wood and shavings carry juglone and cause laminitis in horses, and a moldy fallen nut can bring on tremors and seizures in dogs. So 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 isn't going to poison a cat, though all that fat can still bring on vomiting and a loose stomach. Keep any fallen or moldy nuts out of reach, because the mold on a walnut carries the same toxins that set off tremors.
Dogs Caution
Plain kernels aren't systemically toxic, but a whole nut can choke a dog or get stuck in the gut, and the fat by itself often causes vomiting. The big worry is a moldy walnut off the ground, which can bring on muscle tremors and seizures within hours.
Horses Severe
Walnut shavings used as bedding cause laminitis. Keep an eye out for a reluctance to move, swollen lower limbs, heat in the hooves, and a pounding digital pulse, sometimes within a day of contact, and never let walnut wood or sawdust near a stable.
Rabbits Caution
Walnuts just don't belong in a rabbit's diet. That rich, fatty kernel can throw off a gut built for grass and hay, so keep the nuts and hulls well away from any hutch.
Livestock Caution
Grazing animals are better off kept away from 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 bit of plain kernel is fine for some birds, but the fat adds up fast and a moldy nut is dangerous. Stick to fresh, unspoiled pieces and clear away anything that's fallen and started to rot.
People Shelled nuts safe
Shelled walnuts are a wholesome food and perfectly safe to eat. Just 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
Just a few walnut cultivars cover most home and orchard plantings, and these are the ones worth knowing by name.
'Chandler'
'Chandler' is a top lateral-bearing English walnut that folks love for big yields of light, clean kernels, and since it leafs out late, it dodges most of the spring frost.
'Franquette'
'Franquette' is a late-leafing French cultivar that bears on its terminals and pulls double duty as a handy pollinizer on cooler, frost-prone sites.
Black walnut (Juglans nigra)
Black walnut is the native North American species with darker, hard-shelled nuts and prized timber, and it's the main source of juglone, which is toxic to horses, plus the usual rootstock under English walnut.
'Carpathian'
'Carpathian' is a cold-hardy strain of English walnut that's tough enough to make it through winters down to about 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 get grafted when you want a known crop, or grown from seed when the nut itself is the whole point, though seed is slow going 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
Just about every named walnut starts out 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 those roots hand over, and the young tree needs roughly 4 to 7 years to give a real 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 easy enough, just slow and a bit of a wildcard. Cold-stratify the nuts for about 90 to 120 days and sow in spring, or plant stratified nuts straight into fall ground. The seedlings won't match the parent cultivar and can take 8 to 12 years or more to bear, so most end up as rootstock for grafting.
Myths
Nothing can survive in the ground around a walnut tree.
Sure, the tree gives off juglone, and it does hit sensitive plants like tomato, potato, apple, and blueberry, but mostly inside the drip line. Loads of plants tolerate juglone and grow just fine nearby, so the ground under a walnut isn't a dead zone.
Dogs can snack on walnuts without any worry.
A plain kernel won't poison a dog, but it's rich enough to upset the stomach, and a whole nut can choke or block the gut. The real trouble is a moldy walnut, since its mycotoxins bring on tremors and seizures.
A walnut grown from a nut turns out just like its parent tree.
Named English walnuts are grafted onto black walnut or Paradox rootstock, so the seed inside a nut just won't breed true. A seedling's a gamble, growing variable nuts and taking many years to bear.