Black walnut
Juglans nigra
also called american walnut, eastern black walnut
The native walnut: a huge, valuable, long-lived nut and timber tree with a rich, wild-tasting crop, and a chemical shadow underneath it that decides what the rest of the garden can be.
- Type
- Tree · Perennial
- Botanical family
- Mixed / other
- Foliage color
- Green
- Flower color
- Green
- Sunlight
- Full sun
- Watering
- Moderate
- Soil
- Deep, rich, moist, well-drained
- Feeding
- All-purpose balanced
- USDA zones
- 4a–9a
- Frost tolerant
- Yes
- Plant out
- 30 days before the last spring frost
- First harvest
- 240 days after the last spring frost
- Harvest ends
- 30 days after the first fall frost
- Plant spacing
- 49 ft 3 in
- In-row spacing
- 39 ft 4 in
- Between rows
- 59 ft 1 in
- Square-foot density
- Not suited to SFG
- Sow depth
- 2 in
- Root system
- Woody, with a taproot it keeps
- Working depth
- 24 in–5 ft
- Can reach
- 10 ft down where the soil allows
- Spread
- 98–164 ft across, about 1.5–2.5× the width of the plant
It anchors downwards as well as sideways, which is what lets it stand in a gale and what makes it hate being moved. Plant it small: past a few years in the ground a taprooted tree transplants badly, and often not at all.
The most notorious juglone producer of the lot. Tomatoes, potatoes, peppers, apples, blueberries, rhododendrons and lilacs will not grow within the root zone, which extends well past the branch tips and stays poisoned for years after felling.
The habit is Black walnut’s own; the figures are what that habit usually comes to at this size, not a measurement of this species. Roots follow the soil either way: a compacted pan, a high water table or heavy clay stops them well short of any of it, and deep open ground lets them go further.
- Cats
- Confirmed safe
- Dogs
- Recorded toxic
Recorded non-toxic to cats by ASPCA.
Recorded as toxic to dogs by ASPCA.
We say a plant is safe only where a named poison-control reference names that exact species and records it as non-toxic to both cats and dogs. Most plants are on nobody’s list, and their absence here is not a judgement about them. This is a record of what those references say, not veterinary advice, and it cannot account for your own animal, the quantity eaten, or a plant treated with anything.
The strongest divergent row in the file: one source, one entry, cats on its non-toxic line and dogs on its toxic line. Not an absence on one side but an opposite finding, which is why the card names the two animals on separate rows with their own attributed sentences.
- When
- Nuts from late September, when they thud down green; get them up within days.
- What to look for
- Husks yellow-green and yielding slightly. On the ground a week, the husk blackens and the stain goes into the kernel.
- How to harvest
- Wear old clothes and rubber gloves; the stain defeats soap. Stomp or roll the husks off, wash the nuts, then dry them in shell somewhere airy for two weeks before cracking, which takes a vise, a hammer or the proper cracker; a nutcracker from the kitchen drawer will lose.
- How often
- Daily pickups through the drop, racing the squirrels.
- Storing the crop
- Cured nuts keep a year in shell somewhere cool; shelled kernels go rancid at room temperature, so freeze them. The hulls dye anything they touch a permanent brown, which crafters count as a second harvest.
- Caterpillars Walnut caterpillars stripping single branches in late summer
- Squirrels Squirrels taking the whole crop the week before you meant to
- Thousand cankers disease Thousand cankers disease, spread by walnut twig beetles in the West; do not move walnut firewood
- Black walnut toxicity Juglone beneath it: not a pest of the tree but of the tomatoes planted inside its root run
Beneficial predators that hunt this plant's pests — grow their favourite flowers nearby to recruit them. companion plant
- Assassin bug ReduviidaeHunts Caterpillars
A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be.
- Bats ChiropteraHunts Caterpillars
A single bat takes hundreds of moths and mosquitoes in a night, and the moths are the parents of your cutworms, corn earworms and hornworms. Put up a bat box on a warm south wall, leave a night-scented corner unlit, and never spray after dark.
- Big-eyed bug Geocoris spp.Hunts Caterpillars
A stubby 3 mm bug with enormous wrap-around eyes, working the soil surface and the low foliage for aphids, mites, thrips and insect eggs. It is the main natural check on chinch bugs in a lawn and it is killed outright by insecticide.
- Damsel bug NabidaeHunts Caterpillars
A slender, mantis-armed bug that grabs aphids, small caterpillars, and thrips in low crops and meadowy edges. Leave a strip of unmown grasses and flowers for it to overwinter in.
- Garden birds PasseriformesHunts Caterpillars
Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray.
- Green lacewing Chrysoperla carneaHunts Caterpillars
Its bristly larvae — "aphid lions" — impale aphids, mealybugs, thrips, and mite colonies, eating hundreds a week. Adults feed on nectar and pollen from small open flowers and overwinter in hollow stems left standing.
- Hedgehog Erinaceus europaeusHunts Caterpillars
A European animal, and worth saying so plainly: there are no hedgehogs in North America, and the ally that does the same night shift here is the toad, the opossum or the ground beetle. Where they do occur, cut a gap in the fence and skip the pellets.
- Minute pirate bug Orius spp.Hunts Caterpillars
A pinhead-sized true bug that is the best natural check on thrips, and happily spears aphids, mites, and insect eggs too. It needs pollen when prey is scarce, so keep something flowering nearby.
- Parasitic wasps Braconidae & TrichogrammaHunts Caterpillars
Tiny, stingless wasps that lay eggs in or on caterpillars, aphids, and moth eggs — the white cocoons riding a hornworm are their calling card, so leave that caterpillar be. Umbel flowers with shallow nectar keep the adults fuelled.
- Praying mantis MantidaeHunts Caterpillars
A sit-and-wait ambusher that snatches caterpillars, beetles, and anything else that wanders close — friend and foe alike, so count it a mixed blessing. Tall, structured plantings give it perches and egg-case anchors.
- Snakes & lizards Colubridae & PhrynosomatidaeHunts Caterpillars
A garter snake works the beds for slugs and voles and a fence lizard clears grasshoppers off a sunny wall. Almost every snake a gardener meets is harmless and useful; give them a log pile, a warm flat stone and a bit of cover and they stay.
- Soldier beetle CantharidaeHunts Caterpillars
Soft-winged beetles seen mating on flower heads in high summer; adults and larvae both take aphids and soft grubs. Open composite flowers are their landing pads and hunting grounds.
- Spiders AraneaeHunts Caterpillars
Webs, ambushes, and night patrols make spiders the garden’s steadiest generalist predators, taking whatever flies or crawls past. Mulch, ground cover, and undisturbed corners keep the population dense.
- Spined soldier bug Podisus maculiventrisHunts Caterpillars
A predatory stink bug — same shield outline as the pest, but with a sharp spine at each shoulder and a beak it uses to spear caterpillars and beetle grubs. Learn the spines before you squash a shield bug, because this one is on your side.
- Tachinid fly TachinidaeHunts Caterpillars
Bristly, house-fly-lookalike parasitoids that lay eggs on caterpillars, beetle grubs, and earwigs — the maggot consumes the host from within. Adults sip nectar from shallow umbels and daisies.
Veneer buyers walk farms looking for good ones: a single straight trunk can be worth thousands of dollars standing. Plan the garden around the juglone: tomatoes, peppers, apples and blueberries fail within its root zone, while beans, corn, squash and most natives do not mind it.
The Cottage Garden Companion — the gardener's herbarium at cottagegardencompanion.com