Tree · Anacardiaceae
Cashew
Anacardium occidentale
A tropical tree that gives you two harvests in one, the cashew apple and the nut, as long as you keep its feet warm, sunny, and well drained.
Full sun
Every 7–14 days
USDA 10–13
20–39 ft · 6–12 m
Overview
The cashew is a fast-growing tropical tree from the same family as poison ivy and the mango, native to the warm lowlands of Brazil and now grown across the frost-free tropics. It wants real heat and hates the cold, holding on only in the warmest zones where frost never reaches. Given room, it stretches into a wide, spreading tree that can top 40 feet (12 m) with a canopy just as broad.
What hangs from the branches throws most people off. The fleshy red or yellow part everyone notices is the cashew apple, a swollen stalk rather than the true fruit, and the kidney-shaped nut dangles below it on the outside. That nut is the prize, but it comes wrapped in a shell loaded with a caustic oil that has to be cooked off before anyone can eat the kernel inside.
For all its size, the cashew asks little once it settles in. It thrives in poor, sandy ground where fussier trees sulk and shrugs off drought after the first few years. The one thing it will not forgive is wet feet, so drainage matters more than fertility from the day you plant it.
Care
The short version: full sun, deep sandy soil that drains fast, and steady water only while the tree is young. Keep it warm and frost-free, go easy once it matures, and never let the roots sit in soggy ground.
Light
Cashews demand full sun and crop poorly in shade. Give the tree an open, bright spot with nothing crowding the canopy, since plenty of light keeps both flowers and nuts coming.
Water
Water young trees often so they settle in, then back right off, because a mature cashew is highly drought tolerant and resents soggy ground. Let the top half of the soil dry between drinks, roughly every 7 to 14 days, and lean toward too little rather than too much.
Soil
Plant in deep, well-drained sandy or sandy-loam soil, the kind of poor, low-fertility ground that defeats other trees. A pH of 5.0 to 6.5 suits it, and fast drainage matters far more than rich earth.
Temperature
This is a true tropical tree, happiest from 50°F to 104°F (10°C to 40°C) and killed outright by frost. Grow it only where the cold never bites, in tropical or frost-free subtropical climates.
Humidity
Cashews like the air on the humid side, around 50% to 80%, in step with the tropics they come from. Even so, keep the canopy open so the leaves dry out, since trapped damp invites disease.
Feeding
Feed through the warm growing season with a balanced NPK carrying nitrogen, phosphorus, and potassium, and add zinc where the soil runs short of it. A seasonal feeding is plenty for a tree this tough.
Pruning
Train a young tree to a single strong leader, then thin out the dead, diseased, crossing, and low branches. Opening the canopy lets air flow through, which is your best defense against the fungal diseases cashews are prone to.
Repotting
A field-grown cashew stays put for the long haul, but a container specimen needs a larger pot every 2 to 3 years. Watch for roots circling the pot, water running straight through, or stalled growth, all signs it has outgrown its home.
Size & spacing
A common cashew grows into a wide tree of 20 to 40 feet (6 to 12 m) tall and nearly as broad, so give it serious room. Site it well clear of buildings, paths, and power lines, since the canopy spreads as much as 33 feet (10 m) across.
When to plant
The cashew runs on the tropics, not the calendar of a temperate garden. Start the nuts in nursery bags a couple of months ahead, set the young trees out once the soil is warm and frost is no risk at all, and look for flowers in the dry season with the nuts and apples following several months behind.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Seeds sown in nursery bags 2 to 3 months before transplanting in warm climates
- Plant: After all frost danger when soil is warm; tropical and frost-free subtropical regions only
- Harvest: Flowers in dry season; nuts and cashew apples harvested several months later, typically late dry season
Hardiness
USDA hardiness zones: 10–13
Temperature: down to -1°C
Troubleshooting
Most cashew trouble shows up on the new flushes, the flowers, or the roots, and damp conditions are usually behind it. Catch these early and a fungicide or better drainage can turn things around. Match what you see below, then act before the problem spreads through the canopy.
Black sunken spots on leaves and shoots with dying twigs
This is anthracnose, a fungus that takes hold when warm weather stays wet and the new flushes and flower clusters stay damp for hours. Prune out and destroy the infected shoots, open the canopy so air moves through, and reach for a labeled fungicide as the tree flushes and flowers. Wide spacing and keeping water off the foliage stop most of it before it starts.
Fix:
- Prune and destroy infected shoots
- Improve canopy air circulation
- Apply a labeled fungicide during susceptible flushing and flowering
Wilting and scorched leaves in wet, soggy soil
A cashew that wilts and sets little fruit in heavy, waterlogged ground is suffering root rot, not drought. The roots discolor and the trouble shows up right after heavy irrigation or standing water. Improve the drainage, ease off the watering, and on heavy soils plant the tree on a raised mound. A mature cashew shrugs off dry spells, so the real danger is keeping the roots too wet.
Fix:
- Improve drainage
- Reduce irrigation
- Plant on mounds in heavy soils
Grayish-white powder on flowers and tender new nuts
A dusty white film on the flower panicles and young nuts points to powdery mildew, which thrives on soft new growth during cool, dry flowering spells. Left alone it sheds flowers and small nuts and cuts your crop. Dust with sulfur or a labeled fungicide as the tree blooms, cut off the worst-hit panicles, and keep the canopy open so the disease has less to work with.
Fix:
- Apply sulfur or a labeled fungicide at flowering
- Remove badly affected panicles
Toxicity
The roasted, shelled cashew is a safe and familiar snack, but the raw nut is another story. The shell and the layer around the kernel hold a caustic oil called CNSL, rich in the same urushiol that gives poison ivy its sting, and it burns skin and mouth on contact. Keep raw shells, husks, sap, and prunings away from children and pets, and handle them only with gloves.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Caution
The rich, fatty kernel brings on drooling, vomiting, and loose stools. Worse, a cat that licks or bites a raw shell can burn its mouth on the caustic oil, so keep both well out of reach.
Dogs Caution
A few stolen nuts usually mean vomiting and diarrhea, and a larger helping of the fatty kernel can trigger painful pancreatitis. Chewing a raw shell adds urushiol burns to the mouth and skin on top of that.
Horses Caution
Horses have no business near the raw shells, sap, or prunings, where the same urushiol that scars human skin can blister the lips and mouth. Keep fallen shells and trimmings cleared from any paddock.
Rabbits Caution
The caustic shell oil and the heavy, fatty nut are both wrong for a rabbit's gut. Offer neither, and watch for soft stools or a stalled appetite if one gets into dropped shells.
Livestock Caution
Cattle, goats, and sheep can scorch their mouths on the raw shell liquid and sour their stomachs on the oily kernels. Fence stock away from the tree and rake up shell waste after harvest.
Birds Caution
Backyard birds should never get raw shells or husks, since the irritant oil burns soft tissue. A crumb of plain roasted kernel now and then does no harm, but the fat does them no favors either.
People Roasted nuts safe
Properly roasted and shelled cashews are a wholesome snack and safe to eat. The raw nut and its shell are a different matter, since the urushiol they carry is the same irritant as poison ivy and burns skin and mouth, which is why nobody should handle or eat them unprocessed.
Wear gloves when handling raw shells, husks or sap; never let people or pets contact or chew unprocessed nuts. Roasting in the open can release irritant fumes.
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
Cashew growers sort their trees mainly by size and how soon they bear. These two broad types cover most of what you will run into.
Common (medium/tall) cashew
This is the traditional plantation tree, a broad spreading giant that climbs to 12 m or more and takes its time before it starts to bear.
Dwarf precocious cashew (e.g. anao precoce types)
These compact selections flower and fruit within a few years and stay small enough to pack closely together and harvest with ease.
How to propagate
You can raise a cashew from a fresh nut or clone a good tree, and the route you pick decides how soon it fruits and how true it stays to its parent.
SeedEasy
Sow fresh viable nuts in the warm season · Germinates in 2 to 3 weeks; bears in about 3 years
Sow fresh nuts in the warm season, choosing the ones that sink in water, and the seedlings break ground in 2 to 3 weeks. Drop them straight into the ground or into bags, because the long taproot hates being moved once it forms. Seedlings vary from one to the next, and a tree raised this way takes about 3 years to start bearing nuts.
GraftingModerate
Onto vigorous seedling rootstock in warm conditions · Bears in roughly 2 to 3 years
Grafting a chosen clone onto a vigorous seedling rootstock in warm weather gives you trees that are uniform and crop sooner. A softwood, cleft, or veneer graft is the usual route, and the resulting tree bears in roughly 2 to 3 years.
Air layeringModerate
Warm humid growing season · Several weeks to root before severing
Air-layering during the warm, humid growing season makes a clone of the parent tree. The wrapped stem needs several weeks to root before you cut it free, and the method sees far less use than grafting on a commercial scale.
Myths
The cashews labeled raw in the store are truly raw, and you can eat any nut straight off the tree.
Those so-called raw cashews have already been steamed or heat-treated and shelled before they reach you. A nut picked straight from the tree still carries caustic shell oil, the urushiol and anacardic acid that burn skin and mouth. No cashew is safe to eat or handle until it has been roasted and processed.
The fleshy red or yellow cashew apple is the fruit, and the nut grows inside it.
The plump, juicy cashew apple is not the true fruit at all but a swollen stalk, an accessory fruit that the tree puffs up below the flower. The real fruit is the kidney-shaped nut that hangs outside and beneath the apple, not tucked away within it.