Tree · Anacardiaceae
Cashew
Anacardium occidentale
One generous tropical tree, two harvests in a single season, the cashew apple and the nut, as long as its roots stay warm, sunny, and well drained.
Full sun
Every 7–14 days
USDA 10–13
20–39 ft · 6–12 m
Overview
This is a quick-growing tropical tree, a cousin of poison ivy and mango, native to the warm lowlands of Brazil and now planted across the frost-free tropics. It craves real heat and cannot stand cold, so it lives only in the warmest zones where frost never arrives. Given space, it stretches into a wide spreading tree that can reach 40 feet (12 m) with a canopy just as broad.
What dangles from the branches puzzles a lot of people at first. The plump red or yellow part everyone spots is the cashew apple, a swollen stalk rather than the true fruit, while the kidney-shaped nut hangs below it on the outside. That nut is the prize, yet its shell carries a caustic oil that has to be cooked away before the kernel inside is safe to eat.
For all its size, a settled cashew asks very little of you. It does well in poor sandy ground where pickier trees sulk, and it shrugs off dry spells after the first few years. The one thing it truly will not tolerate is wet feet, so from the very first planting day, drainage matters more than rich soil.
Care
The short version: give your cashew full sun and deep sandy soil that drains fast, water it steadily only while it is young, keep it warm and away from frost, then ease back once it matures. The single thing to avoid is letting the roots sit in soggy ground, and almost everything else it will forgive.
Light
Cashews want full sun and crop poorly in shade. Pick an open, bright spot with nothing crowding the canopy, and all that light keeps the flowers and nuts coming season after season.
Water
Water young trees often so they settle in well, then ease right back, because a grown cashew is highly drought tolerant and dislikes wet ground. Let the top half of the soil dry between drinks, roughly every 7 to 14 days, and when in doubt, lean toward too little rather than too much.
Soil
Plant into deep, well-drained sandy or sandy-loam soil, the kind of poor, low-fertility ground that stumps other trees. A pH of 5.0 to 6.5 suits it nicely, and fast drainage counts for far more than rich earth.
Temperature
This is a true tropical tree, happiest somewhere between 50°F to 104°F (10°C to 40°C) and easily killed by frost. Grow it only where cold never bites, in tropical or frost-free subtropical climates.
Humidity
Cashews enjoy air on the humid side, around 50% to 80%, which fits their tropical home. Keep the canopy open so the leaves dry quickly, since trapped damp is what invites disease in.
Feeding
Feed through the warm growing season with a balanced NPK carrying nitrogen, phosphorus, and potassium, plus a little zinc if your soil runs short of it. For so tough a tree, a single seasonal feeding is plenty.
Pruning
Train a young tree to one strong leader, then thin out dead, diseased, crossing, and low branches. An open canopy lets air move freely through, which is your best defense against the fungal troubles cashews can pick up.
Repotting
A cashew planted in the ground stays put for the long haul, but a container tree needs a larger pot every 2 to 3 years. Keep an eye out for roots circling the pot, water rushing straight through, or growth that seems to have stalled.
Size & spacing
A common cashew grows into a wide tree, 20 to 40 feet (6 to 12 m) tall and nearly as broad, so plan to give it serious room. Place it well clear of buildings, paths, and power lines, since the canopy can spread as much as 33 feet (10 m) across.
When to plant
A cashew lives by the rhythm of the tropics, not a temperate calendar. Start nuts in nursery bags a couple of months ahead, move young trees outside once the soil is warm and frost is no longer a worry, then look for flowers in the dry season and nuts and apples several months after that.
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
Nearly all cashew worries turn up on fresh flushes, flowers, or roots, and damp conditions are usually behind them. The good news is that caught early, most clear up with a fungicide or simply better drainage. Find your symptom below, then step in before it has a chance to spread.
Black sunken spots on leaves and shoots with dying twigs
What you are seeing is anthracnose, a fungus that takes hold when warm weather stays wet and new flushes or flower clusters sit damp for hours. Prune away and destroy the infected shoots, open the canopy for airflow, and apply a labeled fungicide as the tree flushes and flowers. Wide spacing and dry foliage stop most of it before it ever begins, so do not be discouraged if it shows up.
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 barely sets fruit in heavy, waterlogged ground has root rot, not thirst. 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 on a raised mound. A mature cashew handles dry spells with ease, so remember the real danger is roots kept 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 over the flower panicles and young nuts points to powdery mildew, which loves soft new growth during cool, dry flowering spells. Left alone, it drops flowers and small nuts and trims your crop. Dust with sulfur or a labeled fungicide at bloom, snip off the worst-hit panicles, and keep that canopy open.
Fix:
- Apply sulfur or a labeled fungicide at flowering
- Remove badly affected panicles
Toxicity
A roasted, shelled cashew is the safe, familiar snack you already know, but the raw nut is a different story. The shell and the thin layer hugging the kernel hold a caustic oil called CNSL, packed with the same urushiol found in poison ivy, which burns skin and mouth the moment it touches them. Keep raw shells, husks, sap, and prunings well 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 can bring on drooling, vomiting, and loose stools. Worse still, a cat that licks or bites a raw shell can burn its mouth on the caustic oil, so keep both well out of paw's reach.
Dogs Caution
A few stolen nuts usually mean vomiting and diarrhea, and a bigger helping of the fatty kernel can spark painful pancreatitis. Chewing on a raw shell adds urushiol burns to the mouth and skin.
Horses Caution
Horses have no business near raw shells, sap, or prunings, where the same urushiol that scars human skin can blister their lips and mouth. Keep fallen shells and trimmings cleared out of 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 happens to get into dropped shells.
Livestock Caution
Cattle, goats, and sheep can scorch their mouths on the raw shell liquid and upset their stomachs on the oily kernels. Fence your stock away from the tree and rake up shell waste once the harvest is in.
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.
People Roasted nuts safe
Properly roasted and shelled cashews are a wholesome, safe snack. The raw nut and its shell are another matter: 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
Cashews are grouped mostly by size and how soon they bear, and two broad types cover just about everything you are likely to come across.
Common (medium/tall) cashew
The common medium or tall cashew is the traditional plantation tree, a broad spreading giant that climbs to 12 m or more and is slow to begin bearing.
Dwarf precocious cashew (e.g. anao precoce types)
The dwarf precocious cashews, such as the anao precoce types, are compact selections that flower and fruit within a few years and stay small enough to plant closely and harvest with ease.
How to propagate
You can grow a cashew from a fresh nut or clone a tree you already love, and the route you choose shapes how quickly it fruits and how closely it matches the parent.
SeedEasy
Sow fresh viable nuts in the warm season · Germinates in 2 to 3 weeks; bears in about 3 years
Sow fresh, viable nuts in the warm season, picking the ones that sink in water, and seedlings push up in 2 to 3 weeks. Set them straight into the ground or into bags, because the long taproot hates being moved once it forms. Seedlings vary from one another, and a tree raised this way takes about 3 years to start bearing, so a little patience pays off.
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 uniform trees that crop sooner. A softwood, cleft, or veneer graft is the usual choice, and the 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. The wrapped stem needs several weeks to root before you cut it free, and it is used far less than grafting on a commercial scale.
Myths
The cashews labeled raw in stores are genuinely raw, so you can eat any nut straight off the tree.
Those so-called raw cashews were already steamed or heat-treated and shelled before they reached the shelf. A nut taken straight from the tree still carries caustic shell oil, the urushiol and anacardic acid that burn skin and mouth. The takeaway: 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.
That plump, juicy cashew apple is not the true fruit at all but a swollen stalk, an accessory fruit the tree puffs up below the flower. The takeaway: the real fruit is the kidney-shaped nut that hangs outside and beneath the apple, never within it.