Ornamental · Fabaceae
Hyacinth Bean
Lablab purpureus
Give it heat, full sun, and a tall trellis, and hyacinth bean throws purple flowers and glossy pods clear into fall.
Full sun
Every 5–7 days
50–95°F · 10–35°C
90–120 days
Overview
Hyacinth bean is a fast climbing vine grown for show, with spikes of purple or white flowers followed by glossy reddish-purple pods that hold their color until frost. It belongs to the pea and bean family, and in warm climates it lives for years, but most gardeners run it as a summer annual from seed. Given a tall trellis, it can climb well past head height in one season.
The looks are the whole point here. The pods are as ornamental as the flowers, and the vine covers an arbor or fence faster than almost anything else you can sow. It thrives on heat, so it earns its keep through the dog days when other climbers stall.
One thing sets it apart from a true garden bean. The raw mature seeds and pods carry cyanogenic compounds and are toxic eaten raw, safe only after thorough cooking, so this is a plant to enjoy with your eyes more than your fork.
Care
The short version: full sun and real warmth, light well-drained soil kept evenly moist while the vine establishes, a balanced feed that goes easy on nitrogen, and a sturdy trellis to carry the fast, heavy growth.
Light
Hyacinth bean wants full sun, ideally 6 or more hours a day, to flower well and hold its pod color. It tolerates a little afternoon shade, but too much shade trades blooms for leggy growth.
Water
Keep the soil evenly moist while the vine is establishing, then ease off, since an established plant takes some drought. Water deeply during hot, dry spells, and lean toward light, well-drained ground rather than soggy soil.
Soil
Average, fertile, well-drained loam suits it fine, with a pH anywhere from 6.0 to 7.5. It isn't fussy about richness, so good drainage matters more than feeding the soil heavily.
Temperature
This is a heat lover that runs best between 50°F and 95°F (10°C to 35°C) and stalls when it turns cool. Frost kills it outright, so it only goes out once the cold is gone for the year.
Humidity
Ordinary outdoor humidity is plenty, so there's no target to hit. Good airflow does more good than any humidity tweak, since crowded, damp leaves invite leaf spot.
Feeding
Feed monthly through summer with a balanced fertilizer. As a legume it fixes its own nitrogen, so go light on high-nitrogen feeds, which push leafy growth at the expense of flowers.
Pruning
Pinch the growing tips early to push the vine into branching, and it needs little cutting after that. Remove spent pods to keep the bloom going, then cut the frost-killed vine back at the end of the season.
Repotting
not typically grown in containers; grown as an annual from seed each year
Size & spacing
Expect a vigorous climber from 10 to 20 feet (3 to 6 m) tall, spreading 3 to 6 feet (91 to 183 cm) across. Give it a sturdy trellis or arbor and room to run so the heavy vine has something to hold.
When to plant
Hyacinth bean runs on heat and dies at the first frost. Sow it outdoors only after the cold has passed and the soil has warmed, or start it indoors 6 to 8 weeks ahead to steal a head start, and it flowers from summer right up to fall frost.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 6 to 8 weeks before the last spring frost
- Plant: after danger of frost has passed and soil is warm
- Harvest: summer to frost (roughly June until first fall frost)
Hardiness
USDA hardiness zones: 10–11
Temperature: down to -1°C
Troubleshooting
Hyacinth bean is tough and shakes off most trouble, with pests doing more damage than disease. Watch the leaves and new growth for the early signs below, and step in before a small problem spreads across the vine.
Speckled, yellowing leaves with faint webbing in the heat
Spider mites move in during hot, dry spells and stipple the leaves with tiny pale dots. Tap a leaf over white paper to catch the specks moving, and look for fine webbing on the undersides. Hose the foliage down to knock them loose and raise the humidity, then use insecticidal soap or horticultural oil if they hang on.
Fix:
- Hose down foliage to dislodge mites and raise humidity
- Apply insecticidal soap or horticultural oil if infestation persists
Stunted vines and few flowers when the weather stays cool
Hyacinth bean is a heat lover, so cool weather leaves it sulking with short vines and little bloom. The same thing happens when seedlings go out before the soil has warmed and the last frost has passed. Wait for warm ground and a sheltered, full-sun spot, and the vine takes off once the temperatures climb.
Fix:
- Wait to plant until soil is warm and frost danger has passed
- Provide a full-sun, sheltered, warm site
Leaves chewed into a lacy, see-through skeleton
This is Japanese beetle damage, and it shows up most in summer when the metallic green-and-copper beetles cluster on the foliage. They eat the soft tissue between the veins and leave a lace-like skeleton behind. Pick them off by hand in the early morning, and don't panic over light feeding, since a fast vine pushes out fresh leaves and shrugs it off.
Fix:
- Hand-pick beetles in early morning and drop them into soapy water
- Tolerate light damage, since vines push out fresh foliage and survive well
Curled new growth that feels sticky to the touch
Tender shoots and flower buds that pucker and turn sticky point to aphids. Check the undersides of young leaves for colonies of small green or black insects and the shiny honeydew they leave behind. Knock them off with a hard jet of water, and reach for insecticidal soap only when a colony gets out of hand.
Fix:
- Spray colonies off with a strong jet of water
- Apply insecticidal soap to heavy infestations
Dark spots on the leaves, sometimes ringed in yellow
Round brown spots that spread in wet, muggy weather are usually fungal leaf spot. The marks stay roughly circular at first and may run together as more leaves get hit. Strip off the worst leaves, water at the base instead of over the top, and give the vine room so air can dry the foliage.
Fix:
- Remove and discard badly affected leaves
- Improve air circulation and avoid overhead watering
Toxicity
Treat the colorful pods as a look-don't-eat plant. The raw mature seeds and pods hold cyanogenic glycosides that are toxic to people and animals alike, and only thorough cooking makes the young pods safe. Keep the glossy pods and seeds away from children, pets, and grazing animals.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Caution
A cat that chews the raw seeds or pods can end up with drooling, vomiting, and a sore stomach from the cyanogenic compounds. Keep the glossy pods out of reach.
Dogs Caution
Dogs are the ones most likely to crunch the colorful pods, and the raw beans can bring on stomach upset, retching, and lethargy. Pick up any fallen pods where a curious dog roams.
Horses Caution
The same cyanide-releasing compounds in raw beans and foliage can leave a horse weak, breathing hard, and off its feed. Fence the vine away from where horses graze.
Rabbits Caution
Raw seeds and pods aren't safe browse for rabbits and can trigger gut trouble and lethargy. Don't offer trimmings from the vine.
Livestock Caution
Cattle, goats, and sheep can suffer cyanide poisoning from large amounts of the raw beans, with staggering, labored breathing, and collapse in bad cases. Keep them off plantings gone to pod.
Birds Caution
Pet and backyard birds shouldn't peck the raw mature seeds, which carry the same cyanogenic glycosides. Stick to feed you know is safe.
People Young cooked pods safe
Young pods are eaten in many countries once they are thoroughly cooked. The raw mature beans are a different story and must be boiled in several changes of water before eating, since raw they release cyanide that can cause nausea, dizziness, and worse. Never eat the raw beans or pods.
Keep the colorful pods and seeds away from children and curious pets; never eat raw mature beans or pods. Only thoroughly cooked beans are safe.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
A few named forms turn up in gardens, set apart mainly by flower and pod color. These are the ones worth knowing.
Ruby Moon
The most widely grown ornamental form, carrying deep purple stems and glossy reddish-purple flat pods that draw the eye all season.
Alba (white-flowered form)
A white-flowered, white-seeded form with plain green pods that skips the purple coloring of the usual type.
How to propagate
Hyacinth bean is grown from seed, and it sprouts fast and climbs faster, so a single packet covers a lot of trellis in one warm season.
SeedEasy
Sow outdoors after frost when soil is warm, or start indoors 6 to 8 weeks before the last frost. · Germinates in roughly 1 to 3 weeks; grows rapidly to cover a trellis in a single season
Grow hyacinth bean from seed each year, sowing outdoors after frost once the soil is warm or starting indoors 6 to 8 weeks before the last frost. Soaking or nicking the hard seed coat speeds the 1 to 3 week germination, and from there the vine races up a trellis in a single season. Set up a sturdy trellis or arbor before it gets going, and save seed in fall to replant next spring.
Myths
It is a bean, so you can eat the pods and seeds raw straight off the vine.
The raw mature seeds and pods hold cyanogenic glycosides and are toxic if eaten raw. Mature beans are safe only after thorough cooking, boiled in several changes of water, and in the US the plant is grown mainly for show rather than the table.