Tree · Fabaceae
Honey Locust
Gleditsia triacanthos
Fine-leaved and fast, the honey locust filters the sun into a soft dappled shade through its lacy canopy.
Full sun
Every 7–14 days
USDA 3–9
30–79 ft · 9–24 m
Overview
The honey locust wears a canopy of small, fine leaflets that break the sunlight into a light, dappled shade thin enough for grass and flowers to grow right up against the trunk. It is a fast-growing legume from central North America, named for the sweet pulp packed inside its long, twisting brown pods. Left wild it rises to 30 to 80 feet (9 to 24 m), its branches fanning out into a broad, open crown of feathery foliage.
In late spring the tree hangs out small, inconspicuous, greenish-yellow flowers that give off a faint sweetness. By September and October those flowers have become flat, twisted brown pods, and the fine foliage of some cultivars flushes golden yellow at the tips. The whole crown holds a soft, airy texture that reads more as filtered light than solid shade.
The wild form is a fiercer thing up close. Its trunk and larger branches bristle with long, branched thorns, hard and sharp, and it drops heavy pods across the ground. Selection stripped both away in the thornless, seedless cultivars of var. inermis, whose bark runs smooth and unarmed, and those are the trees a nursery offers.
Care
The short version: full sun and almost any soil suit the honey locust, regular water carries it through the first couple of years, and once settled it stands among the most drought-tolerant of shade trees.
Light
The honey locust wants full sun to fill out its fine, feathery crown to the fullest. It tolerates part shade, but growth is quickest and the foliage densest out in the open under at least six hours of direct light a day.
Water
A young tree needs a regular soak through its first one to two years as the roots reach out into the ground. After that it turns very drought tolerant and rarely asks for water, so the top half of the soil is left to dry between drinks.
Soil
The honey locust is easygoing about its footing. It grows best in moist, rich loam but takes clay, sand, poor ground, compaction, salt, and alkaline city dirt in stride, across a wide pH band of 6.0 to 8.0.
Temperature
This is a cold-hardy tree built for extremes, comfortable from -40°F to 100°F (-40°C to 38°C). That toughness covers USDA zones 3 through 9 and lets it grow where many shade trees cannot.
Humidity
Outdoor humidity is no issue for an established tree, so there is no level to manage. Good air movement through the open crown does more good, drying the fine foliage and keeping mite and disease pressure low.
Feeding
As a legume, the honey locust largely feeds itself and rarely needs more. Fertilizer stays off unless the soil is genuinely poor, and then a single balanced slow-release dose in spring is enough.
Pruning
Pruning falls in late winter to early spring while the tree is bare and dormant, its branch structure easy to read. A young tree is trained to one strong central leader, with crossing, dead, or damaged wood cut away.
Repotting
The honey locust belongs in open ground rather than a pot, so repotting rarely comes up. A young container tree is moved on once its roots circle the inside or push out the drainage holes.
Size & spacing
This tree needs real room, since it reaches 30 to 80 feet (9 to 24 m) tall and spreads its broad crown 25 to 50 feet (8 to 15 m) wide. Clearance from buildings, walls, and other trees lets the open canopy fill out fully.
When to plant
The honey locust moves through the year in clear stages. It is planted in spring or fall, hangs out small fragrant greenish-yellow flowers in late spring, and drops its long twisted brown pods as they ripen through early autumn.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring or fall
- Harvest: Inconspicuous fragrant greenish-yellow flowers in late spring (May to June); flat twisted brown seed pods ripen September to October.
Hardiness
USDA hardiness zones: 3–9
Temperature: down to -40°C
Troubleshooting
The honey locust is hardy, but a few pests and one serious fungus mark its fine foliage and smooth bark often enough to know on sight. Most of the leaf damage looks alarming yet costs the tree little. The cankers cut deeper, so match what the bark and leaves actually show below before reaching for the saw.
Sunken, discolored patches in the bark with branches dying back
Sunken, discolored patches press into the bark of branches and trunk, often studded with yellow to reddish fruiting bodies, the sign of Thyronectria or Nectria canker. Cut into one and the cambium beneath shows dead and darkened, a fungus that moves in on trees weakened by drought, wounds, or crowding. No spray reverses it, so prune well below each canker in dry weather with disinfected tools, take out a badly cankered tree, and keep the rest strong with steady water and unbroken bark.
Fix:
- Prune out infected branches well below the canker during dry weather and disinfect tools
- Remove and destroy severely cankered trees
- Improve vigor with proper watering and avoid bark wounds
Leaflets wrapped in gray silk and eaten down to their veins by midsummer
Fine gray silk drawn across the leaflets, with small caterpillars wriggling inside, is the sign of the mimosa webworm, which strips golden cultivars such as Sunburst first and worst. The webbed foliage turns thin and brown as the leaflets are chewed down to a lacy skeleton. Cut out the small silk nests early, dab the young caterpillars with Bt, and rake the litter beneath the tree where the pupae overwinter.
Fix:
- Prune out and destroy small webbed nests early
- Apply Bt (Bacillus thuringiensis) while caterpillars are small
- Clean up debris beneath the tree where pupae overwinter
Fat pod-shaped swellings capping the leaflet tips, with tips going bare
The leaflet tips swell into fat, pod-shaped lumps, distorted and thickened, the mark of the honeylocust pod gall midge whose maggots ripen inside. The galled foliage browns and falls early, leaving the fine branch tips bare and stubby. An established tree carries a light case unharmed, but heavy galling calls for horticultural oil on the new tips in March or April and the removal of the worst shoots.
Fix:
- Tolerate light infestations on established trees, which are rarely killed
- Apply horticultural oil to terminals in March-April to kill eggs
- Prune and destroy heavily galled shoots
Crumpled, undersized new leaves in spring
The soft new leaves come out crumpled, dwarfed, and off-color, the work of the small green honeylocust plant bug feeding on them as they unfold. The tree grows past this early damage, so it can be left alone. When the summer heat brings a fine pale stippling and a dusting of webbing to the foliage instead, spider mites are at work, and a hard spray of water or a dose of insecticidal soap knocks them off.
Fix:
- Tolerate minor early-season plant bug damage; trees usually recover
- Hose down foliage to dislodge spider mites
- Use insecticidal soap or horticultural oil for heavy mite outbreaks
Toxicity
For a household with animals, the honey locust is safe. The ASPCA lists it as non-toxic to dogs, cats, and horses, and the sweet pulp of its pods is eaten by livestock and wildlife every fall. The only real hazard is physical, the long sharp thorns that stud wild trunks, which is why landscape cultivars are bred smooth and thornless.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Cats come to no harm. A batted leaflet or a chewed green twig holds no toxin.
Dogs None
Dogs are safe around it. A gnawed brown pod adds coarse roughage but no poison, since the tree carries none.
Horses None
Horses graze near it unharmed, and the sweet, sticky pulp of the pods is a treat rather than a threat.
Rabbits Safe
Rabbits face no poison. The bark and the slim twigs are rough browse and nothing more.
Livestock None
The pods are palatable, nutritious feed rich in sweet pulp. Cattle, goats, and sheep have eaten them without ill effect for generations.
Birds Safe
Birds are safe around it, and wildlife picks the long brown pods clean of their sweet pulp each fall.
People Safe
The sweet pulp inside the ripe brown pods has long been eaten by people. The one real hazard is the wild form's long, branched thorns, so handle a thorny trunk with care.
The wild species bears large, sharp, branched thorns on the trunk and branches that can cause puncture injuries; landscape cultivars are typically thornless.
Varieties
Nearly every honey locust sold for a yard or street is a named thornless cultivar, each with its own crown shape and cast of color. These are the ones seen most.
Shademaster
A vigorous thornless and nearly seedless form that lifts into a vase silhouette on ascending branches, prized as a tough, dependable street tree.
Skyline
A thornless, podless cultivar that holds a tight pyramidal outline around a strong central leader and turns a clean golden-yellow in fall.
Sunburst
A thornless, seedless selection whose new foliage flushes a bright golden yellow at the branch tips, though that same soft new growth draws mimosa webworm and pod gall midge more than any other.
Imperial
A thornless, seedless cultivar that keeps a compact, rounded crown carried on neat horizontal branching.
var. inermis
The naturally thornless botanical form, bare of the branched spines, its name meaning unarmed, and the parent of most landscape cultivars.
How to propagate
A honey locust grows from the flat seeds inside its own pods, but the named cultivars are another matter and must be cloned to hold their thornless, seedless character.
SeedModerate
Spring after collecting ripe pods in fall · 1 to 2 growing seasons to a transplantable seedling
Gather the ripe brown pods in fall and sow the flat seeds in spring, but first nick the hard, waterproof seed coat with a file, hot water, or concentrated sulfuric acid, or the seed stays shut and never sprouts. Give the seedling one to two growing seasons to reach transplant size. A thornless parent does not breed true, since only about 60 percent of the seedlings come up thornless.
GraftingDemanding
Late winter to spring (grafting) or summer (budding) · 1 to 2 growing seasons
Because the named thornless, seedless cultivars never come true from seed, nurseries graft them in late winter to spring or bud them onto seedling rootstock in summer. That holds the exact clone true, and the young tree settles in over one to two growing seasons.
Myths
Honey locust is poisonous to pets and livestock, like the other locust trees.
Honey locust takes the blame meant for the black locust (Robinia pseudoacacia), a separate tree it is easily confused with. Honey locust is non-toxic, and the sweet pulp of its pods feeds livestock and wildlife. It is black locust that carries the toxalbumins that poison dogs and horses.
A honey locust in the yard will grow vicious thorns and drop messy pods.
The wild tree does arm itself with fierce branched thorns and shed long twisted pods, but that is not the tree a nursery sells. Most landscape trees are thornless cultivars of var. inermis, their trunks smooth and unarmed, and many are seedless and podless too.