Honey locust trees have a graceful appearance. Their leaves are composed of many small leaflets and turn brilliant yellow in autumn. (Honeylocusts leaf out late in spring and drop their leaves early in autumn.) The blooms are insignificant, but give way to large, twisted seed pods that look something like flattened beans. While some varieties are largely thornless (there may be some errant thorns here and there), others are not.
- Common name: Thornless honey locust
- Botanical name: Gleditsia triacanthos var. inermis
- Zones: 3 to 7
- To 90 feet tall and 75 feet wide
- From: Areas of North America
- Family: Fabaceae (pea family)
- Sun: Full sun
- Soil: Moist, but well-drained soil is best. They are adaptable to many soils, but avoid heavy clay or heavily compacted soils.
- Moisture: The trees are drought tolerant, though a bit of additional moisture during times of drought is helpful.
- Mulch: A layer of mulch around the base of the tree is helpful in conserving moisture and reducing competition from turf and weeds. It also protects the tree's trunk from damage from lawnmowers. The mulch should be 2 to 3 inches deep and kept at least 4 inches from the tree's trunk.
- Pruning: Prune out dead or diseased wood anytime. If pruning healthy branches is necessary, do so in early winter.
- Fertilizer: Unnecessary in most soils.
- Seed: Scarify or soak seed for 24 hours in warm water before planting. The seeds prefer cold temperatures (around 32F) for several months before germinating.
- Aphids: These small insects often appear in large numbers on new growth. Spray them off daily with a stream of water; they will not attack a plant after being knocked off. Use an insecticidal soap or neem-oil-based spray if infestations are severe.
- Borers: These insects bore tunnels beneath the bark. You might see small holes with sawdust beneath them. To deter borers, encourage beneficial insects and use horticultural oil while the trees are dormant.
- Canker: Forms dark water-soaked cankers on the bark and branches of the tree. The cankers can spread, becoming larger. To deter the disease, prune off any infected branches, dipping your pruning tool in a bleach or alcohol solution between cuts.
- Powdery mildew: This disease tends to appear in mid- to late summer and looks like someone dusted affected leaves with a grayish powdery covering. The leaves then drop off. To deter the disease, prune the plant to keep good air flow and avoid wetting the foliage in afternoons and evenings.
- Honeylocusts bear hanging seedpods in autumn. As they fall from the tree, they can be messy.
- The pods may attract wildlife.
- Gleditsia triacanthos var. inermis ‘Emerald Kascade': This cultivar has a weeping habit.
- Gleditsia triacanthos var. inermis ‘Halka': A cultivar to 50 feet tall with fewer to no seedpods.
- Gleditsia triacanthos var. inermis ‘Imperial': A compact cultivar to 35 feet tall with fewer seedpods.
- Gleditsia triacanthos var. inermis ‘Limelight': Said to be an improved form of ‘Sunburst', this tree grows 35 feet tall and wide and has golden foliage that fades to pale green in summer.
- Gleditsia triacanthos var. inermis ‘Rubylace': A compact cultivar to 45 feet tall with reddish-purple new growth. It's said to be more susceptible to weather damage than other cultivars.
- Gleditsia triacanthos var. inermis ‘Shademaster': A selection that grows to 45 feet tall with a more upright habit than the species.
- Gleditsia triacanthos var. inermis ‘Skyline': This cultivar grows to 50 feet tall and has a more compact habit than the species.
- Gleditsia triacanthos var. inermis ‘Sunburst': A quick-growing honey locust with golden foliage as it emerges; the foliage fades to pale green. To 40 feet.