Introduction

`Skyline' Honeylocust grows quickly to 50 feet or more with a rounded canopy comprised of several dominant ascending branches. Young trees may be more pyramidal with a central trunk. A central leader usually develops with little encouragement and the tree will require little pruning. This makes the tree well suited for street tree planting since lower branches can be removed without deforming the nice shape of the crown. The species has undesirable thorns on the trunk and main branches and large seed pods but this cultivar is almost seedless. The tree is strong-wooded and casts light shade. Lawns grow fairly well beneath the tree and there is little to rake up in the fall since the tiny leaflets filter in between the blades of grass or are washed away in the rain. Honeylocust has a yellow or golden fall color in the northern part of its range. Trees often defoliate early in the south and are bare by October.

General Information

Scientific name: Gleditsia triacanthos var. inermis

Pronunciation: gleh-DIT-see-uh try-uh-KANTH-oase variety ih-NER-miss

Common name(s): 'Skyline' Thornless Honeylocust

Family: Leguminosae

USDA hardiness zones: 4A through 8A (Fig. 2)

Origin: native to North America

Invasive potential: little invasive potential

Uses: urban tolerant; street without sidewalk; shade; specimen; parking lot island > 200 sq ft; sidewalk cutout (tree pit); tree lawn > 6 ft wide; highway median; reclamation

Availability: not native to North America

Description

Height: 50 to 75 feet

Spread: 35 to 50 feet

Crown uniformity: symmetrical

Crown shape: pyramidal

Crown density: moderate

Growth rate: fast

Texture: fine

Foliage

Leaf arrangement: alternate (Fig. 3)

Leaf type: bipinnately compound, odd-pinnately compound

Leaf margin: crenate

Leaf shape: oblong, lanceolate

Leaf venation: pinnate

Leaf type and persistence: deciduous

Leaf blade length: less than 2 inches

Leaf color: green

Fall color: yellow, copper

Fall characteristic: showy

Flower

Flower color: yellow

Flower characteristics: not showy

Fruit

Fruit shape: no fruit

Fruit length: no fruit

Fruit covering: no fruit

Fruit color: no fruit

Fruit characteristics: no fruit

Trunk and Branches

Trunk/bark/branches: branches droop; not showy; typically one trunk; thorns

Pruning requirement: little required

Breakage: resistant

Current year twig color: brown

Current year twig thickness: thin

Wood specific gravity: unknown

Culture

Light requirement: full sun, partial sun or partial shade

Soil tolerances: sand; loam; clay; acidic; alkaline; occasionally wet; well-drained

Drought tolerance: high

Aerosol salt tolerance: high

Other

Roots: can form large surface roots

Winter interest: yes

Outstanding tree: no

Ozone sensitivity: unknown

Verticillium wilt susceptibility: resistant

Pest resistance: resistant to pests/diseases

Use and Management

The tree has no particular soil preferences and is useful in dry or alkaline areas, although its native habitat is along stream banks. It tolerates compacted, poorly aerated soil and flooding for a period of time and does well in confined soil spaces. Honeylocust adapts well as a city street tree and is tolerant to small planting pits in concrete. Unfortunately, it has been overplanted in some areas and insect problems are beginning to catch up with Honeylocust, including the cultivars. Recommend planting only small numbers of this tree to avoid catastrophe if insects or diseases invade. It might be best to plant Pistacia, Zelkova, Taxodium, Quercus, or some other proven urban tough tree in place of Honeylocust to avoid potential insect, disease and early defoliation problems in the deep south.

Most garden centers will have at least one cultivar of Honeylocust in stock. Some of the cultivars may develop thorns and/or seed pods when they get older and they may be best suited for areas north of USDA hardiness zone 8b. The cultivars are: `Cottage Green' - semi upright, seedless, thornless; `Imperial' - spreading, seedless, and thornless until 10 to 15-years-old when some seeds do develop; `Majestic' - upright, seedless, thornless; `Maxwell' - upright, seedless, thornless; `Moraine' - spreading, usually seedless, thornless; `Rubylace' - new reddish foliage, seedless, thornless, color not outstanding, may need staking when young; `Shademaster' - upright, spreading, usually seedless and thornless until 10 to 15-years-old when some seeds do develop - perhaps the best cultivar; `Skyline' - pyramidal in youth, generally seedless, thornless; `Sunburst' - new yellow foliage, seedless, thornless, favored by plant bugs and leafhoppers.

Pests

Mimosa webworm has become a serious pest on Honeylocust in some communities.

Boring insects may be largely prevented by keeping trees healthy with regular fertilization. They usually attack trees under stress from other problems.

The combination of plant bug and leafhopper feeding causes the leaves to drop. Plant bugs may be more common on the yellow leaved cultivar `Sunburst' than on green leaved types. Both insects are green so they will be hard to detect.

Pod gall midge causes unusual reddish galls at the tips of the branches. Leaflets become pod-like. The galls appear in late spring and may be most common on thornless, seedless cultivars. These have become quite a problem in many areas. Control is difficult.

Spider mites cause an autumn-like yellowing of the leaves. Diagnosis of this problem is difficult due to the small size of the insect and leaflets. Look for the mites and their webbing near the midrib at the base of the leaflets.

Leafminers and bagworm can also be a problem.

Diseases

Canker causing fungi or bacteria attack branches and trunks causing dieback of parts or the entire tree. Keep the trees healthy and avoid unnecessary wounding. Infected areas have discolored bark, peeling bark, discolored sapwood, or a crack between the diseased and healthy bark. The ronectria canker is especially damaging.

There is a leaf spot may be a problem. Rake up and dispose of infected leaves.

Powdery mildew may cause a white coating on the leaves but is seldom serious.