In short
- A fast-growing tree reaching 12-20 m in height in cultivation.
- The airy crown lets through plenty of light, so a lawn survives beneath the tree.
- Exceptionally tolerant of drought, salinity and urban pollution.
- The typical species has branched thorns and large pods; cities plant thornless cultivars (inermis).
- The fine, pinnate leaflets turn a golden yellow in autumn and decompose quickly, without smothering the lawn.
Botanical data
- Family
- Fabaceae (Fabaceae)
- Height
- 12–20 m
- Width
- 8–15 m
- Habit
- Spreading
- Growth rate
- Fast
- Position
- Full sun
- Soil
- Loamy, Sandy, Chalky
- pH reaction
- pH 6–8
- Moisture
- Dry, Moderate
- Bloom
- May–June
- Hardiness
- USDA 4a–9a
- Propagation
- From seed, From cuttings
Characteristics
A large tree with a straight or slightly leaning trunk and a broad, flattened, loose crown through which the sky shows - hence the popular description "airy". The leaves are pinnately compound, often doubly pinnate on young shoots, made up of numerous small, oblong leaflets 1-3 cm long; bright green and glossy in spring and summer, they turn clear golden yellows in autumn. Because the delicate foliage breaks apart into many small segments, the fallen leaves decompose quickly and do not form a dense layer on the lawn. The flowers are inconspicuous, greenish to cream, gathered in narrow, hanging racemes; they open at the turn of May and June and give off a faint, sweetish scent that lures insects. The fruit is a long, flattened, often spirally twisted pod reaching 20-40 cm, changing colour from green to dark brown; inside, a sweetish, sticky pulp lies between the seeds. The most characteristic feature of the typical species is its thorns: hard, often triply or multiply branched, growing directly from the trunk and older limbs and reaching more than ten centimetres in length. The bark is grey-brown, cracking on older trees into long, peeling strips. The root system is deep and strong, which further increases the tree's resistance to drought and wind.
Popular cultivars
- ‘Sunburst’
- The most popular ornamental cultivar (trade name Suncole), thornless and seedless. The young growth is bright yellow and brightens the crown all summer long, greening with age; it reaches about 10-12 m.
- ‘Skyline’
- Thornless and seedless, with a regular, broadly conical to pyramidal crown and a distinct leader. Valued as an orderly street tree; leaves golden yellow in autumn.
- ‘Shademaster’
- A vigorous, thornless and seedless cultivar with ascending limbs and a crown denser than the species, giving more shade. Dark green leaves persist long into autumn.
- ‘Ruby Lace’
- A thornless cultivar with young leaves coloured bronze-red to purple, greening in summer. Planted for its colour effect; grows more weakly than green-leaved cultivars.
- ‘Moraine’
- One of the first thornless and seedless cultivars introduced to the trade, with a broad, spreading crown and good resistance to difficult urban conditions.
- ‘Imperial’
- A thornless cultivar (trade name Impcole) with a compact, symmetrical, rounded crown and moderate size, which is why it is sometimes chosen for smaller urban and residential spaces.
Growing and care
Watering
Once established, exceptionally drought-resistant and tolerant of short-term soil salinity; only young, freshly planted specimens require regular watering through the first two or three seasons.
Fertilizing
On average soil, fertilizing is usually unnecessary; young trees in poor, urban ground will do with a spring dose of compost or a multi-component fertilizer.
Planting
Tolerates a wide spectrum of soils, including poor, alkaline and compacted urban ground; a sunny, airy site and the absence of permanent standing water are key.
Pruning
Formative pruning of young trees: selecting a leader, removing competing shoots, narrow forks and crossing branches, and raising the crown on street trees.
Companion plants
Good companions
Ażurowa korona przepuszcza dużo światła, dlatego trawnik pod glediczją utrzymuje się lepiej niż pod drzewami o gęstym ulistnieniu.
Rozproszony cień i drobne, szybko rozkładające się listki nie zagłuszają runa, co pozwala obsadzić przestrzeń pod drzewem roślinami znoszącymi pełne słońce lub jasny półcień.
The evidence level indicates whether the relationship is backed by research, observation, or gardening tradition.
Toxicity
| For whom | Level | Notes |
|---|---|---|
| Humans | None | — |
| Dogs | None | — |
| Cats | None | — |
History and origin
The honey locust grows naturally in the moist river valleys and floodplain forests of the central and eastern United States, yet in cultivation it is prized above all for the opposite quality - its endurance of extremely dry, urban conditions. The genus Gleditsia commemorates Johann Gottlieb Gleditsch, the eighteenth-century director of the Berlin botanical garden, while the specific epithet triacanthos means "three-thorned" and refers to the branched thorns. In the old economy of North America the sweet pods were used as fodder for cattle and horses, and the hard wood for posts and tools. The spread of the species in European and American urban horticulture came only in the twentieth century, however, together with the selection of thornless and seedless cultivars from the botanical variety inermis ("unarmed"). It was these - stripped of dangerous thorns and not littering pavements with pods - that made the honey locust one of the most frequently planted street trees, especially as it tolerates the salinity of winter road de-icing, compacted ground and reflected urban heat well.
Uses
The primary use of the honey locust is urban greenery: a street, park and housing-estate tree, planted where tolerance of drought, salinity, compacted soil and pollution matters, while at the same time a light, undemanding shade is desired. The airy crown lets through plenty of light, so lawns and perennials beneath the tree grow better than under species with dense foliage, and the fine autumn leaflets require no laborious raking. For public plantings and home gardens, only thornless and seedless cultivars of the inermis group are chosen - free of dangerous thorns and troublesome pods - such as the yellow-leaved 'Sunburst' or the green, vigorous 'Skyline' and 'Shademaster'. The site should be sunny and airy; the species tolerates poor, calcareous and periodically dried-out soils, but copes badly with permanent waterlogging. It is planted in autumn or early spring, keeping the wide spacing appropriate for a broad-crowned tree. Young specimens are trained by selecting a leader and raising the crown, to gain clearance above the pavement or roadway. The honey locust is not suited to clipped hedges or to small gardens, where the tree's eventual size would quickly become a problem.
Trivia
- Despite belonging to the legume family, the honey locust does not produce root nodules with nitrogen-fixing bacteria and - unlike most legumes - does not enrich the soil with that element.
- The name "honey locust" comes not from bees but from the sweet, honey-like pulp filling the ripe pods.
- The thorns of the typical species can be branched like miniature antlers and grow straight out of the trunk; the inermis cultivars planted in cities are entirely free of them.
- In the names of commercial cultivars the botanical variety var. inermis means "without thorns" - the same element inermis appears in the names of many other plants that are armed in the wild but whose garden forms have been stripped of spines.
Frequently asked questions
Does the honey locust have thorns and is it safe near the house?
The typical species is armed with long, branched thorns on the trunk and limbs, which is why only thornless cultivars of the inermis group (e.g. 'Sunburst', 'Skyline', 'Shademaster') are planted near houses and pavements. When buying a tree, it is worth making sure it is indeed a thornless cultivar and not a seedling of the species.
Will the honey locust survive a Polish winter?
Yes. The species is very frost-hardy - it grows in USDA zones 4a-9a, so throughout Poland it overwinters in the ground without protection. It also tolerates winter road salt well, which is why it works as a street tree.
Why does grass grow better under a honey locust than under other trees?
The crown of the honey locust is airy and lets through plenty of light, and the fine, pinnate leaflets decompose quickly in autumn without forming a dense layer. As a result the lawn and perennials beneath the tree receive more sun and are not smothered by leaves.
How fast does the honey locust grow and how large will it get?
It is a tree that grows fast when young, reaching in cultivation usually 12-20 m in height and 8-15 m in width. Because of its eventual size and broad crown it is not suited to small gardens.
Are honey locust pods poisonous?
They are not classified as a toxic plant, and the sweet pulp from the pods was once fed to livestock. The main nuisance is the pods themselves littering the pavement and lawn, along with the hard thorns of the typical species - which is why cities plant seedless and thornless cultivars.
Sources
- Plants of the World Online (POWO) — Gleditsia triacanthosDatabase (GBIF, POWO…)
- RHS — Gleditsia triacanthosInstitution / botanical garden
- Missouri Botanical Garden — Gleditsia triacanthosInstitution / botanical garden
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