Thornless Honeylocust (Gleditsia triacanthos var. inermis)
If you work with trees a lot, you’re probably thinking, “Honeylocust? Ugh… really? You’re recommending that tree?”
The groan is understandable. Honeylocust was heavily planted in the late 80s and early 90s; we would say today that the honeylocust was overplanted. The tree is so hardy and tough, though, that it was considered one of the gold-standard urban trees during its heyday.
Arborists have seen the tree frequently fail to perform as well as we’d like in the places we put them. Honeylocust is commonly planted in parking lots and sidewalk cut-outs because the tree will withstand heat, drought, road salt, poor soils, compaction, pollution and mechanical injury. On tough sites honeylocust often exhibit:
- aggressive surface roots;
- stunted growth;
- sickly yellow-green leaves;
- prolific twig and branch dieback;
- watersprouts and sucker growth; and
- increased susceptibility to pest problems such as the Honeylocust pod gall midge.
Despite all this, however, the tree can be remarkably persistent, despite looking so badly for years; it just refuses to die.
No wonder folks are sick of it.
On the other hand, when its basic needs of good soil and space to grow are met, honeylocust is a lovely tree that casts a light dappled shade and is tougher than nails, exhibiting few of those negative traits.
This medium-sized tree will grow 40-70 feet tall and 20-50 feet wide, depending on the cultivar. Most cultivars are developed from the variety ‘inermis’ which is (mostly) seedless and thornless, unlike the straight species with its dangerous triple-threat thorns and messy large bean-pods. ‘Shademaster’, ‘Skyline’ and ‘Streetkeeper’ are fine selections for locations that allow the tree to develop to its full potential.
The tree’s limbs are flexible yet strong, branching upwards and outwards from the trunk. Fine-textured twigs and leaves drape gracefully from the branches. Leaves are alternate and compound with half-inch leaflets. In early fall, the glossy green leaves turn a nearly flawless canary-yellow color before wafting off the tree. The tiny leaflets tend to disappear on their own with little mess.
Taken together, the branches, twigs and leaves compose a light, breezy canopy that is unique among shade trees. Light percolates through the crown, producing a sun-dappled shade that is aesthetically relaxing while allowing just enough light to keep turfgrass growing beneath.
The bark is attractively textured with long, gray plates separated by gray to gray-brown furrows for four-season interest.
No wonder it’s overplanted! Nonetheless I offer you this…
Let’s rethink the way we use honeylocust in the landscape. Forget the idea of honeylocust as a “tough tree”; it would actually like a little pampering to look and perform its best—the most extreme locations may not be the best locations for this tree to thrive.
According to the Morton Arboretum in Illinois, “… honey locust is overused in city and suburban landscapes. For the sake of species diversity, it should only be planted after careful consideration of alternatives.”
Honeylocust does best in full sun on moist, rich soils, although it can be equally successful on droughty sites with adequate irrigation. Remember that current research recommends a minimum of 400 cubic feet for healthy root development, and the beautiful full crown of the honeylocust requires space to spread out to its full shady glory.
So if you’re ready to revisit the honeylocust as an option for your landscape, make sure the planting location is optimally suited to the tree’s needs, and by all means, select a cultivar known to be fruitless and thornless.
Urban and community Forestry in Washington State 