A Gardening Journal

Caspian Locust

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Green twigs in the Winter:  Always a good sight.  But that thorn!  Yes, it's one thorn; when you're a Caspian locust, even your thorns have thorns.  Green is good, but thorny is ferociously fantastic.  Caspian locust is the world champ of thorniness; its spikes are longer than those of any cactus.  And what other plant develops thorns that, themselves, have thorns that have yet more thorns?  

 

The tree's thorns-with-thorns-with-thorns give it a fractal ferocity.  My little sapling is just starting to feel its oats; on more mature trees, the thorns can be six inches long.  incredibly, they're not produced one by one, either.  They emerge by the fistful.  A dozen of these six-inchers in a cluster?  That's a fistful of thorns a foot across.  The clusters emerge directly from the trunk, as well as from branches and larger limbs.  If you have an unplanned encounter with a Caspian locust, that "fistful" would be literal.  Ouch.

 

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Can a plant be too thorny?  Maybe thorns are just another of its attributes, like showy foliage or flowers or bark or fruit, and worthy of the same intensity of appreciation, analysis, and celebration.  

 

And if that's the case, wouldn't eight-inch thorns be even better than six-inch thorns?  See "How to handle it: Another option—or two!" for one strategy to help Caspian locust produce thorns of maximum size.  And for suggestions on how this fierce tree can be incorporated safely into your garden.

 

 

Here's how to grow this dramatically dangerous tree:

 

Latin Name

Gleditsia caspica 

Common Name

Caspian Locust

Family

Fabaceae, the Bean family.

What kind of plant is it?

Deciduous tree.

Hardiness

Zones 6 - 9.

Habit

Single-trunked, upright, with broadly-spreading limbs.

Rate of Growth

Medium to fast. 

Size in ten years

Fifteen to twenty feet tall, nearly as wide.  Ultimately between thirty and forty feet tall, and twenty to forty feet wide. 

Texture

Medium; the compound leaves bring a lacy feel—but the astoundingly large and aggressive clusters of thorns brutally dispel all whiffs of softness. 

Grown for

the thorns, which are unique and unprecedented in any hardy tree.  Branched fistfuls of six-inch spikes erupt directly from the trunk as well as from major limbs and branches.  Was Sleeping Beauty snoozing in a forest of Caspian locust?  The jagged growth would repel any creature that wasn't driving a tank.    

Flowering season

Spring.  The flowers aren't showy.  They mature to bean-like pods, studded with seeds the size of lima beans. 

Color combinations

Caspian locust goes with everything.

Partner Plants

Caspian locust needs partner horticulture that helps protect visitors from unexpected encounters while it also enhances the tree's lacy foliage.  Large leaves would contrast beautifully; hostas would thrive in the tree's dappled shade, which is typical for all Gleditsia species and cultivars.

 

Dark green foliage can often be had with considerable shine, and both qualities would be shown off to advantage beneath the locust's mid-green compound leaves.  Cherry laurel thrives in shade, and its wide-spreading forms—'Otto Luyken' and especially 'Zabeliana'—are so broad as to be impenetrable.  Blue holly is hardier and more available in Zones 5 and 6.  Plant only females of these Ilex x meserveae hybrids directly under the tree; they are typically broader and more mounding than the males.  Site the necessary male within hailing distance but not within immediate view; its more upright habit and conspicuous lack of berries will be out of place.    

Where to use it in your garden

Caspian locust is a dangerous oddity, and should only be sited where there's no danger of injury.  But the bristling thorns are remarkable, even more so when studied up close; people will insist on gingerly finger-tipping the spikes.  See both "How to handle it" entries below for solutions.   

Culture

Full sun and any decent soil; good drainage is important.  The tree is tolerant but is native to a climate—central Asia, around the Caspian Sea—that can be dry.  Best, probably, is a hot and sparsely-rained Summer alternating with a wet, cool-to-cold Winter.  That said, my individual is establishing just fine in Rhode Island, which can be rainy in any season. 

How to handle it:  The Basics

Gleditsia caspica is easy to establish; it's keeping you and your garden visitors safe around it that's the challenge.  Yes, underplant trees with wide skirts of shrubbery or groundcover, but also plan for safe visits to the thorny trunk, which will happen no matter what you do.  If you grow the tree full-size—with a wide skirt of underplanting, still—consider putting in a line of stepping stones to within a couple of feet of the trunk.  Then people will know where to access the trunk.  The only thing worse than a harmless "Ouch" moment with a planned encounter with one thorn would be to have no easy access and so try to scramble through underplantings, then trip and fall into hundreds of thorns.

How to handle it: Another option—or two?

Gleditsia species and cultivars usually grow fast, and don't mind being pruned, either.  Indeed, they seem to grow all the faster because they've been pruned, with longer branches and, in cultivars with colorful foliage, deeper, more heat-tolerant, and longer-lasting hues.  If pruned—and ruthlessly—will G. caspica respond by growing even larger clusters of longer and more vicious thorns?

 

To find out, in the coming years I'll be training my Caspian locust into a pollard.  After the young plant is eight or ten feet tall, I'll lop off the top foot or two in late Winter.  I'll remove any lower branches, too, and also cut back the rest by half. 

 

After letting the tree grow on its own in Spring, Summer, and Fall, in late Winter I'll once again cut any vertical growth back to stubs.  But this time, instead of cutting side branches back by half, I'll cut the oldest side branches back to a couple of inches, as well as all the young stems that formed over the Summer.  That first round of pruning will have caused plenty of young branches to have emerged from the base of old branches, as well as directly from the trunk.  There's no need to retain the long shanks of the original branches that had been cut back only by half.

 

Pollarding also solves the problem of the older bark.  It's boring and brown, whereas younger bark is green.  Cutting off the old branches removes the old stems—and also encourages the growth of plenty of young green-barked ones.  How efficient.

 

A pollard of Caspian locust also has the practical benefit of limiting the size of the tree's canopy; perhaps concentrating is an even better descriptor.  And this makes it easier to site the tree closer in view with less danger that one of the bristling limbs of the canopy would be long enough to project dangerously overhead.  Even so, I'll cut off any branch that's growing too low.

 

But what about the thorns?  How will pollarding affect them?  Yes, they'll still have emerged on the trunk, which, remember, remains unpruned.  Those will be the "control" thorns.  What about on the thorns on the pollard's new branches?  Those will be the experimental thorns.  Will they differ from those on the trunk?  That, my friends, is the great unknown.

Quirks or special cases

None. 

Downsides

Besides the obvious danger of the incredible thorns, G. caspica is susceptible, as are all Gleditsia species and cultivars, to various pests and diseases.  Thornless Gleditsia (see "Variants" below) cultivars were planted by the millions, lining countless miles of streets and campus quadrangles—and so, of course, all kinds of diseases eventually caught up with them.  Plant Gleditsia sparingly; isolated individuals can live long lives below the radar of the bugs, bacteria, and fungal plagues that can demolish mass plantings. 

Variants

Gleditsia caspica not scary enough?  There's also G. horrida (now renamed G. japonica); it's similarly ferocious.  The only locust tree you'll encounter in normal usage is G. triacanthos var. inermis, which is completely tamed.  It's not only thornless, its flowers are a bit deformed, too, so it's virtually fruitless.  Gleditsia "fruit" are long twisted pods, like huge dried beans, and create huge litter.

 

I also grow—problem-free, so far—four cultivars of G. triacanthos: a low weeper, 'Ohio Prostrate'; a upright purple-leaved form, 'Rubylace', an upright weeper, 'Emerald Cascade'; and, at full and apparently irrepressible size, 'Sunburst'.

Availability

On-line, but only infrequently.

Propagation

By seed.

Native habitat

Gleditsia caspica is native to central Asia, in lands bordering the Caspian Sea. 

 
 
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