Hackberry Nerds Not in Lab Coats


Nowhere else on the planet will you find anything that compares to the geeky and up-to-date Garden Rant coverage of hackberries. Last week’s Guest Rant by Scott Beuerlein nudged the door on the belittled common hackberry. This week we will attempt to blow the door wide open with the dwarf hackberry. Does anyone care?

Seeds of the dwarf hackberry.
Seeds of the dwarf hackberry.

Never in my life did I imagine I would spend several days searching for hackberry seeds.

And then an email arrived last March.

Mike Hayman asked if I knew the dwarf hackberry, Celtis pumila (tenuifolia). He also wondered if I had any idea where he might find seeds.

I claimed ignorance, my occasional state of mind, but this was not numbskull stupidity. It was, instead, a shining awareness that there was much more to learn about a tree, growing nearby. I found this exciting in that way that Thoreau did when he wrote, “It is not what you look at that matters but what you see.”

David Fothergill, a Louisville native and landscape designer for the National Forest Service in Helena, Montana, had tipped off Hayman. Fothergill had seen Celtis pumila (tenuifolia) growing in the knobs of the Jefferson Memorial Forest, less than 20 miles from my Louisville home.

Celtis pumila, the dwarf hackberry.
Celtis pumila, the dwarf hackberry.

Celtis pumila was new to me. It’s a lower-growing hackberry, not at all rare in Kentucky, but one I had not noticed before. Hayman thought the dwarf hackberry might be a potential urban street tree.

Louisville is struggling with a diminishing tree canopy and holds the ignominious distinction of having one of the nation’s top five hottest urban heat islands. The city, alongside a variety of non-profits, is planting more trees to cool down the urban core. The tree lovers among us are hoping the mayor makes a bold and sustained public relations effort to promote the public-private initiative all across the city. His personal involvement, connecting the dots in Louisville neighborhoods, from Fairdale to Pleasure Ridge Park, Shively, Buechel, Smoketown, and down to Portland, is integral to whittling down the tree canopy deficit.

Mike Hayman, a retired Louisville Courier-Journal photographer, plants trees—lots of them.  He knows tree sources, makes contacts in neighborhoods scattered around the city, finds planting locations, secures funding and plants the trees. It’s a productive urban tree-planting model without the usual frustration of politics and a stifling bureaucracy.

Leaves of the common hackberry.
Leaves of the common hackberry.

I’ve got common hackberry seedlings (Celtis occidentalis) that seed bomb my garden every year. And there are a dozen or more volunteer hackberries growing along our back alley, within 50 yards of our garden. No one bothered to weed them out as seedlings, many years ago, or thought to cut them down once they took hold. So there’s been no love lost between us.

Hacberries have been the punch line of jokes in plant geek circles for years. Although many will admit that hackberries are hard to kill, rare is the gardener who courageously sings common hackberry’s praises. Scott Beuerlein is the rare exception.

Celtis occidentalis has anemic-looking green leaves that often become deformed with spindle galls. These leafy pimples never seem to cause serious damage, but they’ve caused the tree to be shunned as an ornamental. Still, all shades of green have a role to play in this story. And the distinguishing bark of the common hackberry can even be stunning.

Distinctive bark of the common hackberry.
Distinctive bark of the common hackberry.

Hackberries were once relatives of elm trees (Ulmaceae family) without the charm. Of course, the Dutch elm disease has decimated the American elm. No charm in that. Hackberries, however, are nearly indestructible.

The genus Celtis got shuffled to the (Cannabaceae family) a few years ago and now claims kinship with reefer. Don’t ask me how hackberry and marijuana rolled together. DNA diagnostics is lab coat science; I’m just a dirt gardener.

Even after forty years of close observation in nature, I freely admit: I don’t know diddly about dicots or hackberries.

Enter the skilled botanist Julian Campbell. He knows plenty about dicots (dicotyledons), our more evolved flowering plants, and hackberries.

Julian Campbell climbs the ladder for seed of the dwarf hackberry. Mike Hayman photo.
Julian Campbell climbs the ladder for seeds of the dwarf hackberry. Mike Hayman photo.

Julian is the one I contacted with Mike Hayman’s initial inquiry concerning the dwarf hackberry. He responded right away, saying he knew where some Celtis pumila were. Julian knows where many of Kentucky’s hidden treasures are. He plays at pro level in the plant world.

Last month Hayman reminded me that it was time to go looking for seeds. Julian Campbell led us to Franklin and Bullitt Counties, short distances from Louisville. Hayman even went to Adams County, Ohio, to collect with plantsman and amateur botanist Daniel Boone, a direct descendant of the famed Kentuckian. Trees were growing in poor, dry conditions that meant they might adapt to restricted urban conditions.

Daniel Boone collecting dwarf hackberry seed in Adams County, Ohio. Mike Hayman photo.
Daniel Boone collecting dwarf hackberry seeds in Adams County, Ohio. Mike Hayman photo.

Andrew Berry, Forester at Bernheim Arboretum and Research Forest, told me there was a naturally occurring bonsai of the dwarf hackberry on his farm in Mercer County.

But who cares?

The Beatles, Eleanor Rigby, kept banging around in my head, during the search for the lonely Celtis pumila.

All the lonely people

Where do they all come from?

All the lonely people

Where do they all belong?

Maybe David Fothergill, Mike Hayman, Julian Campbell, Daniel Boone and Andrew Berry will bring the dwarf hackberry out of the shadows.

Hayman sent six accessions of Celtis pumila seed to the Woody Warehouse in Indiana. The nursery is a good source of native tree species. They will sow the seeds. The projected timetable (from seed sowing to ready-to-plant one-inch trunk diameter in seven gallon grow bags) will take approximately three years.

Bark of dwarf hackberry. Mike Hayman photo.
Bark of dwarf hackberry. Mike Hayman photo.

It’s still little more than a fantasy but it’s exciting to imagine that one day the forlorn dwarf hackberry might find a home on city streets, hell strips, vacant lots and in Louisville’s parks.

There’s now a small fan club for the dwarf hackberry. Well, at least a half-dozen of us. There might be more to come.

An elated Julian Campbell said, “We’re all hackberry nerds, now.”


  1. Thanks you for this. There ARE hackberry nerds out there! I think this species may be present in the parks in New York City. It’s been driving me crazy because I’ve been seeing trees that are definitely hackberry but they are not Celtis occidentalis (we have those too). Often found on the rock outcropping in the parks in Manhattan, every part of the tree is smaller than common hackberry and the bark is smoother, not as warty. I’ve seen a few growing in better soil and all the features are still dwarfed, so it’s not just the tough growing environment, although it seems that is where they have found a niche. It looks like New York is out of the natural range of this species, so I wonder if this is a outlier of the population or it was introduced to the parks and has since naturalized. Both seem kind of suspect. It seems odd that they would bring such an obscure species to the parks of New York City. This species isn’t even listed in Dirr. This seems like the closest match I’ve yet to find.

    • The Hackberry drawf tree is adorable! I want one. But then again, I also want a miniature pig (have you seen those, they are native to the Bahamas….to die for.) I won’t ask my husband for both for Christmas. Now that is pushing it!! Might go for the pig then….just saying.

  2. Thank you. Please get nerdy on us whenever you like. I crave the more in depth look at the vast and complicated world of plants. There are enough places to get basic ho hum info.

  3. Excellent article, Allen. Having often been presented with conspicuous eye-rolling whenever I have mentioned the excellent attributes of our native hackberry to landscape-pro friends, I know where you’re coming from. For some reason, the numerous seedlings each year never have presented much of a problem here in the Carolina Lowcountry – at least, for me – and their ease of transplanting and readiness to grow have been attractions for me. Scott Beuerlein had mentioned, I think, the variety of wildlife which make wonderful use of so many parts of this tree.
    But for me, the great pleasure is the quality of the shade this deciduous tree provides during the growing season. The leaves are numerous, but light and small. Sunlight seems able to penetrate as a brightness below the tree, rather than the heavier shade offered by so many others of our trees. Our pines, when growing tall and limbed-up, provide a similar light shade. The pines, however, spread their roots at the surface, making the deep-rooted hackberry a much more desirable shade tree for planting many of our flowering shrubs beneath.
    I welcome, indeed, the Rant’s discovery and celebration of the hackberry!

  4. No hackberry fan here. Maybe there are too many in my garden; maybe they are too ugly, or maybe painfully plain is more accurate. But they are tough trees. Just wish two or three (all over 18″ in diam) could be given away.

  5. I must agree with Ryan. I’ve been wondering about the interesting plant in my side yard & you’ve identified it for me. I’m in NYC, too. My version is still fairly young, but thriving -1″ diameter at present. Is it possible my bird-feeding has brought it here?

    • M. Julian Campbell, our go-to Kentucky botanist, is doing a little bit of investigative work, with some of his NY colleagues, to try to figure-out if you and Ryan may have found the dwarf hackberry in NYC. Hopefully, more later.

  6. For a few seasons I hoped, idly, that the hackberry that sprang up at the back of a border might be the dwarf species. It’s right beside an old cement chicken coop foundation, and I feared the roots would speed up its destruction, but mainly I wasn’t sure the border could handle shade from a full-size tree. Now that the tree’s bigger, I see that I needn’t have worried about the shade, which is pretty minimal thanks to the small leaf size and the fairly compact canopy.

    This year the hackberry leaves actually turned a nice shade of acid yellow for a week before blowing off in three days of high wind. (Even the beech leaves are gone now; they usually hang on until after Thanksgiving. More light in the house, but less orange glow…)

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