Honeylocust provides abundant shade, grows quickly and adapts well to extreme conditions

Acer (maple) and Quercus (oak) may monopolize spotlights on shade trees, but Gleditsia triacanthos var. inermis (honeylocust) holds its own as a major crop and it’s an important addition to the catalog of reliable tall trees.

Oregon nurseries grow more honeylocust than any other state in the U.S., providing 20% of the trees grown in the country — about $2.6 million in sales annually, according to the USDA.

Although it was overplanted in the 1980s and 1990s (leading to certain issues with pests and diseases for some urban forest monocultures), honeylocust makes a contribution today to maintaining a diverse mix of trees. It is still recognized by experts as a reliable performer, and has a dependable selection of varieties, including a new introduction by J. Frank Schmidt & Son Co. (Boring, Oregon) after years of trialing.

Attractive attributes

Overall, demand for honeylocust remains stable, consistent and strong, according to Rich Bailey, national sales manager of Schmidt. He views the Midwest as a hotspot for sales because of the tree’s hardiness and adaptability. It has an ability to tolerate extreme cold and heat as well as highly acidic to highly alkaline situations.

“Honeylocust is a reliable plant that can tolerate a wide range of soil and moisture conditions,” said Marion Hageman of Robinson Nursery Inc. (Amity, Oregon). It thrives in drought and wet, plus it withstands pollution. It’s a popular choice in urban settings nationwide and in landscapes meant for fast-growing, larger trees. Honeylocust ranges from 35 to 70 feet tall and 20 to 50 feet wide.

“It is not a tree where you are going to find 20 in a yard,” said Tim Sester of Sester Farms Inc. (Gresham, Oregon). “You’re going to put one here and one there. They’re big. I’ve seen honeylocust used along driveways, and they have a lot of neat characteristics.”

They have a unique scent. “It’s kind of like the name; it’s sweet,” Sester said.

“Pretty much every area [of the U.S.] likes honeylocust,” said Tom Epler of EF Nursery Inc. (Forest Grove, Oregon). The grower sells honeylocust to markets from Denver westward. “In Denver, I’ve seen it in parking lots, and in Utah, it’s a good parking lot tree too.” With its large stature, honeylocust “covers an area to produce shade, keeping cars and parking lots cooler.”

Sales are strong for honeylocust, said Sester, because it provides an alternative to maple. “Sprinkle in some honeylocust, even where there is higher alkaline ground, and they do just great,” he said.

“[At maturity], it is light and airy,” Epler said. “Great for parks and for streets, if you have the room.”

There are pluses and minuses with the great number of small leaves. They potentially can clog gutters if planted too close to the house, but the leaves, which turn yellow in fall before dropping, are of such fine texture, they almost evaporate in lawns and parking strips, requiring little raking.

Honeylocust has a place in large landscape projects — at least 15 feet away from structures, 3 feet from fencing or pavement and 25 feet from overhead electric wires for tall trees, according to the USDA Forest Service “Tree Owner’s Manual.”

For the most part, Hageman said honeylocust is used in commercial and highway projects, in parks and as street trees by municipalities. It’s rarer to be placed by homeowners. “[It’s] a showy flower, and the fall color is yellow, rather than the preferred reds, oranges and purples,” he said.

Production challenges

One of the main challenges of growing honeylocust successfully is pod gall midge (Dasineura gleditchiae), which feeds on emerging leaves in spring. Bailey explained that the presence of this insect can affect the aesthetic of the tree by destroying new growth and distorting the central leader and branches. Although the midge can be hard to detect, a combination of diligent field scouting and the application of appropriate sprays when needed keeps the trees clean, he said.

“Any nursery of any size on a spray program, they understand pod gall midge; it’s manageable,” Sester said.

All selections of honeylocust require frequent pruning in the first few years at the nursery to develop the branching structure the market desires, Hageman said.

“Timely, specific pruning practices ensure that sunlight will reach the lower branches for better limb formation and overall canopy structure — factors that aid in survivability,” Bailey said.

Epler adds that honeylocust requires a little more lime than other trees to grow to gets to the size for sale. “It will just take off, unless they have too alkaline or too acidic soil.”

To get a saleable tree with a 2-inch caliper takes about four years. Although the market is not there for very large sizes, Epler sells large trees ball and burlap, which can be a challenge. You must tie them just tight enough before they crack. It’s a balancing act. Tie the tarp too tight, and the branches will break.

“But for the most part, they transplant well with limited losses if dug at the proper times of year,” Hageman said. “Due to their rapid rate of growth, honeylocust can quickly become an attractive addition to the landscape.”

Dependable varieties

Honeylocust cultivars are marked mostly by subtle distinctions. Skyline^® honeylocust (Gleditsia triacanthos var. inermis ‘Skycole’; Zone 4, 40–45 feet high by 25–35 feet wide) receives top billing as the most popular, and all growers interviewed here produce it.

“It is what I refer to as ‘grower friendly,’ meaning a central leader can be established and maintained,” Hageman said. “It has a strong rate of growth, and can obtain marketable sizes in a reasonable number of growing seasons.”

“Skyline has a very nice texture, with golden fall color and a pyramidal shape,” Bailey said. “It is the most widely used, and a nice tree for its environmental tolerance, which is important.”

This variety has stood the test of time, having received its patent in 1957. Like all varieties listed here it is “inermis,” Latin for “unarmed,” for the spines that have been selected out (although some mainstream sources still are unaware), and in most cases the seedpods as well. Skyline is more uniform than the next most asked-for, and grown, variety, Shademaster^® honeylocust (Gleditsia triacanthos var. inermis ‘Shademaster’; Zone 4; 45 feet high by 25–35 feet wide).

‘Shademaster’ has a more open form than Skyline, producing an upright vase shape with irregular, different branching, which landscape architects seem to like and ask for specifically. Epler started growing Skyline because of demand.

‘Shademaster’ has a vase shape that may not be as strongly upright as Street Keeper^® (Gleditsia triacanthos ‘Draves’, PP 21698; Zone 4; 45 feet high by 20 feet wide) or Northern Acclaim^® (Gleditsia triacanthos var. inermis ‘Harve’; Zone 3b–6; 35–45 feet high by 30–35 feet wide), but it’s good for traffic clearance because it can be pruned up high, according to Bailey .

Street Keeper, developed by Schmidt, was discovered in a residential area of Darian, New York, and observed for more than 20 years before being introduced commercially. It has become a desired street tree for its strongly upright, tight and columnar habit, and was bestowed Best Tree of the New Varieties Showcase at the Farwest show in 2011. It has a darker green leaf than other varieties and a good central leader, and is usually seedless.

There may be subtle differences between Northern Acclaim and other honeylocust, but it being a zone hardier makes it a tree in demand, Sester said. Selected by Dale Herman at North Dakota State University, it has an upright shape similar to Skyline that gradually widens with age.

For a smaller, more compact variety, Imperial^® honeylocust (Gleditsia triacanthos var. inermis ‘Impcole’; Zone; 30–35 high by 30–35 wide) has a rounded crown, slower growth and denser branching that helps to resist storm damage, according to Bailey.Epler considers it a good tree for eastern Oregon and areas like it because it thrives in dryer, warmer climates. And Sester said it is slower growing.

Introductions of honeylocust are less common than other shade tree varieties. Honeylocust started getting serious attention from growers in the 1990s, when demand started to increase, and like Epler and Sester, growers often started with two or three varieties to begin, and have since expanded. Schmidt offers seven cultivars of honeylocust.

“Over the last 20 years, we’ve only added three cultivars to the catalog, with our last introduction made in 1999,” Bailey said.

That was Halka^™ honeylocust (Gleditsia triacanthos var. inermis ‘Christie’; Zone 4, 40 feet high by 40 feet wide). Halka is notable for a rounded, symmetrical form and little branch drop. Its fast-growing trunk in early development results in a strong, heavy caliper at a young age. Then came Northern Acclaim in 2005, valued for its extreme hardiness, and Street Keeper in 2010, notable for its smaller and narrower stature.

Eleven years later, the 2020–2021 catalog debuts Northern Sentinel^™ honeylocust (Gleditsia triacanthos ‘JFS GMorgenson1’; Zone 4; 45 feet high by 25 feet wide). It joins the Sentinel^® family of upright, narrow or compact trees ideal for city streets.

The initial offering of whips ranging in size from 5 feet to 8 feet were quickly reserved by existing customers. The nursery is building its inventory and anticipates having a larger number of whips plus branched trees of various sizes available in 2021–2022.

Discovered by Greg Morgenson, a research specialist in the North Dakota State University Plant Sciences Department, this unusually narrow and upright tree has been observed by Morgenson for years. Entrusted to Schmidt for co-introduction, Northern Sentinel was trialed at the nursery for seven years before it was deemed ready for introduction.

“We don’t introduce a new tree that isn’t better or an improvement over other trees already available in the marketplace,” Bailey said. “The key advantages of Northern Sentinel are its unusual form and excellent hardiness. It’s very adaptable, and can take harsh environments, from extreme heat to extreme cold.”

Thanks to its narrow, upright growth habit, Northern Sentinel is storm resistant, with no observed snow, wind or ice damage to the parent tree over a period of many years. Nor has the parent been observed to produce seed, a feature that can be influenced by environmental factors, but a promising sign that its offspring may also be seedless.

“It’s a great addition to the Honeylocust cultivars, and a great fit for street tree plantings where branches must be pruned up for traffic clearance,” Bailey said.

For now, honeylocust is a tree in demand. Although sometimes it is hard to appreciate honeylocust as a small sapling growing in the nursery, it pays off in the end.

“When you see it as a big tree, that’s where it really shines,” Sester said

And with its ability to survive drought and extreme weather conditions, the need for honeylocust is expected to stay consistent as landscape projects continue to look to maintain diversity and to spec tough trees.

Tracy Ilene Miller is a freelance writer and editor who covers several topics,
including gardening. She can be reached at [email protected].