Black locust is excellent firewood and one of the hottest-burning hardwoods commonly available in North America. It produces roughly 28 million BTUs per dry cord, burns for a long time, and leaves an excellent bed of coals. Properly seasoned black locust also produces relatively little smoke and few sparks.
There are trade-offs. The dense wood can be difficult to split, takes time to season, and may be slow to ignite in a cold stove. Once burning well, however, it provides considerably more heat per cord than red oak, ash, or cherry. For serious winter heating, black locust belongs near the top of the list.
Black Locust Firewood at a Glance
| Heat output | About 27.9 million BTUs per dry cord |
| Dry weight | About 4,016 lb per cord |
| Overall quality | Excellent |
| Ease of splitting | Difficult, especially when knotty or twisted |
| Smoke | Low when properly seasoned |
| Sparks | Few |
| Coals | Excellent and long-lasting |
| Fragrance | Slight |
| Seasoning time | Allow at least 12 months; large splits may need longer |
| Target moisture | Below 20 percent |
| Main drawback | Hard work to process and slower to ignite |
How Much Heat Does Black Locust Produce?
Utah State University Extension lists black locust at approximately 27.9 million BTUs per dry cord. Its firewood table gives it a dry weight of 4,016 pounds per cord—an indication of just how much dense wood is packed into the same 128-cubic-foot volume.
Published figures vary. Oklahoma State University Extension gives black locust a recoverable heat range of 23.2 to 28.3 million BTUs per cord. Moisture, density, calculation method, and the amount of solid wood in a cord all affect the result.
Using Utah State’s figures, black locust provides more heat per cord than red oak at 24.6 million BTUs, honey locust at 26.7 million, and cherry at 20.4 million. It falls just below white oak at 29.1 million and well below Osage orange at 32.9 million.
Black locust performs so well per cord because it is unusually dense. A stove-sized split contains more wood—and therefore more stored energy—than the same-sized piece of a lighter species.
How Black Locust Firewood Burns
Dry black locust produces strong, steady heat rather than a quick flash. Utah State rates it as low-smoke, low-sparking firewood with excellent coals. Those coals continue releasing heat after the visible flames subside, help carry a fire overnight, and make the next load easier to ignite.
Its density can make black locust reluctant to catch from a weak flame. Start with plenty of dry kindling or a more easily ignited wood, establish a hot coal bed, and then add the locust. Small splits are useful during startup; save the larger pieces for after the stove is operating properly.
A full firebox of black locust contains a large amount of energy. Avoid packing the stove merely to achieve the longest possible burn. Use sensible loads, maintain adequate airflow, watch the stove or flue thermometer, and follow the appliance manufacturer’s operating limits. It may be more heat than needed during fall and spring.
Black locust has only a slight fragrance. It can work in an open fireplace because it throws few sparks when dry, although a screen is still essential. Its greatest value is in an enclosed stove where its long burn and coal production can be put to work.
The Main Drawback: Difficult Splitting
Utah State’s firewood table rates black locust as difficult to split. Straight, smaller rounds can open cleanly, but large trunks, forks, knots, twisted grain, and old pieces may defeat an axe or maul.
Split it as soon as practical instead of leaving full rounds to dry slowly. A sharp maul may handle clean sections, while wedges or a hydraulic splitter are more realistic for large and branchy wood. Smaller splits dry faster and make the dense wood easier to ignite.
Watch for sharp thorns on young branches, shoots, and root suckers. Wear gloves and eye protection when processing the brush. Older trunks may have few visible thorns, but thorny growth can surround the tree.
How Long Does Black Locust Take to Season?
Give black locust at least one full year after splitting and stacking. Twelve to 18 months is a sensible working range, while thick pieces in a damp or shaded location may need two summers. A calendar alone cannot confirm that firewood is ready.
The US Environmental Protection Agency recommends storing hardwood for at least a year and burning it below 20 percent moisture. Check black locust with a moisture meter on the newly exposed center of a freshly split piece. The weathered outside can appear dry while moisture remains inside.
Stack it off the soil, cover the top, and leave the sides open to airflow. Black locust heartwood is exceptionally decay-resistant, but that does not replace proper firewood storage.
How to Identify Black Locust
Black locust (Robinia pseudoacacia) is native mainly to the Appalachian Mountains and parts of the Ozarks, but it has naturalized widely. It grows rapidly in disturbed ground and can form colonies through root suckers. Some states consider it invasive or regulate it as a noxious weed.
University of Minnesota Extension and Iowa State University describe these useful identification features:
- Bark: Mature bark is dark gray-brown and deeply furrowed, with interlacing or flat-topped ridges.
- Leaves: Alternate and pinnately compound, usually with 7 to 21 oval leaflets. The leaflet edges are smooth rather than toothed.
- Thorns: Young twigs and vigorous shoots carry pairs of short spines at the base of the leaves, commonly around half an inch long but sometimes longer.
- Flowers: Fragrant white, pea-like flowers hang in showy clusters during late spring or early summer.
- Seed pods: Flat, smooth brown pods approximately 2 to 4 inches long, often remaining on the tree into winter.
- Growth habit: Root suckers frequently form tight groves or thickets around established trees.
- Wood: Narrow pale sapwood surrounds yellow-green to golden-brown heartwood that darkens with age.
Black Locust vs. Honey Locust
Despite the names, black locust and honey locust are different species. Black locust usually has short paired spines, smooth-edged oval leaflets, white hanging flowers, and short flat pods. Wild honey locust may have huge branched thorns on the trunk and limbs, smaller leaflets, and much longer pods. Thornless landscape varieties make thorns an unreliable feature, so compare several characteristics.
Is Black Locust Worth Burning?
Yes. Properly seasoned black locust is among the best firewoods for home heating. It combines very high heat per cord with a long burn, excellent coals, little smoke, and few sparks. It is especially valuable for overnight stove loads and the coldest part of winter.
The downside is the processing. Black locust can be hard to split, needs at least a year to season, and benefits from good kindling during startup. Straight logs may also be valuable as naturally durable posts or specialty lumber, so consider saving the best material and burning the lower-grade pieces.
If you already have access to black locust and can process it safely, it is absolutely worth adding to the firewood stack. Mix it with easier-lighting wood when starting a fire, use moderate loads, and let its dense coals do the heating.
So, I’m learning here in VT. We have a bad neighbor who wouldn’t cut down his huge spindly Black Locust trees that were wind-blown and leaning so much that they were threatening to fall on our house. We called a tree company to come and cut 3 of them – with the neighbor’s permission – and we got charged what to us was a fortune for the work. Still, we’re retired, I’m physically fit, have good saws & the right tools, so it made some sense to me to do this as we heat with wood. I figured we’d break even and not have to buy wood this year. We asked the tree company to cut limbs and pile them and stack the massive trunks in another area. They sat for 3 years to season. I tried bucking them while green and gave up after cutting a few rounds. I found it impossible to split the green rounds with ax, maul, and wedge and sledge. Even after 2 years out the maul would just bounce off the rounds, and it just wasn’t possible to get the wedge started. And I kept reading how great black Locust was. You can’t burn logs the size of your stove. I felt that I had made a really big mistake. Last year I bought an electric 1 ton splitter from Harbor Freight, and I wasn’t surprised that it wouldn’t do squat. I had to try it because, well, I’m a guy. My plan was to split the rounds into at least quarters and hit those with the splitter. But I had to split them first. Tried again this summer. Rubber. I gave it another shot this past fall, and finally – FINALLY – I was able to pop the rounds into quarters. I’m sure a bigger splitter would more adequately do the job earlier in the drying cycle, but I can’t afford one. My little electric splitter actually did a respectable job once I was able to split the rounds down, and I split them down into what I would burn – really small thicknesses. Smaller than what you would normally split Maple or Ash. After stacking in the woodshed we had 4 cords out of 3 trees. I found that the Locust was tough to get lit until I realized that it needs to get really hot to get burning. I split a bunch down to kindling size with a big batton for kindling, and used one piece of fatwood to get things going. I habitually split my fatwood with a small batton- the kind that comes in a bag – because it’s less wasteful. So, it’s December, and we’ve been burning just Black Locust. The flame is nothing like other woods, and the wood burns hotter than anything I’ve ever used. If the wood flamed in our stove like other woods there is no way we could handle the heat. This burns H O T. It burns more like coal and less like wood. The coals are wicked, wicked hot, and easily catches new logs when you feed it. The stack temperature is no where near what I’m used to, so I worried about creosote, but then, it’s burning so freaking hot, and so complete, and it’s by nature so low in sap and resin that perhaps there is none. It leaves hardly any ash, and zero carbon chunks. None. Remarkable stuff. Worth the work.