There are two trees, hackberry (Celtis occidentalis) and sugarberry (Celtis laevigata), that produce the lumber known as hackberry. That is, in the trade that the names hackberry and sugarberry are used interchangeably. Sometimes the lumber from these species is called sugar hackberry. We will use the name hackberry here, but will be referring to both species. The species grows from North Dakota to Texas to North Caroline to Quebec, but the Southern states seem to have the best supply. Trees are often over 100 feet tall, although 75 feet is more common. The berries are edible, but because they are so high, the birds have their feast before they can be harvested.
Hackberry is a lumber species that does not stand on its own too often. Rather, it has been used as a substitute for red oak, ash or elm. Indeed, hackberry has strong grain and porous structure, so it is quite similar to these other three species.
Perhaps the greatest detriment to using hackberry is that it stains (fungal stains and chemical enzymatic oxidation gray stains) very quickly. Logs that have been held in warm weather or lumber that has not been promptly stacked and dried aggressively right after sawing will almost have high staining risk. Careless lumber producers will produce mostly “paint grade” hackberry because of the stain. However, with reasonable care, hackberry is a beautiful wood, worth of the high prices paid for the better grades or ash and elm.
Processing suggestions and characteristics
Density. Hackberry has a density of approximately 35 pounds per cubic foot (very close to cherry and American elm). Hackberry KD lumber weighs about 3 pounds per board foot at 7 percent MC.
Drying. Drying is certainly the one “problem” that we have with hackberry. The wood is very prone to staining if not handled and dried promptly, including prompt logging, sawing and stacking. In addition, using initial temperature in the kiln of 115F with very low initial humidities also helps to produce lighter colors, but such conditions do not cure any preexisting stain that arose due to poor handling. Note: A weak solution of oxalic acid (wood bleach) will remove most of the enzymatic stain on the surface of dry lumber or parts, rough or sanded. In fact, in the “olden days,” oxalic acid bleaching was frequently one essential step in the finishing system for hackberry.
Overall, hackberry shrinks slightly more than cherry, about the same as ash, and a little less than oak. Hackberry has 7% shrinkage from green to 6 percent MC, compared to 6 percent, 7 percent, and 8 percent for the other three species, respectively.
Gluing and Machining. Hackberry glues fairly easily. As with all species that have significant shrinkage, prompt gluing immediately (within an hour) after ripping is essential to avoid moisture changes in storage or during delays.
The wood machines easily. If over-dried, chipped grain may be encountered.
Stability. Hackberry does shrink and swell in use (when the humidity changes) a little more than some hardwood species, but not quite as much as oak or hard maple. Specifically, 1 percent size change in width (or tangentially) for flatsawn lumber for each 3.4 percent MC change and 1 percent thickness change (radially) for a 6 percent MC change. The grain is quite straight, so twisting does not occur and bow and side bend are rare.
Strength. Hackberry is a little stronger and stiffer than many other hardwood species; it is quite close to elm and just little below ash. The strength (MOR) at 12 percent MC is 11,500 psi, the stiffness (MOE) is 1.19 million psi, and the hardness is 880 pounds.
Color and Grain. This species is ring porous, so it has a region of large pores at the beginning of every ring, just like oak, ash, and elm. The sapwood is typically pale yellow. The heartwood, which often is not present, is yellowish gray or yellowish-brown. The wood can be finished naturally (I think it has excellent, attractive appearance when done “au natural.”) or it can be stained to closely resemble oak, ash and elm.
It certainly makes fine furniture and cabinets, but does not get as much use as “show wood” as I think it should. As the tv ad says: “Try it; you’ll like it!”