WOOD EXPLORER
by Gene Wengert
ewengert@wisc.edu
Hackberry
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
The poor
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. ❮
man’s oak, ash
or elm?
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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.
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.
Processing suggestions and characteristics
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.
Gluing and Machining. Hackberry
glues fairly easily.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 humid-
ity changes) a little more than some
hardwood species, but not quite as
much as oak or hard maple. Specifi-
cally, 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. 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, just like oak, ash, and
elm. Sapwood is typically pale yellow. 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.
