WoodSense: Spotlight on Catalpa

Catalpa Quick Take

This ornamental tree is a woodworker’s delight.

If you were to spy a rough-sawn catalpa board, you might mistake it for ash or even oak—it looks quite similar to these more familiar species. But once you picked the board up you’d realize the wood is significantly lighter in weight than ash and much lighter than oak.

Nearly the entire trunk of a catalpa tree is composed of heartwood that ranges in color from tan to golden brown. The growth rings tend to be a bit wider than ash or oak, and they are quite prominent due to lots of contrast between the wider pores of the earlywood and the latewood’s smaller pores. When filled with finish, the earlywood pores can take on an almost iridescent shimmer.

Where catalpa comes from

Unfortunately, catalpa isn’t grown commercially for lumber. This is probably because the trees tend to branch out quickly, usually just 4 ft. or so from the ground, so a tree won’t produce a lot of usable lumber. However, catalpa has a history as a popular ornamental tree due to its broad leaves and showy white flowers (see photo, opposite). Two species of catalpa are native to the eastern United States—Catalpa bignoniodes (southern catalpa) and Catalpa speciosa (northern catalpa). Both species have been planted ornamentally all over the United States. The southern catalpa is smaller and is the preferred ornamental tree because it tends to produce more blossoms. The northern variety can grow up to 100 feet tall and 2-4 feet in diameter.

So, while you won’t typically find catalpa at your local lumberyard, savvy local sawyers will often harvest trees that become available to them. Search online and you’ll find catalpa for sale in sizes ranging from small turning blanks to wide planks. The working characteristics and appearance of both species of catalpa are very similar and sellers usually don’t specify which you are getting. Of course if you find wide planks, they are probably northern.

History in woodworking

With the expansion of railroads in the 1870s, large tracts of Catalpa speciosa were planted with the intention of producing railroad ties. The hopes were pinned on the fact that the trees are fast growing and rot resistant. Also, unlike harder species such as oak, it’s easy to drive spikes into catalpa timbers. However, it soon became evident that the wood was too weak to support rail traffic. Most of these trees were planted on large tracts of mid-western prairie land owned by railroad companies. Much of this lumber found use as posts to support barbed-wire fencing.

In the late 1800s, catalpa became very popular as an ornamental tree and it was during this period that many trees were planted all around the country. While catalpa trees are no longer as popular as they were during that 19th century fad, they have self-propagated extensively, which is why the wood is now available to those willing to seek it out.

How to select the best stock

Because there is no organized retail market for catalpa, prices can vary greatly. A recent online check found prices ranging from $2.50 to $12.40 per board foot. The problem with buying online is that unless the buyer posts good pictures of the specific boards you will get, or is willing to send you photos, you won’t know the quality of the stock you are purchasing. To make matters worse, there is no standard grading system for catalpa. On a positive note, because of its stability, catalpa doesn’t usually twist or check, so your chances of receiving stable stock are pretty good.

If you’d like the opportunity to select your boards and you are not in a hurry, call some local sawmills and ask them to let you know if a log or two comes their way.

Some of the most interesting and shimmery grain forms around knots, so you might find tight knots to be desirable. However the wood around knots tends to be brittle and can chip out, leaving divots that you may need to fill because they are too deep to sand away.

Working catalpa in the shop

Catalpa is very easy to work with both power tools and hand tools—shavings whisk off a sharp hand plane with little effort. It carves easily and holds a crisp edge. Turners often seek out catalpa because it is so easily worked. They also like the interesting patterns produced by catalpa’s bold grain.

Once dried, catalpa is a dimensionally stable wood—a nice feature if you want your turned bowl to stay round. It’s also rot resistant, even in ground contact. These qualities put catalpa alongside cedar and cypress—excellent choices if you want to make durable outdoor furniture.

Finishing catalpa

Catalpa can be tricky to finish, mainly because the fine-pored latewood absorbs much less finish than the large-pored earlywood. When spread across the surface of a board, this uneven absorption will create a blotchy appearance. You can avoid this by conditioning the wood—with a wood conditioner or by applying several light coats of shellac. Follow this treatment with several coats of oil finish and you’ll have the best way to bring out catalpa’s natural shimmer and orange/yellow tone. Staining catalpa isn’t recommended because it usually results in a muddy appearance. If you must stain, stick with a light application after conditioning the wood surface as described above (see photo, top right).