Catalpa — Density, Movement, Workability & Cost

Catalpa (Catalpa speciosa) has one of the lowest volumetric shrinkage figures of any hardwood the USDA Forest Products Laboratory has tested — lower than every domestic species on this site — and it earned that stability rating while also being soft enough to carve with a dull knife. Those two properties don't usually travel together, which is exactly why nineteenth-century farmers planted entire catalpa groves purely to grow their own fence posts.

Startling stability from an unremarkable-looking tree

At 29 lb/ft³ and 550 lbf on the Janka scale, catalpa is light and soft — it cuts as easily as a coarse ash and holds no particular hardness advantage over any competing softwood. What sets it apart is a volumetric shrinkage of just 7.3%, remarkably low for any hardwood in the FPL's tables, meaning a catalpa post or board holds its shape through humidity swings that would visibly move a denser, seemingly "tougher" species.

The numbers behind why it barely moves at all

Radial shrinkage of 2.5% against a tangential figure of 4.9% gives a 2.0 ratio — technically at this site's movement-prone threshold, but with both raw numbers so low that the practical effect is minimal. A 10"-wide board, seasoned outdoors from a wet 14% down to a drier 8%, loses less than a tenth of an inch, 0.098" (2.5mm), across its width; other widths and swings run through the wood movement calculator. A 1"-thick, 6"-wide, 8-foot fence board weighs about 9.7 lb; other board sizes run through the wood weight calculator.

Easy to cut, easy to glue, hard to find in quantity

Catalpa bonds cleanly under ordinary PVA glue, with nothing about its open pore structure causing any particular difficulty. Indoors, a clear finish preserves its natural greyish-brown tone; left outdoors and unfinished, it weathers to a silver grey the way many stable, moderately durable woods do. The practical limiting factor is supply: catalpa is nearly always an ornamental tree removal rather than a managed timber crop, so boards tend to be short.

Durability, cost, and its historical farm-fence role

Catalpa's heartwood is durable, unusually so for a wood this light — the combination of decay resistance and low movement is exactly what made it worth planting deliberately for fence posts a century ago, when a farmer needed a post that would hold its shape and resist rot without buying imported or treated lumber. At roughly $7 per board foot it's priced in this site's moderate tier despite the modest commercial demand. Fence posts, outdoor furniture, carving, picture frames, and utility poles round out its uses.

An overlooked option worth considering

Against black locust, the other domestic species prized for post-and-fence durability, catalpa gives up real density and hardness but matches it on dimensional stability while being considerably easier to carve or shape by hand — a genuinely useful tradeoff for a project that values ease of working over maximum toughness.

What people actually ask about catalpa

Is catalpa lumber commercially available, or do I need to find my own tree? Commercial supply is limited and regional; most catalpa reaching a woodworker comes from a removed ornamental tree rather than a lumberyard order, so sourcing usually means networking with local tree services or sawyers rather than a standard supplier.

Are catalpa fence-post groves still actively maintained anywhere today, or is that entirely a historical practice? It's almost entirely historical at commercial scale — pressure-treated lumber removed the economic case for dedicated post groves generations ago, though scattered old catalpa plantings from that era still stand on farms across the Midwest, occasionally harvested by a landowner who inherited the trees rather than replanted them on purpose.

Is catalpa strong enough for furniture, given how soft it is? It's adequate for lightly loaded furniture and casework but dents easily under point pressure; its real advantages are stability and workability rather than hardness, so it suits carved or decorative pieces better than anything meant to take heavy daily wear.

Catalpa doesn't appear in the USDA Forest Products Laboratory's main species tables, so density, Janka hardness and shrinkage here are all The Wood Database's figures, which cite that same federal handbook for methodology.