can you compost treated wood?
No — pressure-treated lumber is infused with copper compounds, and pre-2004 stock with arsenic; the preservatives leach into compost and soil.
which bins can take it?
- hot pile no
- cold pile no
- worm bin no
- bokashi no
- tumbler no
- curbside no
- curbside: Yard-waste programs exclude construction lumber — treated wood contaminates their finished compost.
why?
Pressure treatment forces preservatives deep into the wood — chromated copper arsenate in residential lumber sold before 2004, copper-based formulas like ACQ since — specifically to stop fungi and bacteria from digesting it. A pile can't break down wood engineered to resist decay, and as the surface weathers it sheds copper and arsenic that persist in finished compost and can be taken up by root crops.
watch out for
- Never burn treated wood — smoke and ash concentrate the preservatives, and open burning of it is banned in many states.
- Sawdust from cutting treated boards is just as contaminated as the lumber — bag it for the trash, and keep it off garden paths.
what to do instead
Take treated lumber to a construction-and-demolition landfill or your county's bulky-waste drop-off. Sound boards can be reused for non-garden projects, but keep old CCA-era wood away from anything that grows food.
often confused with
- Untreated Wood — Raw, unpreserved lumber is plain carbon — slow to break down, but a legitimate compost material once chipped or shredded.
quick answers
How do I tell if old lumber is pressure-treated?
Look for a greenish or brown tint, rows of small incision slits, and an end tag stamped ACQ, CA, or CCA. Weathered gray boards hide the color, so when the history is unknown, treat the wood as treated.
Is newer treated wood safer than the old green stuff?
Safer to handle, yes — the arsenic is gone. But ACQ and copper-azole boards are loaded with several times more copper than CCA ever was, which is why they eat through ungalvanized fasteners. That same copper is a broad-spectrum fungicide, so the board still refuses to rot and still sheds a microbe-killing metal.