PLA is the most common filament for home printing, and it's often called "biodegradable." A year-long experiment covered by Hackaday shows what that does and doesn't mean.
The maker behind the YouTube channel "I built a thing" buried PLA samples in garden soil and in compost through a winter and a hot, dry summer. When they were dug up, they looked about the same as samples that had stayed indoors, and a strength test found no statistically significant difference. A lab test at the University of Basel found the PLA gave soil microbes nothing to feed on.
The maker also contacted commercial composting facilities in Switzerland, Germany and the USA. Many accept PLA in general, but none would take 3D printed PLA parts, mainly because they break down too slowly to be worth it.
What this means at home: PLA is still a great, easy material for kids' projects, but it isn't backyard compost. Keep failed prints out of the garden, reuse them for test pieces and crafts, and save filament by previewing each model in the slicer before you press print.
Source: Hackaday: “Disposing of PLA and Why Composting is Not an Option” (Oct 16, 2026)