Is “biodegradable” the same as “compostable”?

No. “Biodegradable” means that something will eventually break down into its biological elements given the right conditions, including the presence of microorganisms, fungi, or bacteria, light, and oxygen. The name implies that these materials would break down without leaving any chemicals behind, but that is not always the case, even for items with a biodegradable label. Certain biodegradable plastics, for example, are made of the same petrochemicals that traditional plastics are, but they are also composed of other chemicals that speed up the decomposition process. When they break down, they leave the traces of their source materials. “Compostable” refers to a subset of biodegradable items that can break down quickly (less than 180 days) into a nutrient-rich soil, again in the right setting. Most compostable packaging and tablewear items require a composting facility to break down properly (your backyard compost heap won’t cut it). They need the controlled environment and high temperatures of the facility to break down into humus (that gardener’s “black gold”).