Hey Mr. Green! Recycling plastic is good for the environment and the pocketbook, but what about compostable plastic products meant to be thrown away instead of recycled? I'd hate to find out that my Trex recycled plastic decking is made from compostable plastic.

—Brian in Oakland, California

Compostable plastic is not as virtuous as it sounds, because it doesn’t biodegrade very fast unless it’s exposed to ultraviolet light or hits a temperature of 122 degrees Fahrenheit. Such conditions exist in large municipal composting facilities but most likely not in your backyard heap or outdoors or in the ocean, says a study sponsored by the United Nations.

It’s always a bad idea to mix biodegradable plastic in a recycling bin with ordinary plastics, because if biodegradable plastic gets mixed with conventional plastic it can weaken the product. Trex informs me that the company does sort out all alien, unacceptable plastic for its boards, including biodegradable plastic, so your deck should be safe.