In a word, “NO”.  No truth in advertising…

new plastics are designed to degrade (not to be confused with biodegrade—more on that in a sec) in a matter of weeks when exposed to the elements, but that doesn’t mean they’re truly gone.

Can biodegradable plastics break down in landfills? This claim, which now shows up on everything from water bottles to trash bags to Discover’s “biodegradable PVC” credit cards, is “disingenuous at best,” says Narayan. Usually, nothing biodegrades in a landfill. But if biodegradable plastics do break down in this oxygen-free environment, they’ll emit methane, a greenhouse gas 23 times more potent than CO2.

http://www.motherjones.com/environment/2009/05/do-biodegradable-plastics-really-work