Everything falls apart, even mattresses. Springs will lose their springiness. Stuffing will get knocked out. Grape juice stains might come into play. Adjustable beds will become less so. This is old-fashioned mattress-style entropy.
According to a chiropractic website, a mattress should last about ten years. That's the same lifespan as a pet rabbit. You can buy a rabbit and a mattress at the same time and when the rabbit dies, you'll know that it is time for a new mattress.
The rabbit can be turned into a rich stew. But what do you do with your old mattress? Many landfills are charging high fees for allowing someone to drop off their mattress or they are denying entrance all together. Those landfill people are sure getting snooty.
Most home-furnishing stores or mattress outlets will take your discarded bed parts, though there is no guarantee that you local furniture store won't just ship it all off to a landfill, so ask around before you donate. You should also find out if any bed retailers are recycling mattresses, because, although rare, mattress and box spring recycling does exist.
A well-oiled recycling factory can reuse 90% of the mattress. The cotton and cloth get turned into clothes. The springs and the foam get recycled, and the wood gets turned into chips.
In some areas, you can also refurbish your mattress and donate it to charity. (In other regions, it's not allowed. You can find out more about the rules in your local area at MattressDonation.com.) Still, some box springs and mattresses will be too far gone to refurbish and will have to be recycled