Modern-day sponges are made mostly from petroleum and are neither recyclable nor biodegradable. But if you look more closely at labels the next time you shop, you can find sponges that are made from 100 percent cellulose. Made entirely from wood fibers, cellulose sponges have the look and feel of traditional sponges, but unlike petroleum-based ones, cellulose scrubbers can be tossed into the compost bin when it's time to replace them. You can even cut them into squares and mix them with soil for houseplants. They'll absorb water and slowly release it back to the plant over time.