Have a hard time remembering to water your houseplants? Here's a way to keep your plants alive and recycle old sponges all in one. When it's time to replace an old sponge, disinfect it by placing it in the microwave for about 90 seconds. Put the cooled sponge at the bottom of a planter. This will prevent soil from falling out, and it will also absorb excess water each time you water the plant. The wet sponge in the planter will slowly release needed moisture, helping to keep the plant alive in case you forget to water.