Rinse sponges underneath hot water to remove food particles after dishes are finished, then wring them out as much as possible before storing. Relieving the sponges of water content will mean less standing water in the sponge container as the sponges dry. It also means the sponges will dry out faster, meaning less chance for mold, mildew and bacteria growth.
Use a shower soap rack to separate your kitchen sponges for drying. Dry one or two sponges in the rack at a time, and refrain from placing sponges on different tiers if applicable, as the sponges on the upper tier will drip down into the bottom tier and take longer to dry.
Place each sponge in a separate small plastic container. Use clean, dry containers, and wipe them out on a daily basis with a clean rag to keep them dry and to help prevent mold and bacteria from forming.
Separate the sponges in old metal napkin holders as an alternative to the plastic containers for drying purposes. Place one sponge each on its side in the holder slats for best results.
Spray the sponges a couple of times a week with white vinegar to help prevent bacteria and mildew growth. Replace sponges about every two to three weeks or whenever the sponges start to look gray or begin to fall apart.