Indoor heat from radiators and even air conditioning can dry your plants out quickly. To prevent this mix equal parts of potting soil with non-clumping kitty litter. The kitty litter will hold the water better than the soil while it slowly provides hydration. If your home is particularly dry, place you plants on a shallow saucer or tray filled with pebbles and a little water. As the water evaporates it will boost humidity to your plant to keep it hydrated.