Almost all potting soils include two or more ingredients such as peat to hold water, perlite to give aeration, and bark or vermiculite to hold nutrients. These should be thoroughly and uniformly mixed for good root growth. It is quite common for soil mixes to slowly “shrink” over time, due to decomposition of organic components as well as settling. The net result is typically an increase in water holding, with a decrease in aeration (usually referred to as “souring”). Mixing in new medium periodically will freshen the pot. To do this, gently remove the entire plant, add new soil at the bottom, rough up the sides and top of the original root ball, then replace your plant, firming new soil onto surface. Normal garden soils are not recommended for indoor plants. Besides questionable water and nutrient-holding characteristics in containers, they may contain insect eggs, weed seeds and disease organisms.