Most house plants need repotting every year in our area. Our alkaline water contains high levels of salts that build up quickly in potting soils and barks. Within a year or so, you'll notice that the soil surface of your house plants is thinly coated with a white crusty substance (salts) and that a ridge of dirt and salts circles the inside of the pot rim, just above the soil surface. Alkaline water has a high pH factor that interferes with roots' absorption of nutrients, especially iron.
Annual repotting with fresh potting soils and bark will lower pH levels in the soil, making it easier for the house plants' roots to draw up nutrients.
Repot your house plants in spring, when they've either recently finished flowering (phalaenopsis and other orchids, shlumbergera or Christmas cacti), have just come out of winter dormancy (African violets and Cape primrose) or are about to show a growth spurt or to begin to set flower buds or stalks (succulents, ferns, spider plants).
Use sterilized potting soil that is formulated for the plant type. African violet soil mix contains higher levels of moisture-retaining peat than regular potting soil. Sandier cactus soil mix drains quickly so that cactus and succulent roots don't get soggy and rot. Replace dried-out orchid barks that no longer hold moisture with the same size pieces.
Newer formulations of potting soil contain beneficial bacteria and fungi that attach to the plants' roots and help draw up and retain water and nutrients.
Some brands of potting soils that are premixed with fertilizer don't show the percentages and types of macro and micro-nutrients in the product on the label. If that information is important to you, it's probably best to buy a regular potting soil and then fertilize on your own schedule.
To repot, gently remove the roots from pot and use sharp scissors to cut off roots that protruded from the drain hole. Orchids often produce a lot of roots that extend into the air. If those won't fit in the new pot, you'll need to cut them back. Break or cut compacted root balls apart.
The new pot should be one size larger, no more, or the roots will take a lot of time and energy to fill the pot.
Place a small square of fiberglass window screening (available at hardware centers) over the drain hole to prevent the soil from washing out. Rocks, Styrofoam pellets, broken pot pieces and other bulky materials can block the hole.
Fill the bottom of the pot with soil so that the plant's top soil surface stands about one inch below the rim. Then fill in the sides of the roots with damp soil or bark and water with tepid water. It will take about two weeks for the plant to adjust to the new pot and to begin growing into it.