My grandma was an avid gardener, and always told me late February was an ideal time for repotting houseplants here in the northern US. The reason is plants will start coming out of their winter dormancy soon, and they'll need fresh nutrients when they start putting out new growth. Plus it feels good to us gardeners to get our hands into dirt again after the long winter.
To remove most plants from their pot, turn the pot on it's side and gently tap against a hard surface. If it is a very large plant, pound the side with your fist to loosen it. This should allow you to lift the plant from the pot easily. Examine the roots, and if they are growing out the bottom of the pot, or the roots are solid and not much dirt remains, your plant is root-bound, and will need a bigger pot. It's a good rule of thumb to increase the pot size by 1 to 2 inches in diameter to allow for root growth. With most plants, you should also break up the roots, or score with a sharp knife, to encourage new root growth.
Some plants, such as the Boston and Asparagus Ferns can be divided to make additional plants when they become root-bound. First cut off the existing foliage - I know it's a hard thing to do, but you will end up with healthier plants in the end. With a sharp knife, cut the root ball into thirds. Then repot each section into a new pot. In no time, you will see new growth shooting up, and you'll end up with 3 plants instead of 1.
Repotting:
Soil - Purchase a good potting soil mix. Some plants such as cactus do better with a special soil mix just for them to get optimum results. Potting soil by itself doesn't provide many nutrients, so a fertilizer is recommended.
Pot - The new pot should be 1 to 2 inches larger in diameter than the old pot. It's best to use a pot with a hole in the bottom with a drainage tray or saucer, to avoid roots sitting in water. If you use a solid pot, place large stones or a large piece of a broken clay pot at the bottom for drainage. If using a terra cotta pot, pre-soak it in water so it doesn't wick water away from the new plant. Always wash a pre-used pot with soap and water before replanting.
Fertilizer - Some potting soil mixes will contain a time-released fertilizer. If yours doesn't, add a good fertilizer. Fertilizes come in liquid, granular, spikes, and many organic formulas are also available.
Planting - Put some new soil into the pot, and position the plant so that the previous soil level is approximately 1 to 1 1/2 inches below the rim of the pot. Then pour dirt in around the plant, packing it gently as you go. Be careful not to pack the dirt down too much, as you want the roots to be able to breathe. Bring the dirt level with where it was previously on the plant.
Water - In most cases, it's best to water from the bottom, putting water into the drainage saucer, and let the plant draw the water up into the pot. If using a pot that doesn't have drain holes in the bottom, be careful not to over-water it. The roots will rot if they sit in water.
Now put your newly potted plants in a sunny window, sit back and relax. Your plants will soon reward you with beautiful new growth shooting up.
