Houseplants Require Fresh Soil, Repotting

From The Fresno Bee, March 18, 2010, by Elinor Teague:

Houseplants are often taken for granted. We say thank you to Aunt Hilda for her thoughtful gift of an African violet, put it on the windowsill and water it when we remember, just often enough so that it lives. Even those of us who take better care of our houseplants--fertilizing every two weeks in the growth period, moving the plants' positions in the house as the light changes over the seasons and checking soil moisture levels every four or five days--often ignore the necessity of regular repotting.

Ideally, houseplants should be repotted before the roots have grown through the bottom drainhole and before new growth is stunted or non-existent. Fairly fast-growing plants such as African violets should be repotted every 4 to 6 months; plan on repotting slow-growing plants, including philodendrons and ficus benjamina, at least once a year. When repotting, always use a good-quality sterilized potting mix that is formulated for the plant type. Regular potting soil is fine for many plants but cactuses and succulents do best in sandy mixes, orchids generally are potted in orchid barks and shade-loving plants and African violets do well in acid-type mixes that contain a higher percentage of peat. Peat-based mixes dry out quickly in our summer heat. Check soil moisture levels for those plants more often. If the soil is hard, immerse the entire pot in tepid water until it is soaked. It may be best to replace the dried-out soil mix if the problem continues.

Even if the pot provides enough root space for the plant, the planting soil should be replaced annually. Potting soil mixes and orchid barks lose their ability to absorb and hold moisture over time. Adding more soil to fill the pot to the rim is not the solution. Instead, remove the plant from the pot and replace the soil in the bottom to raise the soil level.