Transplanting house plants is an often abused practice. It should only be done when the plant is truly potbound. Instead, house plants are often repotted when something is wrong with them. This practice can kill the plant. In the short run, transplanting is harmful because roots are broken and injured. A healthy plant will grow out of the initial harmful period. An unhealthy plant may already have damaged roots so may be killed by transplanting. House plants the problems should be transplanted after the problem is corrected and the plant is healthy.
Transplanting is done when a plant becomes potbound. Some plants grow best if slightly potbound, so should not be transplanted too soon. Several clues may be used to determine when a plant needs repotting. The best method is to take the plant out of the pot and look at the roots. If a mass of roots and but little soil is visible, the plant needs repotting. If the soil falls off the root ball, don't repot. Other clues may be used but may not be reliable. Roots growing out the drainhole is sometimes suggested as guideline. Roots often grow out the drainhole even when the plants are not potbound. The failure of a plant to grow or bloom with other plant of the same type is another clue. Especially if the plant does not grow during a normal growth period or fails to bloom when it should. However other reasons may cause a plant to fail to grow.
Transplanting is done before a growth period in spring or early summer. Use only the next size larger pot. Use of an excessively large pot may lead to overwatering. Use the same type of soil the plant is already growing in. Two different soil types may dry out at different rates and create watering problems.
Used pots should be washed with soap and water. Salt accumulation in the pots can be removed by soaking in water. Before using a new pot soak it in water to keep it from absorbing soil moisture.