House plants should be checked in early spring to see if they need repotting. Flowering plants usually need to be changed to a larger pot at least once a year. Some foliage plants can be kept in the same size pot two years or more, and slow-growing cacti and succulents can go even longer. Spring is the best time to repot house plants if they need it.
To find it out if the plant needs repotting, remove it from its pot. Turn it upside down, tap the rim of the pot on the table to loosen the soil ball and let it slide out of the pot into your hand. The soil should be neither wet nor dry when this is done, sort of in between.
If there's a mat of roots on the outside of the soil ball, the plant usually needs to be repotted.
Usually plants in three-inch pots are changed to five-inch ones, while those in larger pots are moved to the next size, for example, from five to six, from six to seven and so on. Pots are measured across the top.
Plants in fairly large pots may not require a larger pot but should be given some fresh soil. Remove the shoulder of soil around the top and some loose soil. To remove soil from around the roots, squeeze it gently to avoid breaking tender white roots.
The new pot should have a hole or holes in the bottom for drainage. Too much water is as bad or worse than not enough -- it may cause root rot.
Soil for house plants is important, but this can be overdone. Potting soil from a garden center is good enough, as is good garden soil well mixed with compost.
Put broken pieces of a clay pot or pebbles over the drainage hole to prevent soil from washing out when the plant is watered. But don't let them stop up the hole.
Firm the soil gently around the ball but avoid pressing too hard. This would compact the soil and reduce aeration. Water soon after repotting.
When you've finished repotting, the soil surface should be about half an inch below the rim of a three-inch pot and about one inch below that of a five- to eight-inch pot. This provides an area for watering, usually just large enough to hold sufficient water to wet the entire soft ball.
Plants in large tubs can be top-dressed for several years instead of repotted. To top-dress, remove the upper two inches of soil, including roots, and replace with fresh potting soil.