All plants have a “root to shoot” ratio; both elements must be balanced in order for one to support the other. Mature plants grow more slowly than young ones, but they will still outgrow their pots.
As plants age and their root systems expand to fill their pots, the soil is literally squeezed out of the base, leaving progressively less to provide water and nutrients. This may even be the case when a plant is first purchased, with the root ball being so congested that roots are protruding through the base of the pot.
In this case, removing the pot in the conventional way may damage the roots because they are dragged back through the holes in the base. Instead, it is better sacrifice the pot by cutting it away using strong scissors or pruners, or break it off in the case of clay. Any long roots will soon re-establish once the plant has more room to grow in its new container.
With established plants, the growth rate of the roots is directly related to the rate of the top growth. This is called the “root to shoot” ratio. Trimming back the main roots will control the top when the plant has reached the desired size. This is useful when you do not have the space to accommodate a new, larger pot.
Top-dressing a mature plant
Removing a plant from its pot, however briefly, can cause it stress. Mature plants find this more difficult to cope with than young ones.
As an alternative to repotting a mature plant on a regular basis, which causes disturbance, you can rejuvenate it by top-dressing it instead. Outdoors, this involves applying a fertilizer around the base of a plant, but indoors it means adding new potting soil as well, at least in the upper part of the pot.
The plant can then stay in place for up to two years before it needs repotting completely. The old soil is gently scraped away with a small rake or fork and discarded, to be replaced by the same amount of fresh soil mix, usually one that contains a slow- release fertilizer.