How to Repot a Root-Bound Plant
Sooner or later every houseplant fills its pot. The roots reach the sides, turn, and start to circle, until the pot is more root than soil. Gardeners call this root-bound, or pot-bound. It sounds alarming, but it is a normal stage in a plant's life, and it is not always a problem. Here is how to tell when it matters and how to deal with it.
How to tell
A root-bound plant usually shows several of these signs:
- Roots growing out of the drainage hole or across the top of the soil.
- Water running straight through the pot and out of the bottom, because there is little soil left to hold it.
- Soil that dries out within a day or two of watering.
- Growth slowing or stopping in spring and summer, despite good light.
- A plastic pot bulging, distorting or even splitting.
To be sure, slide the plant out of its pot. If you see a dense mat of roots wrapped around the outside of the root ball, with little soil visible, it is root-bound.
When it is fine
Some plants grow happily when a little crowded and should not be rushed into a bigger pot. A crowded sansevieria is a common sight in our greenhouse, and it is perfectly healthy; these plants are often happier snug than swimming in soil. A ZZ plant is similar. It prefers a close fit, and its rhizomes will tell you when it is truly out of room by bulging or cracking the pot. When a ZZ plant does need more space, choose a pot only slightly wider than the rhizome mass. Many palms, peace lilies and spider plants also tolerate crowding well.
For these plants, repot only when the roots are clearly running out of room: soil drying out within days, or the pot starting to split.
When it is a problem
For most leafy plants, a badly root-bound plant cannot take up enough water or nutrients. It wilts quickly, drops leaves and stops growing. Circling roots can also start to strangle each other. These plants need a bigger pot, and the best time is spring or early summer, when they are growing actively and can push new roots into fresh soil quickly.
Step by step
- Water the plant the day before. Moist roots are more flexible and slide out more easily.
- Choose a new pot just one size larger, about two inches wider. A terracotta pot is a good choice for plants that like to dry out between waterings; plastic suits thirstier plants.
- Remove the plant. Squeeze a plastic pot or run a knife around the inside of a rigid one. If the roots have grown through the drainage hole, you may need to trim them or cut a plastic pot away.
- Loosen the roots. Gently tease the circling roots apart with your fingers so they point outward. If the mat is too dense, make three or four shallow vertical cuts down the sides of the root ball with a clean knife. It looks brutal, but it encourages new roots to grow out into the fresh soil.
- Trim any roots that are dead, black or mushy.
- Set the plant in the new pot at the same depth as before, fill around it with fresh mix, and firm gently.
- Water thoroughly and let it drain.
Our full repotting guide covers choosing the right soil for each type of plant and more detail on each step.
If you cannot go bigger
Sometimes a plant is already in the largest pot you want to manage. You can still relieve a root-bound plant without moving it up a size. Take it out, trim around a quarter of the root mass from the outside and the bottom, and replant it in the same pot with fresh mix around it. Done every couple of years in spring, this keeps a large plant healthy at a fixed size.
Moving to a different kind of pot
Repotting is also the easiest time to change the kind of pot a plant lives in. If a thirsty plant such as a fern keeps drying out, moving it into a self-watering pot at this stage, with the wick threaded up into the fresh soil, can make its care much easier.
Aftercare
Expect some drooping for a week or so while the roots recover. Keep the plant out of direct sun, and do not feed it for about a month. The biggest risk is overwatering: the new soil holds more water than the roots can yet reach, so check the soil before each drink and wait until the top inch or two is dry. Within a few weeks, new growth will show that the roots have found their new space.