I’m interested in information about root pruning container plants. When and how? Do the plants have to be removed from the containers in order to do it? Do the cut roots need to be removed from the container too?
You will need to remove the container in order to prune the roots. Don’t leave cut roots in the container.
Ann Wheeler of Log House Herbs demonstrates how her root pruning technique in this Arbor Gate video.
According to Sunset’s Container Gardening (1998), fall is the best time to do this (when the plant is not in the height of the growing season). They suggest that a containerized plant can be root-pruned after 3 years or so. Here are the steps they recommend:
- Loosen the soil around the pot walls with a knife.
- Tap around the rim with a rubber mallet and then pull the plant free – OR:
- float the root ball out by forcing water from a hose through the drainage hole
- Examine the root ball and trim any twisted roots.
- Pull out and untangle large roots, and then use shears or a pruning saw to cut big roots back by 1/3 to 1/2.
- Scrub the inside of the pot with a stiff brush and plain hot water or a solution of 4 parts water to 1 part bleach. Rinse with clear water.
- Repot with fresh potting mix.