Repotting most container-grown plants should be done annually, at the first signs of the spring flush of growth. (Bromeliads and other epiphytes are an exception.) In some cases, however, you won’t want to graduate to a larger pot, but keep the plant in the same size container. Here are some of these conditions:
- The plant is already its mature size
- You don’t have room for the plant to grow any larger
In either of these cases, you will want to repot into the same size container the plant was originally growing in. Even if this seems like an extra step, or busy work, don’t skip it! Potting media does not last forever, and plants in compacted, old potting mix will eventually succumb.
Root Pruning: Repotting without Potting Up
The secret to successful repotting is root pruning. This technique is very similar to the one used by bonsai enthusiasts to maintain their plants in shallow containers. To root prune:
- Lightly water the plant and wait an hour, then gently remove the plant from the container.
- Inspect the roots. Roots circling the inside of the pot are looking for air. In extreme cases, the soil inside the root ball might be gone.
- Using sharp snippers, cut away up to 2/3 of the root mass, beginning at the bottom and outside of the root ball. Remove dead roots and masses of fine roots, leaving large central roots intact.
- Place the root-pruned plant in a container with fresh potting mix, then add more potting until the roots are buried again.
- Using a long toothpick or chopstick, work soil into the open spaces between the roots. Gently water, then work in more soil, until you’re confident the plant is firmly situated in the new container.
- Remove the plant to a shadier location and keep moist until it recovers. Root-pruned plants will typically go into shock for a few days and may look wilted or sulky. Keep the soil moist, and if you desire, use a root-stimulating solutions such as SuperThrive or another rooting solution. It should recover after a week, then begin to grow aggressively.
Plants that have been root-pruned should suffer no adverse, long-term consequences, provided they have enough roots left to re-establish themselves and begin to grow again. Once the plant has perked back up, move it back to its normal position and enjoy the new flush of growth.