Houseplants slowly fill their pots with roots. Eventually there is more root than potting mix, the pot dries out quickly after watering, and growth stalls. Repotting fixes that, but it isn't a cure-all, and a plant that is struggling for another reason can get worse from the disturbance. Check that the roots are actually the problem first.

The short answer

  1. Repot when roots have filled the pot: circling around the root ball, matted at the bottom, or growing out of the drainage holes, with mix that dries out fast.
  2. Do it in spring, as the plant starts growing again, not in the dim months of winter.
  3. Go only one or two inches wider, in a pot with drainage holes.
  4. Loosen circling roots by teasing them apart, or score a tight root ball with a knife.
  5. Water thoroughly, then wait until the plant needs water again, and hold off on fertilizer for two to four weeks.

Does it need repotting?

Slide the plant out of its pot and look. Most come out cleanly if you turn the pot on its side, support the base of the stems, and tap or squeeze the pot.

Signs it is time:

  • Roots circle around the outside of the root ball, or are so dense in the bottom third that you can barely see any mix.
  • Roots are growing out of the drainage holes, and the pot is crowded with them when you look.
  • The mix dries out very quickly after a thorough watering.
  • Growth has stalled even with good light and regular feeding.

One root poking out of a drainage hole is not enough evidence on its own. And look at the roots' condition as well as their quantity: healthy roots are white or light and firm, while soft, brown, mushy roots mean root rot, which a bigger pot will not fix. The yellow leaves guide explains how to inspect the roots.

When to repot

The best time is spring, when the plant naturally starts its season of growth and will grow new roots into the fresh mix quickly. In fall and winter, most houseplants grow slowly in the low light, and new mix around a barely growing root system stays wet. The guide to houseplant care in winter suggests waiting for spring unless a plant is badly root-bound or its mix stays waterlogged.

Choose the new pot

Go one or two inches wider than the current pot. A much larger pot surrounds the roots with mix they cannot reach yet, and that mix stays wet long after the roots have taken what they need.

Make sure it has drainage holes. A decorative pot without them can hold a plain nursery pot inside it, as long as you empty the water that collects at the bottom. Cover the hole with a piece of screen or a coffee filter if mix washes out; don't add a layer of gravel, which keeps the bottom of the pot wetter, as the container guide explains.

Use fresh potting mix, not garden soil, which packs down and drains poorly in a pot.

Step by step

  1. Remove the plant from its old pot, supporting the base of the stems.
  2. Loosen the roots. Gently tease apart roots that are matted or circling, so they will grow outward into the new mix. If the root ball is too tight to loosen by hand, score it with a knife in a few places down the sides.
  3. Trim any dead, soft, or broken roots.
  4. Set the plant at the same depth it grew before, on a layer of fresh mix in the new pot.
  5. Fill around the root ball with mix, firming it gently with your fingers. Leave space at the top of the pot so water can sit there and soak in.
  6. Water thoroughly until it runs out of the bottom, then let it drain.

Keeping a plant the same size

Not every plant needs a bigger pot. If a plant is already as large as you want it, or as large as its spot allows:

  • Root-prune and return it to the same pot. Remove the outer section of the roots, or cut vertically down the sides of the root ball to break up circling roots, then replant it in the same pot with some fresh mix. Cut back some of the top growth at the same time, so the plant isn't carrying more leaves than its reduced roots can support.
  • Top-dress containers too big to repot. Scrape away the top two or three inches of old mix and replace it with fresh mix every other year or so.

Aftercare

  • Water, then wait. After the first thorough watering, don't water again until the plant needs it. The new mix may dry at a different rate from the old, so check it by feel for the first few weeks.
  • Hold off on fertilizer for two to four weeks. Most potting mixes contain a small amount of fertilizer, and freshly disturbed roots don't need more.

If the plant keeps wilting while the mix is moist, check the roots again; the Plant Doctor can help narrow down the cause.

Sources and further reading