How to repot a houseplant: when to do it, pot size, potting mix and aftercare

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Repotting gives a houseplant fresh compost and room to grow. It is not something most plants need often, and repotting too often or into too big a pot causes more problems than it solves. Here is how to tell when it is time and how to do it with as little stress as possible.

Signs a plant needs repotting

Roots are growing out of the drainage holes or circling the surface
Water runs straight through without soaking in, or the plant dries out within a day or two
The plant is top-heavy and tips over
Growth has stalled in the growing season despite good light and care
The compost has broken down, shrunk or become hard and crusty

If you slide the plant out and see a solid mass of roots with little compost visible, it is root-bound. Many plants are repotted every year or two when young and less often when mature. Some, such as snake plants and many succulents, are happy being fairly snug.

When to do it

Spring and early summer are best, as the plant is growing actively and recovers quickly. Avoid repotting in winter unless there is an emergency, such as root rot. Also avoid repotting a plant that is flowering or one you have just brought home; let it settle into its new spot for a few weeks first.

Choosing the pot

Go up only a little: a pot about 2 to 5 centimetres (1 to 2 inches) wider than the current one is usually right. Too large a pot holds a lot of wet compost the roots cannot reach, which can lead to root rot.
Drainage holes are essential. Use a decorative pot without holes only as an outer cover.
Terracotta dries quickly, which suits succulents and people who overwater. Plastic and glazed pots hold moisture longer.

If the plant has reached the size you want, you can repot it into the same pot with fresh compost, trimming some outer roots to make room.

Potting mix

Use a fresh compost made for indoor plants rather than garden soil, which compacts in pots and can bring in pests. Different groups prefer different mixes:

Most leafy houseplants: a general houseplant compost, often loosened with perlite.
Aroids such as monstera and philodendron: a chunkier, airy mix with bark and perlite.
Cacti and succulents: a gritty, fast-draining mix.
Orchids: a bark-based orchid mix, not ordinary compost.

Step by step

Water the plant a day or so beforehand, so the root ball holds together and the plant is not stressed.
Prepare the new pot with a layer of fresh compost in the bottom, enough to bring the top of the root ball to roughly the same level as before, a little below the rim.
Tip the old pot on its side, support the base of the stems, and ease the plant out. Squeeze a plastic pot or run a knife around the inside edge if it sticks. Do not pull by the stems.
Gently loosen circling roots with your fingers. Trim any that are dead, black or mushy with clean scissors.
Set the plant in the new pot at the same depth it was growing before. Burying the stem deeper can cause rot.
Fill around the sides with compost, firming gently to remove large air pockets without packing it hard.
Water thoroughly until it drains, then top up any compost that settles.

Aftercare

Put the plant back in its usual spot, out of harsh direct sun for a week or so.
Some drooping is normal for a few days.
Wait until the top of the compost dries before watering again; fresh compost often holds more water than you expect.
Hold off on fertiliser for a few weeks, as fresh compost usually contains some nutrients.

If a plant is struggling with root rot, remove all the old wet compost, cut away the rotten roots and replant in fresh, barely damp compost in a clean pot that fits the healthy roots. What are you planning to repot next, and what went well or badly last time? Share your questions and experiences in the comments.