How to repot a houseplant, step by step

Over time potting compost breaks down and packs tighter, so less air reaches the roots (RHS), and roots fill the pot until water runs straight through. Repotting fixes both. The two most common mistakes are a pot that's far too big and a layer of gravel in the bottom; the steps below avoid both.

How much bigger should the new pot be?

Sources give slightly different figures, so here they are side by side. All of them say go up a little, not a lot: the RHS warns that bigger jumps risk overpotting.

For a typical houseplant in a pot up to 25 cm across, the overlap of these figures is about 2.5 to 5 cm wider. That's our reading of the four sources, not a rule from any one of them.

How to repot

1. Water the plant an hour before you start.

   

   Penn State Extension says to water the plant in its old pot and let it rest for one hour. Moisten the new potting mix as well, so it takes up water evenly later (Penn State). Spread newspaper on the table.

   You should see: mix that feels damp but not dripping when you squeeze a handful.

2. Cover the hole in the new pot and add a little mix.

   

   Lay the mesh or a piece of coffee filter over the drainage hole, then add a layer of slightly moist mix (Colorado State). Don't add a layer of gravel or crocks first. Illinois Extension calls the idea that gravel improves drainage a myth: water collects in the soil just above the gravel until that soil is saturated, and only then drains into it.

   You should see: the hole covered, and a few centimetres of loose mix on the bottom of the pot.

3. Ease the plant out of its old pot.

   

   Spread your fingers over the compost around the stems, turn the pot over and let the root ball slide into your hand (Colorado State). Don't pull the plant out by its stems or leaves. If it sticks, lay the pot on its side and tap or squeeze it (RHS). If it still won't move, a plastic pot can be cut away.

   You should see: the root ball in one piece in your hand, roots showing round the outside.

4. Careful: keep as many healthy roots as you can. Cut only roots that are dead, rotted or badly circling.

   Loosen circling roots and cut off any rotten ones.

   

   Gently tease the roots loose (Penn State). If they are tightly bound, score the root ball in a few places with a sharp knife (Colorado State). Cut away black, mushy roots (Colorado State); healthy roots are firm.

   You should see: root ends hanging free instead of wrapped round the ball, and no soft, dark roots left.

5. Set the plant at the same depth as before.

   

   Add or remove mix underneath until the top of the root ball sits about 2.5 cm (1 in) below the rim (Penn State), at the depth it grew before (Colorado State). That gap leaves room to water. Don't bury the stems deeper than they were.

   You should see: the plant upright in the middle, with its old compost level a little below the rim.

6. Fill round the sides and firm lightly.

   

   Fill the gap with mix and tap the pot to settle it (Colorado State). Firm the top lightly, without packing it hard (Penn State). The RHS says to firm enough to remove air pockets, and not to pile compost against the stems.

   You should see: no gaps down the sides, and a level surface about 2.5 cm below the rim.

7. Water until it drains, then top up any sunken mix.

   

   Water thoroughly and let it drain well (Penn State). If the mix settles below the top of the root ball, add a little more (Colorado State). Then put the plant back where it lives (Penn State).

   You should see: water running from the hole, and the root ball still covered.

If something goes wrong