How to repot a plant, step by step

Repotting is one of the few things that stresses a healthy plant. It's best done when it's needed, not just in case.

When to do it

• Roots are coming out of the drainage holes. The clearest sign.
• Water runs straight through without wetting anything: there's almost no potting mix left, only roots.
• The plant stopped growing in the middle of the growing season.
• It dries out very fast, a day after watering.
• The soil is compacted or has a white crust of salts on the surface.
• Suspected rot: in that case repotting is an emergency, with fresh, dry potting mix.

When not to

• Right after buying it. Give it two or three weeks to acclimate before changing anything.
• In the middle of winter. It's dormant and recovers less well. The best time is spring.
• While it's in bloom. Wait until it finishes.
• Species that bloom when snug: peace lily, African violet, orchids. Move them to a big pot and they stop blooming.

Step by step

1. Water the day before. With a moist root ball the roots suffer less and come out intact.
2. Choose the pot: just one size bigger, two to four centimeters (1 to 1.5 in) wider in diameter. With a drainage hole.
3. Prepare it: a layer of potting mix in the bottom, measured so the base of the stem sits a couple of centimeters (about an inch) below the rim.
4. Take the plant out: tip the pot on its side and hold the base of the stem. If it won't come out, squeeze the sides of the plastic pot or run a knife around the edge. Don't pull on the stem.
5. Check the roots: healthy ones are white or light-colored and firm. Cut off any that are black, mushy or smelly. If the root ball is wound around itself, loosen it with your fingers.
6. Set it in place and fill in around it with fresh potting mix, pressing gently. Don't pack it down: the roots need air.
7. Water thoroughly and let it drain.
8. Shade for a few days. Indirect light, no direct sun, while it recovers.

The giant-pot mistake

It's the most common one and it sounds reasonable: "I'll give it a big one and never have to do this again." The problem is that the potting mix the roots don't occupy holds moisture nobody uses, and that stagnant moisture rots the roots. One size up at a time.

After repotting

It's normal for it to look a bit droopy for a week or two. Don't fertilize during the first month: the fresh potting mix already has nutrients and the roots are damaged. If something starts to turn yellow, check why leaves turn yellow.