When it's time to repot a plant, the answer is almost always "one pot size up." Two sizes up is the most common mistake new plant owners make — and one of the fastest ways to accidentally kill a perfectly healthy plant. Here's why pot size matters, when to actually repot, and how to do it without losing the plant.

Why overpotting kills plants

It feels intuitive that a bigger pot would mean more room to grow, more soil, more water-holding capacity. None of that is wrong in principle. The problem is what happens to the water in the meantime.

A plant's roots can only absorb water from soil they're in contact with. When you put a small plant in a much bigger pot, most of the soil sits beyond the reach of the roots. That excess soil holds water like a sponge — and water sitting in soil that's not being absorbed becomes stagnant. Stagnant water suffocates roots. Suffocated roots rot. A rotted plant doesn't recover quickly, and sometimes doesn't recover at all.

This is why a plant that was thriving in a small pot can look unwell within a few weeks of being moved into a much bigger one.

When to actually repot

Most plants need repotting every 18 months to two years. Some prefer to be left alone for longer. The signs that a plant genuinely needs a bigger home:

• Roots growing out of the drainage holes. This is the clearest signal.
• Roots circling the base when you slide the plant out of its pot. A few circles is fine; tightly packed roots that look more like a basket than a root system is the time to act.
• Water runs straight through without absorbing. If the compost can't hold water, there's not enough of it left between the roots.
• Growth has slowed significantly despite good light, watering and feeding. The plant has run out of room.

If none of these apply, leave the plant where it is. Repotting is a stressor — only do it when the plant actually needs it.

How to repot, step by step

1. Pick the pot

2–3cm wider in diameter than the current one. Same depth, ideally with drainage holes in the base. If you want to use a decorative pot without drainage, plant the plant in an internal nursery pot (with drainage) that fits inside the decorative one — that way you can lift it out to water.

2. Prepare fresh compost

Peat-free, suited to the plant type. Most plants are happy in a general-purpose houseplant mix; cacti and succulents need a free-draining cactus compost; orchids need bark, not soil. Don't reuse old compost — it's depleted of nutrients and may carry pests or fungal spores.

3. Slide the plant out gently

Tip the pot sideways, support the base of the plant with one hand, and ease it out. If it resists, run a knife around the inside edge of the pot to loosen it. Never yank a plant out by the stem.

4. Tease the roots

If the roots are circling tightly, gently loosen the outer ones with your fingers. You're not trying to untangle them completely — just encouraging them to grow outward into the new compost rather than continuing in circles.

5. Pot up

Add a few centimetres of compost to the new pot. Sit the plant in, making sure the top of the root ball is about 1–2cm below the rim of the pot (leaves space for watering). Fill around the sides with compost, firm gently. Don't pack it down hard — roots need air pockets to function.

6. Water in, then leave alone

Water thoroughly so the new compost settles around the roots. Let it drain completely. Then place the plant somewhere bright but out of direct sun for a week, and resist the urge to water again until the top of the compost feels dry. The plant needs a few days to settle without being disturbed.

Frequently asked

Can I put a small plant in a big decorative pot anyway?

Yes — as long as you use a smaller plastic nursery pot (with drainage) inside the decorative one. The plant grows in the small pot, the decorative pot just holds it. Lift the inner pot out to water, let it drain, drop it back in. Best of both worlds.

When's the best time of year to repot?

Spring, ideally — the plant is actively growing and will recover from any root disturbance quickly. Summer is fine too. Avoid autumn and winter for non-essential repotting; the plant is in slower growth mode and recovers less well from stress.

Should I add stones to the bottom of the pot for drainage?

No — this is a persistent myth. Stones in the bottom of the pot actually impede drainage rather than help it. Use a pot with drainage holes and a free-draining compost; that's all you need.

Do I need to fertilise after repotting?

Not for the first month or two — fresh compost contains enough nutrients to keep the plant going. After that, switch to a normal feeding routine (balanced liquid feed every 2–4 weeks during the growing season, less often in winter).