Quick answer: Choose a pot 3 to 5cm wider in diameter than the current one and repot in spring, once roots circle the base or poke through the drainage holes. Going up gradually beats one big jump, because spare compost holds water the roots cannot reach, and that stagnant water is what causes rot.
Get plant pot sizing right and half of houseplant care quietly sorts itself out behind your back. Get it wrong and you spend months squinting at a perfectly healthy plant, wondering why it is sulking. I am Priya. I worked for several years on a garden centre nursery in Reading before I moved into plant-care writing, and I keep more than a hundred houseplants at home as ongoing experiments, much to my partner's despair. Friends send me SOS photos every week, and the answer is very often the pot. This guide is the sizing and repotting method I give them, step by step.
Why Pot Size Matters So Much
A pot is a plant's whole world. Too small and the roots circle, run out of food and dry out within hours of a good drink. Too big and the spare compost stays wet long after the roots have taken their fill, which is the fast lane to root rot. The Royal Horticultural Society advises potting on gradually, only a size or two up at a time, precisely to dodge that reservoir of cold, sour compost sitting around a small root ball (RHS, repotting houseplants).
The goal is simple, and I say it to every panicked friend: give the roots room to grow into over a season, not a swimming pool they will never fill.
The Sizing Rule in Centimetres
Pots are usually sold by their diameter across the top in centimetres. When you pot on, go up in modest steps, no heroics:
- Small plants (up to a 12cm pot): move up by about 2cm, so a 10cm plant slides into a 12cm pot.
- Medium plants (12 to 20cm pots): move up by 3 to 4cm.
- Large plants (20cm and above): move up by around 5cm.
A rough guide for how the finished thing looks: the pot wants to be roughly a third the height of the plant. A 90cm plant sits comfortably in a pot around 30cm tall. For statement plants and small trees that have reached their full size, our large plant pots and extra-large tree planters cover the top end most shops quietly ignore.
For seedlings, cuttings and anything you are propagating, do the exact opposite and stay small. A tiny root system rattling around a big pot is a miserable thing, so start them in something like the see-the-roots nursery pots and pot on as they fill out. Browse the full small pots range for windowsill and propagation sizes.
Six Signs Your Plant Needs a Bigger Pot
You do not repot on the calendar, you repot on need. Watch for these tell-tales:
- Roots poking out of the drainage holes. The clearest signal of the lot.
- Water runs straight through without soaking in, because the pot is more root than compost.
- The plant dries out within a day of a proper watering.
- Roots circling the surface or slowly lifting the plant up out of its pot.
- Growth has stalled in the growing season despite decent light and feeding.
- The pot is bulging or misshapen under the pressure of the root ball inside.
Most houseplants need potting on every one to two years, best done in spring as growth wakes up.
How to Repot, Step by Step
- Water the plant a day before. A hydrated root ball slides out clean and handles the upheaval far better.
- Choose the next size up, with a drainage hole, and have fresh peat-free compost ready to hand.
- Ease the plant out. Support the base, tip it, and slide. Do not yank the stem like a stubborn weed.
- Tease the roots gently. If they are tightly circled, loosen the outer ones so they head outward, not round and round.
- Part-fill the new pot, sit the plant so the old soil line stays just below the rim, then fill round the sides and firm it lightly.
- Water in well and let it drain. Then, and this is the hard part, leave it be.
Avoiding Repotting Shock
Plants can sulk for a week or two after a move, and that is entirely normal. You can keep it to a minimum:
- Repot in spring or early summer, in the plant's active season, when it can bounce back.
- Keep it out of harsh direct sun for a few days afterwards.
- Do not feed straightaway. Fresh compost has plenty to be going on with; hold off a few weeks.
- Water when needed, not on a fixed timer. A newly potted plant in fresh, moisture-holding compost needs far less than your instincts insist.
Gardeners' World note that most shop-bought houseplants arrive in a plastic nursery pot and are happier moved into a slightly larger home before long (Gardeners' World, repotting).
Matching the Pot to the Plant
Sizing is only half the tale. The right pot for a fern is the wrong pot for a cactus, because their thirst and drainage needs pull in opposite directions. For a species-by-species view once you have the sizing sorted, see my best pots for every plant guide. And whatever the size, drainage decides whether all this effort pays off at all, which is covered in Ted's care and drainage guide.
Pot size by plant type
| Pot diameter | Suits | Examples |
|---|---|---|
| 6 to 9cm | Seedlings and cuttings | Rooted cuttings, succulents, young herbs |
| 12 to 15cm | Small houseplants | Pilea, peperomia, kitchen herbs |
| 17 to 21cm | Medium houseplants | Young monstera, pothos, ferns |
| 24 to 30cm | Large houseplants and veg | Fiddle leaf fig, tomatoes, courgettes |
| 40cm and up | Shrubs and small trees | Olive trees, bamboo, patio fruit trees |
Frequently Asked Questions
How much bigger should a new pot be when repotting? Only one size up, roughly 2 to 5cm wider in diameter depending on the plant's size. Jumping several sizes leaves too much wet compost around the roots and risks rot.
When is the best time to repot a houseplant? Spring or early summer, when the plant is actively growing and can recover quickly. Avoid repotting in the depths of winter when growth has slowed right down.
Can a pot be too big for a plant? Yes. An oversized pot holds more water than the roots can use, so the compost stays soggy and roots can rot. Pot on gradually rather than giving a small plant a huge home in one go.
About the author Priya Nair - The right pot for every root Priya worked for several years at a garden centre nursery in Reading before moving into plant-care writing, and studied horticulture part-time along the way. She is fascinated by how material, size and drainage affect a plant's health, and keeps over a hundred houseplants as ongoing experiments. Friends send her SOS photos of dying plants weekly. Writing for Potty for Plant Pots.