The right pot size comes down to one principle: match the pot to the root ball, not the foliage. A pot that is too large holds excess moisture around the roots and encourages rot. A pot that is too small restricts growth and dries out within hours. Getting it right takes less guesswork than most people think.
The general rule is to go up one size when repotting, which means a pot 2 to 3cm wider in diameter than the current one.
Why Pot Size Matters More Than You Think
When a pot is significantly larger than the root ball, the excess compost stays wet for longer than the plant can use. This creates the conditions for root rot, especially in winter when growth slows and the plant absorbs less water. We see this in returns and care queries regularly as a small plant dropped into a large decorative pot, sitting in soggy soil for weeks.
On the other hand, a severely rootbound plant dries out within a day of watering, struggles to absorb nutrients, and eventually stops growing. If roots are circling the base of the pot or pushing out of drainage holes, it is time to size up.
The 2 to 3cm Rule
For most houseplants, go up by 2 to 3cm in internal diameter when repotting. If your current pot is 12cm across, move to a 14 or 15cm pot. This gives the roots room to grow without drowning them in unused compost.
For fast growers like Epipremnum or Monstera, you can stretch to 4 to 5cm wider. For slow growers like Sansevieria or Zamioculcas, stick to 2cm.
When Not to Size Up at All
Some plants perform better when slightly rootbound. Spider plants produce more babies when snug in their pots. Many cacti and succulents prefer tight fits because the soil dries faster. If the plant looks healthy and is growing well, there is no obligation to repot just because it has been a year.
In our experience, people repot too often rather than too rarely. If the plant is not showing signs of being rootbound, leave it alone.
Terracotta vs Plastic: How Pot Material Affects Sizing
Terracotta is porous and wicks moisture away from the soil, meaning compost dries out faster. This suits plants that prefer to dry between waterings: succulents, snake plants, and ZZ plants. Browse our ceramic and glazed pots for decorative options.
Plastic retains moisture longer, which suits humidity lovers like ferns and Calathea. If you are using plastic and the plant likes to dry out, you may want to stay with the same pot size rather than going up, to avoid waterlogging.
Clear pots are useful for monitoring root health and moisture levels, especially for orchids and aroids. You can see exactly when the roots need more space and when the compost is still wet.
Drainage Holes Are Non-Negotiable
Whatever size you choose, the pot must have drainage holes. A beautiful decorative pot without drainage should be used as an outer cover (cachepot) with a slightly smaller nursery pot inside. This also makes it easy to check for water pooling at the bottom. For a deeper look at why this matters, read our guide on whether pots really need drainage holes.
Signs You Have the Wrong Pot Size
Too large: soil stays wet for more than a week after watering. The plant looks lost in the pot. New growth is slow or absent despite good light and feeding.
Too small: water runs straight through the pot without soaking in (check our guide on why water runs straight through). Roots are visible at the surface or emerging from drainage holes. The plant wilts within a day of watering. Growth has stalled despite the right conditions.
When in doubt, err on the side of a slightly smaller pot. Most houseplants recover more easily from being slightly snug than from sitting in wet compost.