Choosing the right pot size
Also known as Overpotting, Potting up, Pot sizing
In short
A bigger pot is not a kinder pot. When there is far more potting mix than roots, the unused mix stays wet for a long time, roots sit in airless, soggy media and root rot becomes much more likely. Step up only about one size, roughly 2.5–5 cm (1–2 in) wider than the old pot.
How it looks
An overpotted plant is a small root ball sitting in a large volume of mix: after watering, the pot stays heavy and the mix stays dark and damp for many days, often with a band of wet mix around and below the roots that no roots have reached. A plant that genuinely needs a bigger pot shows the opposite: roots circling the inside of the pot or poking out of the drainage holes, a dense root ball with little visible mix, and mix that dries out very quickly even in cool weather. Lifting the plant out of its pot is the most reliable way to tell.
Signs
In an oversized pot: slow or stalled growth, yellowing lower leaves, wilting even though the mix is wet, a sour smell, and soft brown roots (root rot). In a pot that is too small: needing water very often, wilting soon after watering, roots growing out of the drainage holes, stunted growth despite regular feeding.
What favours it
Overpotting problems are worse with dense, water-retentive mixes, pots without drainage holes, cool or dim conditions where the plant uses little water, and plants that naturally have small or fine root systems. In warm, humid tropical homes growth is fast, but a mix that never dries is still a root-rot risk.
Prevention
- When potting up, choose a pot only about 2.5–5 cm (1–2 in) wider than the current one (Clemson); the RHS suggests the new pot should be no more than one third larger.
- Only pot up when roots fill the current pot (circling roots, roots through the drainage holes, mix drying very fast).
- Use a pot with drainage holes and a free-draining, soil-less potting mix.
- Water according to how dry the mix is, not by the calendar, especially after moving a plant into a larger pot.
Treatment
Start with the first step and move down only if the problem persists.
- If a plant is already in a pot that is far too large and the mix stays wet, move it back into a pot just larger than its root ball with fresh, free-draining mix.
- Check the roots when you do: trim away any soft, brown, rotten roots with clean tools.
- Until it re-establishes, water only when the upper mix has dried and avoid fertilising a struggling plant.
Pros and cons
Pros
- Stepping up gradually keeps the ratio of roots to mix balanced, so the mix dries at a healthy rate and roots get oxygen.
- A snug pot makes it easier to judge when to water.
Cons
- Small steps mean repotting fast-growing plants more often (fast growers may need it yearly, slow growers every 2–3 years).
- A pot that is too small dries out very quickly and can restrict growth.
Look-alikes
- Underwatering
- An underwatered plant wilts with dry, light, pulling-away mix; an overpotted plant often wilts while the mix is still wet.
- Root rot
- Root rot is the disease that overpotting often leads to; you see soft, brown, smelly roots when you unpot the plant.
- Overwatering
- Overwatering is about watering too often for the conditions; an oversized pot makes the same watering routine act like overwatering.
Typical uses
All container plants; especially important for houseplants with fine roots, succulents and cacti, orchids and other epiphytes, and any plant grown in a dense, peat- or coir-rich mix.
Related
Sources
- How to repot a plant — RHS
- Tips for Repotting Houseplants — University of Illinois Extension
- Houseplant Care — University of Wisconsin–Madison Extension
- Indoor Plants – Transplanting & Repotting — Clemson Cooperative Extension HGIC
- Prevent Root Rot Problems on Houseplants — Iowa State University Extension
- Properly Watering Container Houseplants — Virginia Cooperative Extension
Written in our own words from these sources. Check a product label before using any treatment.