Measure plant height
From compost surface to the top of the foliage.
Pot Size Calculator
Enter your plant’s height for a suggested pot diameter, plus practical container-growing advice to avoid waterlogging and tip-overs.
Calculator
Tap a screen and type with the keypad (or your keyboard), choose an option, then press =. The answer shows on the calculator screen, with full details underneath.
Garden Plant Finder
POT SIZE · GPF
How to measure
Follow these steps for accurate inputs and better results.
Check the root ball
If roots circle the pot, size up even if height seems modest.
Pick diameter
Use the calculator suggestion, then confirm stability for tall plants.
Ensure drainage
Holes plus free-draining compost are non-negotiable.
Why this matters
Pots that are too small dry out and starve roots; pots that are too large stay wet and invite rot.
Correct sizing improves flowering, reduces tipping, and makes watering more predictable.
A quick height-based guide helps beginners buy the right container first time.
Common mistakes
No drainage holes
The fastest route to root rot.
Jumping many sizes
Huge empty compost volumes stay cold and wet.
Lightweight tall pots
Wind topples top-heavy plants — add weight or a wider base.
Potting too deep
Burying stems can cause rot on many shrubs.
Ignoring saucer water
Empty standing water after watering.
Tips from gardening experts
Leave headspace
2–3 cm at the top makes watering cleaner.
Use quality peat-free compost
Match ericaceous compost to acid-lovers.
Feed in the growing season
Container nutrients wash out — use a suitable feed.
Group pots
Clustering reduces watering stress in heat.
Frequently asked questions
What size pot for a 50 cm plant?
Often around 25–30 cm diameter, depending on root ball and species.
Should pot size match height or roots?
Both matter — height guides stability and visual balance; roots decide whether you must size up now.
How often should I repot?
Many plants every 1–2 years, or when roots fill the pot.
Can a pot be too big?
Yes — excess wet compost can harm roots. Step up gradually.
Do terracotta pots dry faster?
Yes — they are breathable. Plastic holds moisture longer.
What about self-watering pots?
Useful for holidays, but still check reservoirs and avoid constant saturation for drought-lovers.
How deep should a pot be?
Deep enough for the root system; tall pots help deep-rooted shrubs, bowls suit shallow herbs.
Can I reuse old compost?
Refresh with new compost and grit; don’t reuse if disease was present.
Why does my pot plant wilt after watering?
Could be root rot from waterlogging, or heat stress — check drainage and root health.
What size pot for lavender?
A compact lavender often suits 25–30 cm with very free-draining mix.
Sources and further reading
Want more detail? These pages from the Royal Horticultural Society (RHS), the UK’s gardening charity, explain the topic in depth.
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Downloads
Repotting checklist
When and how to size up safely.
Container compost PDF
Placeholder mix ideas.
Get seasonal gardening advice
See what to sow, plant and prune each month in the Garden Plant Finder seasonal calendar.
Ready to choose plants?
Use Plant Finder filters for soil, sun, wildlife and flowering month — then plan quantities with these calculators.