What Size Pot for Repotting? A Guide to Perfect Sizing
By Sara Linwood, houseplant writerLast updated
When repotting a houseplant, you should generally choose a container that is 1 to 2 inches (2.5 to 5 cm) larger in diameter than the current pot, or approximately 20% larger than the existing root ball. Selecting a pot that is too large can lead to a condition called 'over-potting', where excess soil stays wet for too long, significantly increasing the risk of root rot.
Why is choosing the correct pot size so important?
It is tempting to put a small plant into a large pot to 'let it grow into it', but this is one of the most common ways to kill a houseplant. Roots need a balance of water and air. When you have a small root system in a massive amount of soil, the plant cannot drink all the water held in that soil. The result is a cold, soggy mass of dirt that stays wet for weeks, which effectively drowns the roots.
On the other hand, keeping a plant in a pot that is too small leads to it becoming 'root-bound'. This means the roots have filled all the available space and there is very little soil left to hold moisture or nutrients. You might find yourself needing to water a root-bound pothos every two days just to keep it from wilting. Finding the 'Goldilocks' size is the key to a healthy, low-maintenance plant.
How do you pick a pot based on root ball size?
The best way to determine the new pot size is to look at the root ball itself, not just the foliage of the plant. A large plant with a small, compact root system (like a snake plant) needs a much smaller pot than a similar-sized plant with an aggressive, fleshy root system (like a peace lily). Use the following table as a general guide for sizing up.
| Root Ball Diameter | Current Pot Size | New Pot Size |
|---|---|---|
| 3 to 4 inches (7-10 cm) | 4 inch (10 cm) | 5 or 6 inch (12-15 cm) |
| 5 to 6 inches (12-15 cm) | 6 inch (15 cm) | 8 inch (20 cm) |
| 7 to 9 inches (18-23 cm) | 8 or 10 inch (20-25 cm) | 12 inch (30 cm) |
| 10+ inches (25+ cm) | 12 inch (30 cm) | 14 inch (35 cm) |
When you are ready to mix your new soil, use the soil mix calculator to estimate how much media you will need to fill the gap between the old root ball and the new pot walls. This helps prevent running out of soil halfway through the job.
Does the number of drainage holes matter?
Yes, the drainage hole is the most important part of any pot. Without a way for water to escape, gravity pulls all the liquid to the bottom of the pot, creating a swamp. Even if you use a fast-draining cactus mix, a lack of holes will lead to rot. If you find a decorative pot you love that has no holes, you should use it as a 'cachepot' (a decorative outer sleeve) and keep the plant in a plastic nursery pot inside it.
| Pot Diameter | Min. Number of Holes | Min. Hole Size |
|---|---|---|
| Under 6 inches (15 cm) | 1 hole | 0.5 inch (1.2 cm) |
| 6 to 10 inches (15-25 cm) | 1 to 3 holes | 0.5 to 0.75 inch (1.2-2 cm) |
| 10 to 14 inches (25-35 cm) | 3 to 5 holes | 0.75 inch (2 cm) |
| Over 14 inches (35 cm) | 5+ holes | 1 inch (2.5 cm) |
How deep should the new pot be for your plant?
Diameter is only half the story; depth also plays a major role in how soil dries. A deep pot holds a larger 'reservoir' of wet soil at the bottom, which is far from the surface where evaporation happens. This is fine for deep-rooting plants like a monstera, but it can be deadly for succulents or small tropicals with shallow root systems.
For most houseplants, look for a pot that is roughly as deep as it is wide. If you are repotting a succulent, look for an 'azalea pot' or a 'bulb pan', which are shallower than standard pots. These shorter containers allow the soil to dry out much faster, matching the needs of desert plants perfectly.
How do you correctly place a plant in its new pot?
Once you have selected the right size, the physical placement of the plant is the final step to ensuring long-term health. The biggest mistake is burying the plant deeper than it was before, which can cause the stem to rot.
Step by step
Proper Plant Placement in a New Pot
Time: about 20 minutes
You'll need
- New pot (1-2 inches larger)
- Fresh soil mix
- Trowel
- Watering can
- Add a base layer. Place 1 to 2 inches (2.5-5 cm) of fresh soil at the bottom of the new pot.
- Position the plant. Set the root ball into the pot. The top of the root ball should sit about 0.5 to 1 inch (1.2-2.5 cm) below the rim of the pot.
- Check the height. Ensure the soil line on the plant stem matches the previous soil line. Do not bury the stem deeper.
- Fill the gaps. Scoop soil into the space around the root ball, tapping the pot gently on the table to help the soil settle.
- Water and settle. Water the plant thoroughly until it runs out the bottom. This settles the soil around the roots and removes large air pockets.
Advice by situation
Slow-growing plants
For plants like zz plant, you can often stay in the same size pot and just refresh the soil every few years.
Top-heavy plants
Choose a heavy terracotta or ceramic pot that is slightly wider at the base to prevent the plant from tipping over as it grows.
Propagations
Move cuttings into very small pots (2 or 3 inches) first. Giving a small cutting too much soil room is the easiest way to cause rot.
Orchids
Orchids need specialized clear pots with side slits for maximum airflow; standard pot sizing rules don't apply to them.
Terrariums
Plants in terrariums should be kept in smaller pots or pruned frequently to restrict their growth and keep them from outgrowing the glass.
Common mistakes to avoid
- Jumping more than 2 inches in size. Stay within the 1-2 inch (2.5-5 cm) range to avoid over-potting and root rot.
- Using a pot without drainage holes. Always use a nursery pot inside a decorative pot if the outer one lacks drainage.
- Burying the stem too deep. Keep the new soil level the same as the old soil level to prevent stem rot.
- Packing the soil down too hard. Firm the soil gently but leave it porous so roots can breathe and water can move.
- Repotting a sick plant. Wait until a plant is healthy before repotting, as the process is stressful and can finish off a struggling plant.
- Using garden soil in a large pot. Large pots need even lighter, airier soil because they take longer to dry out; stick to high-quality indoor mixes.
Quick checklist
- Measure the current pot diameter.
- Select a new pot 1 to 2 inches (2.5-5 cm) wider.
- Verify the new pot has adequate drainage holes.
- Check the root ball for health before placing it in the new pot.
- Keep the soil line consistent with the previous potting.
- Leave 0.5 to 1 inch of space at the top for easy watering.
- Water immediately after repotting to settle the soil.
- Use a shallower pot for succulents and cacti.
Frequently asked questions
Can I put a small plant in a big pot if I don't water much?
It is still risky because the soil remains damp in the center for a long time, which encourages fungal growth even if the top looks dry.
When is the best time of year to up-size a pot?
Spring and early summer are best, as the plant is actively growing and will quickly expand its roots into the new soil.
What if my plant is very root-bound?
Gently loosen the outer roots with your fingers or a clean knife before putting it into the new, larger pot.
Do I need to put rocks at the bottom of the pot?
No, this is a myth. Rocks actually raise the water table. Use a pot with holes and good soil instead.
How do I know if my pot is too small?
If roots are growing out of the drainage holes or the plant needs water every day, it's time to size up.
What is a nursery pot?
It is the plain plastic pot (usually black or green) that plants come in when you buy them. They have excellent drainage.