Drainage Holes in Pots: How to Check Containers Before Planting

Illustration of a patio with a variety of planted containers

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Checking for drainage holes before planting is one of the most critical steps in container gardening. Without a way for excess water to escape, pots can quickly become waterlogged, leading to root rot and plant death. Proper drainage ensures that the potting medium remains aerated and that the root system can breathe, which is especially vital during the wetter UK winter months.

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Why drainage holes are essential

In a garden bed, excess water naturally percolates down through the soil profile. In a container, the water is trapped by the base of the pot. If there are no holes, the compost becomes saturated, displacing the oxygen that roots need to survive. This anaerobic environment allows root-rotting fungi to thrive, often manifesting as yellowing leaves or a sudden collapse of the plant despite the soil being moist.

While some plants prefer more moisture than others, almost all container-grown species—from seasonal bedding and bulbs to shrubs and small trees—require a mechanism to shed surplus water. This is particularly important for drought-tolerant plants, such as Mediterranean herbs, which are highly susceptible to rot if left in standing water.

How to check your containers

Before filling a pot with compost, perform a physical inspection of the base. Do not assume a pot has drainage simply because it is sold as a ‘planter’.

Visual inspection: Tip the pot over and look at the bottom. You should see one or more clear openings.
Tactile check: Inspect carefully for blocked holes and sharp moulding or metal edges; remove debris with a suitable brush or tool.
Repurposed items: If you are using recycled materials such as tin baths, Belfast sinks, or wooden crates, inspect their existing outlet or drainage first. Only modify a container if its material and maker’s instructions permit safe drilling; otherwise use it as an outer pot with a removable, drained inner container.

Managing different hole sizes

The size of the drainage hole determines whether you need to add a protective layer before adding compost. The goal is to allow water to exit while keeping the growing medium inside the pot.

Small drainage holes

If the holes are small, the surface tension of the compost and the density of the mix are usually enough to keep the soil in place. In these cases, you can plant directly into the container without any additional base layer.

Large drainage holes

When a pot has a single large hole or several wide openings, compost can wash out during watering, leaving gaps in the soil and creating a mess on your patio. To prevent this, cover the holes with a permeable barrier. Suitable materials include:

Crocks: Broken pieces of terracotta pots.
Stones: A suitably sized piece that bridges the opening without plugging it; do not fill the bottom with a gravel layer.

Practical Example: If you have a large pot with a single drainage hole measuring 3cm in diameter, this exceeds the recommended 2.5cm threshold. By placing a few pieces of broken terracotta (crocks) over the hole, you create a filter that allows water to flow through while preventing the peat-free compost from leaking out.

Material-specific drainage considerations

The material of your container affects how water moves through the system, which may influence how you manage drainage.

Material	Drainage Characteristic	Precaution
Terracotta/Clay	Porous walls allow some evaporation.	Dry out faster; ensure holes are clear to avoid winter waterlogging.
Plastic	Non-porous; water only exits via holes.	Prone to waterlogging if holes are too few or too small.
Metal	Non-porous and can heat up.	Needs clear drainage and protection from excessive root-zone heat.
Wood	Naturally permeable but rots over time.	If lining with plastic, you must punch holes through the liner.

Diagnosing and preventing waterlogging

Even with drainage holes, a pot can still become waterlogged if the exit is blocked or the pot is sitting in a pool of water. This is a common issue during the UK winter.

Signs of poor drainage

Water pooling on the surface of the compost for long periods after watering.
A ‘sour’ or anaerobic smell coming from the soil.
Mushy, brown roots when the plant is lifted from the pot.

Preventative measures

To ensure the drainage holes can actually function, check whether the base sits flush over the outlets. Stable pot feet can keep holes clear where necessary; not every pot needs raising.

Pot feet: Use dedicated plastic or terracotta feet to lift the pot.
Bricks: Placing a pot on bricks provides a gap for water to flow away.
Winter care: Remove any saucers or trays during the winter months. While saucers are useful in summer to catch excess water and maintain humidity, they can cause pots to stand in water during rainy seasons, effectively cancelling out the benefit of the drainage holes.

The risk of overpotting and drainage

Drainage is not just about the holes in the bottom, but also the volume of compost relative to the plant. ‘Overpotting’ occurs when a plant is placed in a container that is significantly larger than its rootball.

In an oversized pot, the excess compost holds more water than the plant’s roots can absorb. This creates a zone of permanently damp soil at the bottom of the pot, which can lead to root rot even if the container has drainage holes. As a general rule, choose a pot that is only slightly larger than the rootball of the specimen plant.

Useful products for this job

The links below open Amazon UK product searches. Check the exact item, seller, current price and compatibility before buying.

Pot feet: Used to raise containers off the ground to ensure drainage holes are not blocked. Ensure the size and weight capacity match the pot being lifted. Search Amazon for Pot feet.
Peat-free multipurpose compost: The standard growing medium mentioned for use in drained containers. Verify it is specifically for containers/potting rather than garden soil improvement. Search Amazon for Peat-free multipurpose compost.

Related garden guides

Sources and further guidance

Guidance researched in September 2026. The feature image is an AI-generated illustration. Product guidance is based on published information, not hands-on testing.