Garden drainage: how to prevent waterlogging

Waterlogging: a growing problem

After every heavy downpour your lawn turns into a lake. The borders are a mud bath. And the shed smells damp. Sound familiar? Climate change means heavier rainfall in shorter bursts, and many gardens simply can't cope. Drainage is the fix, but not every garden needs it. Let's work out if yours does.

Tools like GardenWorld let you visualise your garden after a redesign. But underground work like drainage should be planned before you touch the surface.

Do you need drainage?

Try the hole test: dig a pit 30 x 30 cm and 30 cm deep. Fill it with water and watch. Empty within an hour? Your soil drains fine. Still half-full after four hours? You have a drainage issue.

Causes of waterlogging

• Clay soil: holds water like a sponge
• Compacted ground: years of foot traffic have destroyed the structure
• High water table: water rises from below, not above
• Too much hard surface: rainwater has nowhere to go

Drainage helps with clay and compacted soil. A high water table is trickier — the water just comes back. Raised beds and adapted planting may be more effective in that case.

Types of drainage

Land drain

The most common solution. A perforated plastic pipe (80–100 mm diameter) wrapped in geotextile, laid in a gravel bed. Water enters through the perforations and flows to a soakaway, ditch or storm drain.

French drain

A gravel-filled trench without a pipe. Simpler to install but less effective in heavy rain. Good as a supplement or for localised wet spots.

Soakaway crate

An underground plastic crate that collects water and lets it slowly infiltrate. Ideal as the endpoint of your drainage system. Available at RHS garden centres and builders' merchants.

Step-by-step installation

1. Set the fall: drainage works by gravity, so the pipe must slope toward the outlet. Minimum 1 cm per metre.
2. Dig trenches: 40–60 cm deep, 30 cm wide. Lay them in a herringbone pattern, 3–5 metres apart.
3. Line with geotextile to prevent silting.
4. Add 10 cm gravel on the bottom.
5. Lay the drain pipe holes facing down.
6. Backfill with gravel to 10 cm below surface level.
7. Close with geotextile and top up with soil.

Where does the water go?

Options:

• Soakaway: water slowly percolates into the ground
• Ditch or watercourse: check with your water authority
• Storm drain: not the foul sewer — check with your council

Connecting to the foul sewer is illegal and can result in a fine.

Costs

For an average 60 m² garden, expect £400–1,200 in materials. DIY is perfectly feasible but hard graft — hire a mini digger if you can get one into the garden.

Curious what your garden could look like after a complete makeover? Upload your photo on GardenWorld and get a custom design within a minute.