Installing drainage before topsoil

Do you need it?

Dig a hole about 30 cm (1 ft) deep, fill it with water, let it drain, then fill it again and time it. If the second filling takes more than a day to drain, or the ground stays squelchy for days after rain, grass roots will sit in water and the lawn will be thin, mossy and prone to disease.

The options

• Improve the soil: on mildly heavy ground, breaking up compaction and working in coarse sand and organic matter is often enough.
• A French drain: a gravel-filled trench with a perforated pipe that carries water to a lower point, a soakaway or a legal outfall.
• A herringbone system: several branch drains feeding a main drain, for large, persistently wet areas.

Drains need somewhere to discharge. Check local rules before connecting to any sewer or watercourse.

Why now

Trenching is easy on bare ground and destructive on a finished lawn. Lay drains after the coarse grading and before the topsoil goes on, and keep a record of where the pipes run.

Next: terrace any slope steep enough to wash out, then clear and cultivate the ground.