Interactive lesson

Draining wet ground, step by step

Interactive lesson: find out where the water comes from, try the fixes that need no digging, measure the fall, dig a ditch and a French drain, and lead the water to a safe outlet.

Free sample Chapters 1 and 2 (8 steps) are free. The full lesson comes with the Draining wet ground module. Already bought? Unlock

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The whole lesson as text

1. Where the water comes from

Find the cause before you pick up a spade: the fix for one doesn't help with another.

Water off the slope — It's wet at the foot of and along the slope, and after rain water runs across. The fix is a cut-off ditch above and a shallow drain along the edge.
Water on a compacted layer — The top 20–40 cm is wet, while below it's dry and hard. Deep loosening, raised beds and organic matter help.
High water table — Flat land by a river, wet with or without rain. It needs drains with an outlet lower down, ridges, or plants that tolerate the wet.
Plants that tell you — Soft rush, sedges and creeping buttercup: water stands for long periods. Willow, alder and poplar seeding themselves: a high water table.

Why: Many people dig and feed wet ground for years, but the problem isn't food: the roots are short of air because the water has nowhere to go. Water can come off a slope, sit on a compacted layer or rise from below, and often it's a mix.

Horsetail, sorrel and moss tell you: damp and acid.
Heavy clay lets water through slowly: it stands for hours after rain, then the soil bakes into brick.

2. A test pit

The best diagnostic tool is a pit, dug at the right time.

A pit 60–80 cm deep — Dig it (2–2½ ft) a day or two after heavy rain in spring, on the wet spot.
Where the water comes in — If it seeps from the side at a particular depth, it's a layer or slope water. If the pit fills from below, it's ground water.
Level and colour — Note in cm below the surface the depth at which the water settles after 24 hours. Grey-blue mottling and rusty spots mean water stands there for long periods.
Hard layer and roots — The rod test shows the depth of compaction. Where roots stop abruptly or turn sideways, that's where the problem is.

Why: A pit after rain shows where the water comes in, at what depth it stands and where the compacted layer is. Without it, it's easy to put a drain in clay when the real problem is a rotavator pan.

Enter everything in the wet-ground diagnosis, separately for each wet spot.
Do a percolation test next to the pit as well.