Waterlogging

What you are looking at

Water lies on the surface after rain and takes hours or days to go. The soil is heavy and sticky when wet and sets like concrete when dry. Dig into it and it is grey or blue-grey rather than brown, and it smells sour.

The plants growing in it yellow, drop their leaves, and wilt. The wilting is the part that confuses people, because it looks like drought and happens on soil that is soaking.

Losses tend to arrive in winter rather than summer. A lavender that came through August is dead in February, and a young tree planted in November never comes into leaf.

Roots suffocate rather than drown

Roots need oxygen. They respire, exactly as leaves and animals do, and they take that oxygen from the air spaces between soil particles.

Water fills those spaces. In a normal soil it drains through and air follows it down. In a waterlogged one it stays, the oxygen in it is used up within a day or two, and the roots begin to die.

Dead roots cannot take up water. That is why a waterlogged plant wilts: the soil is saturated and the plant is unable to drink from it. It is also why feeding a yellowing plant on wet ground achieves nothing, since the nitrogen is there and the roots cannot fetch it.

Then the secondary damage arrives. Phytophthora and the other water moulds thrive in saturated soil, and they finish off roots that were already failing. By the time anybody investigates, the plant has root rot and the underlying cause has been forgotten.

What to do about it

Dig a hole 60 cm deep in the worst spot in winter and see how long water stands in it. That tells you whether you have a drainage problem or a wet fortnight.

Watch where water arrives during heavy rain. A downpipe, a path or a hollow is often the whole explanation and is fixable in an afternoon.

Stay off the soil when it is wet, and use boards where you must cross.

Mulch with compost and well-rotted manure every year and let the worms work it in. On clay this is the long answer and it does work.

Break through a compacted pan once, then stop digging and mulch instead.

Aerate a wet lawn in autumn and brush sharp sand into the holes.

Plant on mounds or in raised beds rather than in dug holes, and never backfill a hole in clay with compost.

Choose plants for wet ground where the ground is wet. Dogwood, willow, alder, birch, astilbe, hosta, iris and primula are a good garden by any standard.

Give a drowned plant time, shade and no feed, and cut some top growth back to match the roots it has left.

What it gets mistaken for

Drought produces identical wilting on soil that is dry, which one finger settles.

Root rot is the usual consequence rather than a separate diagnosis, and treating the rot without fixing the drainage repeats the loss.

Nitrogen shortage yellows older leaves on a plant growing in reasonable soil, and it responds to a feed within a fortnight.

Honey fungus kills from the base with white sheets under the bark and black bootlaces in the soil, and it is often blamed for deaths that were drowning.

Frost damage on a plant in wet ground can look like winter wet, and the difference is that frost damage is confined to the growth exposed on the night it happened.