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Poor drainage and waterlogging

In heavy, compacted or low-lying ground, and in pots without holes, water fills the spaces roots need for air. Plants that need sharp drainage, such as lavender, rosemary and blueberries in the wrong soil, decline and die over a wet winter.

Water & drainage
Yellowing plants collapsing in waterlogged soil
Yellowing plants collapsing in waterlogged soil

What it looks like

Damage builds over weeks of wet, and shows most after winter.

  • Water still stands on the surface hours after rain.
    Puddles that linger Water still stands on the surface hours after rain.
  • Leaves pale and growth stops, often across a whole bed at once.
    Yellow, stalled growth Leaves pale and growth stops, often across a whole bed at once.
  • Stems blacken and soften at soil level; woody herbs die back from the centre.
    Rot at the base Stems blacken and soften at soil level; woody herbs die back from the centre.
  • Dug soil is grey-blue and smells sour where it has been starved of air.
    Grey, smelly soil Dug soil is grey-blue and smells sour where it has been starved of air.

How to confirm it

A simple hole test gives the answer.

  1. Dig a test hole

    Dig a hole 30 cm (1 ft) deep, fill it with water, let it drain, then fill again. If water remains after a day, drainage is poor.

  2. Look for a pan

    Compacted layers show as a hard band a spade's depth down that roots do not cross.

  3. Check the pot

    Tip up containers: blocked or missing holes, or a saucer full of water, keep compost saturated.

What to do

Get water away from the roots, then change the ground.

  1. Lift or move plants

    Move container plants into pots with holes, raised on feet. Lift and replant small plants in a better spot.

  2. Break up compaction

    Fork through compacted soil when it is dry enough not to smear, and stay off wet beds.

  3. Raise the bed

    Grow sharp-drainage plants in raised beds or on mounds with added grit.

  4. Add organic matter

    Dig in or mulch with compost each year; it opens up clay over time.

Prevent it next time

  • Choose plants that suit wet ground, or raise the planting.
  • Never plant into a hole dug in clay and filled with compost: it becomes a sump.
  • Keep off wet soil, and use paths or boards in beds.
  • Use gritty compost for herbs and succulents in pots.

What not to do

Do not add sand in small amounts to clay; it makes a denser mix. Use organic matter and grit, or raise the bed.

In the growing guides

Where the guides mention it, with plant-specific advice.

Sources

  1. Waterlogging and flooding, Royal Horticultural Society
  2. Gardening on wet soils, Royal Horticultural Society