Waterlogged lawns are common where the soil is compacted clay. However, waterlogging is becoming more of a problem as the UK experiences long dry periods followed by deluges. The soil is baked hard and the rainwater has nowhere to go, so it lies on the surface, turning your lawn into a swamp and drowning the lawn roots.
If you notice your lawn feels squelchy underfoot, don't walk on it. Walking on the surface of a waterlogged lawn will damage the roots, leave indented footprints and hasten the demise of the tender grass growth. Wait until the lawn has dried out before attempting treatment.
When the standing water has gone, aerate the lawn with a garden fork or aerator. A hollow tiner is the best thing to use, as it removes tiny plugs of soil. If your flooded lawn is a very rare occurrence, then this may be all the treatment necessary. Aerate twice a year to prevent further waterlogging. Filling the holes with horticultural sand will also help.
Keeping lawns nourished by regular feeding helps them to recover from stress caused by flooding or drought. Apply fertiliser in spring and phosphorous-rich lawn feed in autumn. The best time to feed is right after aeration.
It is possible to install a drainage system by laying a system of pipes leading to a soakaway at the lowest point of the lawn. You will need to identify where the water is running off, dig a hole at least 1m square by 2m deep and fill it with rubble topped with 15cm of gravel. Lightweight slit plastic pipes are available, specifically for drainage purposes. Lay one main pipe at least 40cm deep, on a bed of gravel, ensuring that it slopes slightly towards the soakaway. Depending on the size of the lawn, install additional smaller pipes. They are laid closer to the surface, sloping towards the main drainage pipe, in the direction of the soakaway.
If all else fails
Consider re-laying the lawn if standing water has destroyed the root system. Remove the top level of old grass and soil. Spread a 5cm layer of sharp sand before turfing on fresh topsoil.