How should I fill a raised bed over waterlogged soil?
MATTHEW SAYS Before you fill the bed, break up compaction in the ground below with a garden fork. Push the fork in as deep as you can and wobble it from side to side to make deep holes. Plants in raised beds need about 30cm of topsoil, but the bottom 20cm or so can be coarser material such as rubble, sand or gravel, or preferably a mix of these. The trick to good drainage is to have a range of particle sizes, so add some grit to your topsoil too.
Over time the soil will settle, so I would advise a ‘no dig’ system – simply apply a generous mulch of organic matter each autumn to cover the top layer of the raised bed. This will maintain the level of the soil and encourage a healthy soil ecosystem, which will also aid drainage in the longer term.