By Miriamhare
Somerset,
United Kingdom 
We have a very wet, west facing bed, with clay soil. This autumn we are going to make it into a raised bed . How can we improve the drainage in this bed and what would be good plants to plant here? The bed is twelve by seven feet.
2 Aug, 2015
As you're building a raised bed you can create the soil conditions that you want.
If you want something to be largely unaffected by the clay then you will probably want the raised bed to be at least 18 inches deep - the deeper the better!
Dig a load of grit/gravel into the existing soil then add a 2-3 inch layer of grit/gravel before placing your new so/compost.
Depending on what you're building the walls from, add drainage holes low down (in the gravel layer) to allow excess water to drain away.
Alternatively, don't build raised bed and plant things that will appreciate the extra dampness - hostas, astilbe, bog arums, Iris sibirica etc
3 Aug, 2015