Rather than throwing ashes in the bin can I use them to grow vegetables in a raised bed? The ashes are those derived from burning dry wood cuttings (raspberry canes, pruned branches etc.) How deep should the raised bed be? Can I use a base of 8 cm polystyrene sheets to build it up to a convenient height?
A raised bed is only useful if the soil is heavy and tends to need a ot of watering on normal or light soil. A height of 15 to 25cm is lots.
Layers of polysterene would restrict the roots and increase a drought problem.