i'm putting a 4 inch wall about 5 bricks high in my garden to hold soil as a plant bed. do i need to bother with foundations? thank you x

I would definatley use a foundation of some sort just to make an inverted T under the soil, this will stop the weight of soil pushing the wall over... a course of 4" concrete blocks will do the job nicely

always foundations, for garden walls the width is more important than depth. minimum 100mm concrete, with the foundation 3x the brick width. so 100mm single skin needs 300mm wide concrete