Given that it is in the garden, I would want to go mortarless if possible and just stack the brick. It might be more stable to use retaining block.
You could do one course of brick alongside each other lengthwise, then the next course with the brick going perpendicular. I have a wall like this which has been standing for 7 years and the brick were fairly irregular old terra cotta type brick. The wall must be 4' tall.
I would just put in a trench maybe 18" deep and as wide as a compactor and compact some 3/4" minus stone in there and stack on that.
How is the drainage in the area you want this?
You could do one course of brick alongside each other lengthwise, then the next course with the brick going perpendicular. I have a wall like this which has been standing for 7 years and the brick were fairly irregular old terra cotta type brick. The wall must be 4' tall.
I would just put in a trench maybe 18" deep and as wide as a compactor and compact some 3/4" minus stone in there and stack on that.
How is the drainage in the area you want this?