What to fill the raised bed
I am planning on building a 4' x 8' X 20" raised bed with untreated pine. Once I build that, I would like to know what to fill that with apart from the soil? Gravel or cardboards or mulch etc., Do I need to layer the bottom with mulch? I thought of landscape fabric, but I read here in the forums not to use it. Do I need to remove the sod? I am not planning on using the garden soil, hence I am building 20" height raised bed. Basically how do I layer the raised bed is the question.
Thanks in advance...