Posted: 03/05/2014 at 23:59
Grow bags are just bags of compost of a size where it is convenient to lay them flat, cut a hole and plant whatever in them. They can be stacked up and used two deep with suitable holes cut in them for deep-rooting plants..
They are cheap and cheerful and often have pretty rubbishy compost in them, but as you won't handle it you'll never know. The fertilizer in them will last somewhat less than MPC.