I have inherited some beds with wood edging and would add to all of the above very valid comments about slugs and weeds that on my fairly light soil they dry out far faster than the unedged beds.
I have made my unedged beds much deeper (about 6 inches) than Charles recomends and they still did not suffer from drying out as much as the wooden edged ones. Also to keep grass at bay I have put a deep edging around all of my beds that does require maintaining but having a clearly definde line it tends to get weeded with all of the rest of it and it is obvious when grass starts to encroach.
