Robyn,

Would there be an avantage over making my 30 foot long soil bog strip to be 12" wide as opposed to 10" or even 9"?


would the extra 2-3" help in overwintering certain common marginals or would it help in the retention of water, in particular?


(only need it for iris, arrowhead, ferns, marsh-marigold, cardinal flower, forgetmenot, etc.)

Are you talking about width or depth? Extra width would just allow you more room to put in more plants and more room for them to grow. If you meant depth, more depth would help with retaining water and give you more versatility as to how much of whatever to put in there.