1. Ohio is decidedly colder than New Jersey!

2. consider this, put two identical plants in two pots. One is 6" by 4" deep the other os 6" by 6" deep. which will have less extremes? most likely the larger pot. Less drying and slightly less temperature changes over short periods. The depth of the bog only stabilizes the moisture and temperatures. Is a bog that is 10" deep more likely to dry out than one that is 18"? probably. Remember Freezing solid depends on how solid freezing is. Some plants, as I've said before can take more cold than others. I've seen iris in zone 3 with their roots at or near surface...that's frozen!

3. Go 10" if that is what you can do, I suggest 18", more than that for a bog is a waste of time and is back breaking work.

4. I do not recommend dirt. It can add nutrients and impurities that will not be good for a bog (I know I made a similar mistake with crushed oyster shell). I use peat, sand and pine needles. Quit worrying about insulation! If a plant is rated for your zone it'll be fine in your bog, cripe I have plants rated zone 7 that have been thriving in my bog for years and I'm zone 5 borderline 6.

Fred,

Thank you very much for the info. So, then I will make my entire bog surrounding my 32x20 pond to be 18", and ignore the seemingly pointless advice that some sites say in recommending 2.5 feet depth - maybe they are talking about some sort of enormous bog plant that i wont be having. Since all those plants survive year after year in your bog, they will, i assume, survive the winter also in mine.

in zone 6b or 5, would 14" be risky in winter?