i can leave an extra 2-3 feet for over lap where i can dig a shallow flat 4" deep impression in the earth where i can put the liner in to line the impression -


the purpose would be to grow marginals in the 4" of water-trapping soilfilled area around the pond


will they die in the winter, i can put an extra 2" of soil on top with only stones to trap in moisture - therefore, 4 plus 2 inches of soil - is that enough for things like water mint, grasses, ivey, forgetmenot, and some bog plants?


do they need like a foot in order to over winter for their roots to go down?

If kept damp, those plants should do fine. You will just have to try some plants and see which do well and which die. Some plants do well in one person's pond and poorly in another even if they are seemingly the same. Again, there are too many variables.

robyn:

why do you think many bog sites recommend at least 18" of depth for a soil or soi/peat filled lined bog?


in zone 6b, what would the least depth you would recommend?

i was thinking either 10" or 12".

i suppose the depth effects water retention and over-wintering considerations, but not so much root growth - because im only interested in planting arrowhead, iris, pickerl plant, and a few others which dont have to go too deep[?] - so keep that in mind in your response.

thanks.

"why do you think many bog sites recommend at least 18" of depth for a soil or soi/peat filled lined bog?"

The depth allows for room for the plants to grow down and to support the height of the plants. If the bog is permanent, then that depth makes sense. Most marginals though can be supported by less depth than that.

"in zone 6b, what would the least depth you would recommend?
i was thinking either 10" or 12"."

I guess a foot.

"i suppose the depth effects water retention and over-wintering considerations, but not so much root growth - because im only interested in planting arrowhead, iris, pickerl plant, and a few others which dont have to go too deep[?] - so keep that in mind in your response."

Yes, water retention and overwintering are considerations with things being better with more depth. Also, more soil holds more nutrition as well. In small amounts of soil, it will be spent of nutrients sooner (without artificial fertilizer added). The plants you mention can grow main roots down half a foot or so but the iris will go even deeper. The smaller hairy roots may go even deeper.