The "Asian" Nelumbo, Nelumbo nucifera, is a tropical plant that grows across southern and south-east Asia, across Indonesia, New Guinea and northern Australia. It's habitat is generally zone 11 and upwards. Zone 7 you're talking about freezing and they don't take well to freezing. But I don't know how far down they can go. Problem is some people grow plants they put into shelter during winter then claim they're hardy in their zone because they are growing the plants.

For some reason I thought someone here posted pics (years and years ago) with their zone 5 or 6 lotus, planted into a large dirt bottom pond, and it looked like it was thriving. Seems they had a winter pic also, with the seed heads showing.
I was pretty certain they could handle cold so long as the rhyzomes were below the freezing level?
This is the lotus also used in Asian cooking that I'm thinking about- maybe I have the wrong genus?

I don't recall seeing that particulat post, is it possible to do a search on this new format? Both the Nelumbo seed and tubers are eaten so it'll be the right one. The coldest zone I've seen them grow in was somewhere around 9b to 10a, unprotected. But I don't know if they were in a microclimate better than the surrounds. The seeds are easy to germinate if you nick them so always worth a try. I've got some seedlings now just started from the white variety of Nelumbo nucifera. They have their first couple of floating leaves. I'll be getting some seeds from the red variety soon too.

Hi

I planted,what was described as a "hybrid semi double Asian lotus "in a large pot in my 5x10 pool. It grew reluctantly through summer and went dormant. have been unable to find the tuber So assume it either died or was eaten by something.lol Just this week put some aroids if the lotus sprouts i can always eliminate them. Many years ago i grew a dwarf form that ate the entire pool lol Can't help with the cold hardiness but do recall pix of them with snow on them ?? Good luck gary

I am also from z6 and last year I started growing lotus from seed, which I ordered it from Thailand. During this winter I put my lotus in the unheated garage. Once a while I check the soil to make sure it's not frozen. I don't know if it survives till this spring. I'll post back when it's ready to put it outside.