Sounds like you're good to go! Standing water you want to avoid otherwise moist is good.

I'm struggling with how wet is too wet, too!

We have a low lot, and a raised septic system. We have a "pond"/muckhole that was scratched out of the ground and represents the level of groundwater, it's no more than 24" deep when full (on ledge). It is only dry in the droughtiest of times. And there is no shortage of frogs, toads, salamanders and mosquitos here. ;)

I've lost 3 Ligularia, Astilboides tabularis, Japanese Iris in the past year/two. I'm discouraged because I don't think I'm selecting the sorts of plants that are able/willing to accept seasonal deluges. Have I misjudged my plant selections or have I failed to offer them the sort of frost/heave protection they require?

Hope you're able to help because I KNOW I have a "boss" site if only I can zero in on the right plants. I'm nervous about more "invasive"/aggressive varieties as the area in question borders a magnificent natural fern dell, replete with all manner of native ephemerals... and I'm unwilling to jeopardize them for the sake of something "showy". (I'm thinking of Petasites japonica; love the variegated sort, but am very afraid of it "getting away"!!) I've been to Naumkeag.

Mostly partial shade/shade... the plants in the sunny area (also higher) are doing fine. Japanese Iris, Veronicastrum, hardy Hibiscus.