Posted: 24/02/2014 at 21:42
My garden had ponds that are at the level of the water table. This means some areas can be under water at times and totally dried out at others. Plants that seem to survive are the comphreys, Symphytum officinale is the native one. Marsh marigold, Caltha palustris, though that struggles a bit if it's hot and dry. Meadow sweet, Filipendula ulmaria. Pendulous sedge, Carex pendula. Cuckoo flower, Cardamine pratensis. Flag iris, Iris pseudocorus. Figwort, Scrofularia nodosa
Areas that vary between standing water and completely dried out are very difficult to get looking good towards the end of a dry summer.
Making up some of the area with rubble and some soil would extend your choice of species