I am in the southeast and despite putting down gypsum, overseeding and aerating, I can't get grass to grow in much of my yard. I have stopped watering this area all together because it stays really wet all the time - even in the 100 degree heat with no rain. The soil is very dense clay, it almost looks black. And there is all kinds of fungus or moldy looking stuff on it. White stuff and furry stuff, not sure what it is. We also have about 15 oak trees back there so it doesn't get much sun. New soil is cost prohibitive at this point. Is there ANYTHING that will grow in wet clay? And what do I do about all the moldy looking stuff?
Typically when you are dealing with black/grey clays it is indicative of persistent water logging. This means that without a way to drain the area you may not have any success. I would consider drilling a few small holes and seeing where the water fills up to naturally. This will give you more information on what you are dealing with.
From there, you could dig in a few french drains or some equivelant to drain the water away from the area. Alternatively, embrace the wetness and plant more swampy species.
I have similar issues with an area of my farm that seems to have a rising spring. The soil under surface is more of a grey/brown which indicates that it might not have always had water logging, or at least less than if it were blacker clay. My suspicion is that a dam uphill from our property is creating the issue, or adds enough water volume to make the issues visable on the surface. Long story short, consider all factors. If you have a massive waterbody or underground aquifer nearby, it may not be possible to drain away the water.
I'm not sure about in clay specifically, but you might try reeds, rushes, Job's tears, mint, irish moss, cranberries, wild rice, stinging nettle, some kinds of bamboo, wild irises (not the domestic ones), watercress, water chestnuts, asparagus, and stuff like that.
Here's a link that supports some of those.
Weeds XD. Jokes aside Aster (Symphyotrichum) Bearded Iris (Iris germanica) Bee Balm (Monarda) Butterfly Bush (Buddleia davidii) Daylily (Hemerocallis) Echinacea (Echinacea purpurea) Sedum (Sedum) all excellent plants in clay soil As for grass "Tall Fescue" grows best. But if you're looking to break it up. Break up your clay soil by digging/mixing a foot down then add in a mix of sand. Clay soil has poor drainage, so plants that love water are ideal. Soil amendments add volume and drainage, namely sand, gypsum and compost.