PR isn't great in deep shade, but no grass is. Red fescue might be the best but, again, no grass does well in deep shade. Particularly under a tree, which is also pulling in as much water as it can.

Your best bet might be to mulch under the tree.

Now that will do well in shade. :-) Other shade ground covers can be added as well for some variety if you like, and perennial plants like bleeding heart and the like might add more welcome color for you as well.

I planted a few others like lily of the valley & ajuga. I was really surprised though how well the rye is doing. if you remember morpheuspa i'm always planting bee friendly plants. this patch of rye happens to be right next to some hives.

If you don't stress it or ask a lot and don't demand that it be a lawn, it can do a pretty good job. If you can allow it to grow longer, clumpier, and more like loriope than what most people think of grass, it may very well manage better in shade than expected. Or...not, but it's going to do better than lawn-cut grass would, which would be to die the first July.

Rye can be very pretty when allowed to grow nearer its full potential height (2' or so tops), and it'll drop roots down much deeper when you do that.

Ajuga would be a good companion plant there as well, and if your ajuga acted like my old ajuga, you certainly have plenty of daughters...

ajuga grows like wild strawberries. puts out a shoot that drops a root. if it ever quits raining i'll snap a photo of the rye grass. it looks happy.

I was at the feed store yesterday & talked about grasses with the owner. he says that perennial rye will only last 3-4 years & will die out. i'm not concerned since i'm using it for temporary erosion control but find this curious.

now I have to trap molezilla. I get an occasional mole but this critter is leaving 12" mounds in his wake. I've trapped & killed 3 in other areas of the yard but so far this one has eluded me. these moles contribute to the erosion problem as well. my yard has just enough fall to it that when water runs into tunnels that run north & south when it exits on the lower end the tunnels can be 6" in diameter.

All the perennial rye that I've tried in part shade all dies out within a year. And almost always gets hit with disease. I'd try tall fescue.

As far as mole traps, look up Trapline traps. Can be kind of a pain to use in that you have to put them in the tunnel, but the trigger mechanism is more sensitive than above surface traps. Highly recommended.

i'll check out that trap. I have good luck with victor out of sight traps. sometimes you think you have a herd of moles & it's only one. in the last 2 weeks I've caught 7 including mozilla. that little bugger was making 10" mounds & of course it was in a new patch of fescue that was just getting established.

It sounds like this is an area for mulch and shade plants. Woods Poppies have yellow flowers most of the summer and are an attractive addition to the area, Hosta are always nice as a host of othernative woods plants.

There are some area that grass will not grow, You have basically two choices. Let it do what every it wants, or make it into a natural area. Letting it do what it wants means the area will always be an eye sore and a problem area. Mulching with natural and native plantings will make it an attractive focal point in your yard.

as I've mentioned the rye was meant to be for temporary erosion control. I have planted a variety of ground covers. i'm hoping the creeping loriope & lily of the valley prevail as they have tenacious root systems.