If hosta struggles your options are limited. Perhaps some judicious pruning to open things up would be a good thing. Otherwise, what's your opinion of moss?

groundcover?..ivy..periwinkle..euonymous

Lily, considering the trees are 30-40ft tall, not too likely. :-) As far as moss goes, there is plenty of that where the grass couldn't handle it. Had wondered if any of the hardy ferns might do well.

I do wonder if it might be an issue of too shady AND too moist. My dad is going to try cutting back on the water that bed receives and see if it makes a difference.

maybe hellebores?..I have some in shade..

All of the above are good choices. No flowers but Ostrich Ferns will grow most anywhere, and dare I say it- Lily of the Valley. I would also check out some native shade plants for your area; they would be well adapted to growing in those conditions. Good luck.

@Debbiecz3: LOL. Deb, would you believe I once did try LotV at my folks place and it died? Heh. I had planted some pips at the base of a mature silver maple. My suspicion is that the LotV was unable to compete adequately for water. (For those unfamiliar with silver maples -- Acer saccharinum, they grow a very extensive shallow root system.)

Hmm, rarely see Epimedium around here. Also, couple plant sites where I saw it offered list them as "light shade". Anyone growing them in heavy shade?

Paul, I’m including two photos of my garden under a limbed up blue spruce. There are Several epimedium growing near the base of the tree. Another photo shows under the same tree I have yellow loosestrife blooming at the base of the same tree. I didn’t think it would bloom here, the shade keeps it in check. I was desperate to find a plant that would grow in the spot and figured, what the heck, I’ll give it a try.

Paul I have the Epimedium and Polygonatum growing between a huge Acer saccharinum and a very large Juglans cinerea. That is a tough combo to grow under.

Is the Purple Loosestrife the only one that is illegal in several States, (Illinois,

Michigan, etc.) and not the Yellow, too?

Sounds like a good spot for Hakonechloa!

Astilbe will love the extra moisture. Mine are happier in total shade than they are in sun, but we have dry summers.

brunnera and Solomon’s seal are a few more that may do well.

Purple Loosestrife and Yellow Loosestrife are actually from two separate families. Purple Loosestrife is Lythrum salicaria, where Yellow Loosestrife is from the Lysimachia genus. As far as I know, Lysimachia vulgaris can be aggressive/spreading but isn't illegal. There are other varieties of Lysimachia, though, that are native to the US, though I can't say I'm familiar enough with any of them to say much more than that.

I kill Astilbe by dehydrating them, so they might enjoy your moister conditions.

Heuchera are pretty shade tolerant, as well, and come in many colors of foliage.

This is the north side of my garage in late afternoon, and this is the most sun they get all day. No gutters so they get drenched, this bed rarely dries out. My astilbe and Jacob's ladder do pretty well there.

I live in sunny Atlanta, so I can't be much help. I'm chiming in because I have epimedium in a pot in heavy shade. It's at least 20 years old. My epimedium is grown under the shade of a mature Lady Banks rose. I can't say I love it but it thrives, so I leave it.

I love my variegated Solomon's Seal, but I get a little bit of sun everywhere I grow it.

I would grow hellebores or fern under those trees, but, again, I live in Atlanta. I have tried polygonatum and absolutely hated it. I have also had ivy and wouldn't wish that on my worst enemy. I'm still trying to kill that one. Have heuchera now and much prefer heucherella or tiarella, but, again, am in Atlanta. I have a lot of shade. Good luck to your father, whatever he, and you, decide.