Out of curiosity, what kind of plants are you working with? Anything rare or just good old hardy greens? I’ve been adding to my own indoor mix lately and honestly got tired of running around local nurseries. Ended up finding this site where I now buy plants online—especially the smaller stuff like succulents and low-light houseplants. Saved me some time and guesswork. Would love to know what you’ve got going! Always cool to hear what others are growing.

I'd put them in pots so you can move them to hospitable locations as the temps soar all the live-long summer. :(

I wouldn't plant right up against them. I'd spread out a layer of mulch (we use pine straw but shredded hardwood is very nice) in a circle 5-6 feet all the way around the tree. Or certainly if you can get a nice carpet of moss going, that would serve a similar purpose. Then plant further out. I think planting too close is hard on the plants, hard for you to dig and to maintain (lots of root competition), and potentially stressful for the tree (depending on how much you do). A nice layer of mulch or moss is plenty attractive and restful to the eye. If you have any deer nearby, don't bother planting hostas. Getting fern divisions from your mom sounds like a good way to start (and economical). If you want to id them (the ferns), take a picture and post it on the Name that Plant forum.

If you have enough slippage some time the plants will just go with it. Maybe you need to plant using jute erosion netting or even something like Hold A Hill blocks.