Since it's a rental and conditions in the ground may be tough, stick with the pots. Impatiens are an obvious choice, but there is a galaxy of other shade tolerant plants you could try. If the nurseries you have gone to don't have 'Shade' sections, maybe you have other places you can shop where they do--or have salespeople who can steer you to some candidates.

Frivolous, that's rough. I feel for you. Impatiens do great in hanging baskets, by the way. I have more shade than I would like and those impatiens baskets are a colorful Godsend.

There are some very pretty coleus. They aren't all green leaves, so you might want to check on them.

I'm no expert on flowers, but I know there are some irises that do very well indeed in wet conditions. I don't see why you couldn't put them in pots if you think you'll be in your current location for a while.

How about some rhodies and azaleas? Plant 'em high.

Tulips, grape hyacinths, etc. do well in pots, and the upside is after they die back, you can plant around them. They will take as much sun as you can give them though. Pansies are so hardy and they will take lots of abuse. So colorful and pretty. Terrific in pots. They do pretty well in shade.

If you go back to that garden center, you might ask the person on duty about native plants that would do well under your conditions. Perhaps there is a native plant society in your area?

Do keep in mind the hanging baskets. If there is any spot that gets even a little sun, (a fence, garden wall, even some area under a tree that gets some sun, you can hang a basket.)

Good luck.

Mary