If it's shaded by a maple, I am surprise that it's moist. Perhaps because it's raised. How dim is the shade? How long did you give for the hosta to be established. Small hostas are very slow growing and may take a while. You mentioned slugs, what's causing the current plant to fail? Paul

Continuing with the tropical theme, bromeliads, palms, ferns, Heliconias, Vireya rhododendrons, Begonias,etc. Some of my favorite shade plants in the above categories would include Neoregelias, Vreasias, Alcantarea imperialis rubra, Chamaedorea plumosa, C. tepelijote, C. costaricana, Rhopalostylis chathamica, Howeia forsteriana, Blechnum gibbum, Cibotium glaucum, Cyathea medularis, Asparagus densiflorus 'Meyers', Asparagus retrofractus, Heliconia scheideana, H. latispatha, H. aurantiaca, Rex Begonias, Begonia 'Irene Ness', Schefflera pueckleri variegata, to name a few. For nearly year round flowers, things like Abutilons, Iochromas, Fuchsia boliviana, Clivia miniata and C. nobilis, Neomarica caerulea, and colorful foliage plants such as Iresine herbstii, Stromanthe sanguinea, Clerodendrum quadroliculare 'Brandonii', Aucuba japonica variegata are also nice and easy. For clumping bamboos, Drepanostachyum falcatum 'Teague's Blue', Chusquea coronalis, Otatea acuminata 'Aztectorum', Phyllostachys nigra, and Sasa palmata var nebulosa are personal favorites, with the running ones in containers.

Well, because the roots of the black walnut tree emit chemicals that inhibit the growth of other plant with in its canopy and to a lesser extent the oak trees you have very limited choices. I don't have any suggestions but you can google the conditions and see what you get.

You haven't said whether there is anything there at present, so I am assuming not. As you are planting in a long narrow strip, you will need some shrubs for the "back bone" of your garden--somethings that will provide some interest while your perennials are growing and before they bloom. I also imagine that this is a side of your home--generally side plantings require some height to offset the long and narrow aspect of the space. A mix of evergreen and deciduous shrubs is also desireable so that you continue to have some interest in winter. You don't have to do this all at once, but you should consider purchasing a few shrubs each year. Look for an upright/columnar evergreen, maybe some boxwood, hydranga should do well with this exposure, as long as it is well watered, and will give you blooms as well. There are also some roses that will do ok with this amount of sun. Rose of Sharon (not a rose) is a lovely arching shrub with beautiful blooms; magnolia is another possibility. For perennials, look at coneflower, monarda, as well as those listed above.