We have a dry shady area, which we originally planted only ferns and hostas. Because it is dry I water the centre of the plants in the summer. Slugs aren't a problem because the rest of the ground is dry. We have since added some other plants trying to keep to a colour scheme of blues mauves and whites which work well trogether in a shady inviroment. These include phlox, campaunla, perennials and rockery, clyclamins, huechera's, wild bluebells, alliums, busy lizzies in the summer and daffodils white shades. If you are only looking a low growing plants. I would suggest the smaller varieties of hosta, some of the saxifragas and rockery phlox. Dodecatheon, jeffersonia, tiarella,Omphalodes Chiastophyllum,.Miniture bulbs which will probably bloom very well if the are not too shady in the spring. Unless of course your trees are evergreen.