shaded area plants

Perennial geraniums would do well there . They are tough and dont mind poor conditions. They flower in spring and early summer mostly and also many spread quickly too. I would try one of the Geranium Macrrorihzum group.

If you like ferns, try the Hart's tongue - Asplenium scolopendrium - it's very sculptural and evergreen and quite tough - as are Bergenias and any would do well. For flowers you could go for Ajuga reptans 'Catlins GIant' - also v. nice purple foliage plus Liriope muscari and Cyclamen coum.

Also, try adding lots of organic matter to the bed as it will help the area retain more water.

Get rid of your snails/slugs as a matter of urgency or you will never succeed. If you are organic then put beer traps down or buy some ducks. If you are not organic then get some slug bait and start using it soon plus beer traps.

John.

EPIMEDIUM is also a good plant for dry shade

There are lots that will thrive. in addition to the above try advice & plants try Chelone oblique [turtle head], pulmonaria, lots of blue/white/pink to choose from. I also grow telima grandiflora, heucherella, brunnera [perenial forgetme not, Jack frost is a variegated form, penstemons will also tolerate shade. any of the anemone japonica's but they get thuggish, golden rod. all of the above only get sun in the late afternoon in my garden. at this time of year the hellibores do well as do many bulbs. for late autumn height i have a 5-6ft rudbekia herbstone. exotic lily martagon will enjoy the shady parts as do tiger lilies.
hope this gives you some inspiration.

sarraceniac. you can be Organic AND use slug pellets. they do ferric phosphate slug pellets for organic gardners.