Garden gnomes? ivy? Not an easy place to grow anything.

It has taken me many years to overcome this problem as my garden has a canopy of 12 protected conifers. Fiirst of all I would suggest using raised beds with sleepers, wood ,rocks, edgings etc to improve the soil. Go for a mixture of shrubs and shade loving perennials. Some of my most successful plants are : Shrubs - Aucuba, Bamboo,Kerria, Viburnham, Pittosporum, Mahonia, Azalia, Clematis, Honeysuckle, Fatsia, Hardy fuschias
Perennials - Paeony, Loosestrife, Bergenia, Euphorbia, Geranium, Campion,Primroses, Grape Hyacynths, Ornamental grasses, Heuchera,
Herbs : Cologne mint, chocolate mint, lavender mint, Peppermint, Alchemilla, St Johns Wort, Chives.
Hope that this gives you a few ideas.