Morning. I have a very similar patch to the north of my house. I have very threadbare looking grass and some fairly sickly looking bulbs coming up (crocus looks ok (if thin) and Daffodils and Narcissus look tall and thin, no sign on the anemone I planted!).

I did a rethink, just planted Jacobs Ladder and am planning on planting Hostas (loads of varieties available). Jacobs ladder has purplish flowers and Hostas flower as well - all are shade loving. You can also try some Japanese plants like Fatsia Japonica, Aucuba Japonica, Bamboo such as the Murielae and Mahonia. All these are hardy, so will do in a seaside locale. I just planted all them in he shady parts of my back yard with the bamboo in a large pot in the front one.

I did notice that my front garden does get some light, now that the sun is higher, so perhaps your garden gets more light, if not directly than you think.

Aucuba Japonica is commonly planted in parks, so you might be able to get cuttings form there - I did that but have limited success in actually getting them to root so far.

Click on S on the A-Z at the foot of the page. then on shade plants. There is lots to choose from also have a look at pots under P. If it is very windy then choose lower growing plants otherwise the pots might topple. If you have big pots Queen Elizabeth is a tall rose which is pretty sturdy, will grow in the conditions you describe and can be pruned to give a flowering pillar of sweet scented pink roses. Can youplant in the soil at all, loads of shrubs will survive there too.

Epimedium thrives in shade . . . different coloured leaves, some bronze, and pretty tiny yellow, cream or pink flowers. Hardy geraniums also love shade, blues, white and pale pink to deep pink.

Depends on how narrow your strip is. Euonymus Fortuneii will be happy, lily of the valley, heuchera, alchemilla mollis, pulmonaria (there are some lovely bright blue ones in flower right now) ompholoides, lamium will all grow in a strip only abut eighteen inches wide - I just looked out of my north facing window at what's growing there. In summer you can add some colour with fibrous rooted begonias. And if you want it to fill up all by itself with eventually no effort from you, euphorbia robbiae will do the trick.