Some years ago a neighbour diagonally behind our back lawn removed a tree and small shed to replace them with a bigger shed, but repositioned. It has left a small space that in the winter and spring allows a clear view down to our patio, should the neighbour want to look. In the summer, however, our ash, hazel and other trees behind our lawn successfully screen the gap. There is a sort of wooden fence there which I've modified with a trellis so that a holly tree's branches can be woven in to provide a bit of a screen. However the layout of the area would make it awkward to put a new and higher fence in. The local garden centre is selling Thuya Plicanta trees at a decent price (£19). One of these popped in the ground near my last ash tree would solve the problem. However the area is full shade. Would the Thuya grow?
Thuja plicata will grow almost anywhere, but will absorb any remaining water and light in that area. I'd go for another broadleaf tree if possible.
I'd be expecting a pretty massive plant for £19! - I buy 50cm Thuja plicata for around a quid. Personally if I was planting in the shade I would be buying a large plant, as its going to grow more slowly in shade, so a larger plant would fill the gap sooner, although you could, for example, put up a fence panel and plant the tree in front of it for instant privacy, and then let the plant grow over time. You could get some nicer looking conifers than a bog standard Thuja plicata, but the points that HarmonyArb made would still be the case.
I should have added, it's an AUREA type of thuya, and has golden-green foliage (which would look rather nice against the darkness of the background)--perhaps lack of sun would turn the colour to ordinary green? (yes, Kristen, they are about 3 ft tall at the garden centre)
Aurea is an attractive variety. Dunno about the colour if it is in the shade though, sometimes shade enhances variegations (that get bleached out in bright sun). Its going to grow nearly a foot a year, although probably won't do much in the first year, so a 3-footer sounds OK