Attaching a window box?

[cloodup]

I would like a window box for this window. I assume it is possible to get boxes that fix to the wall rather than sit on a cill, yes? However, it's a cavity wall (a converted garage in a 1930s semi) and I'm a nervous about making holes in it, or that the fixings might not be strong enough to hold the weight of a window box. Any reassurance or pointers would be welcome!

I’d measure the wall and go to garden centre. They usually have really nice iron window wall planters - like a hay rick. You put a hessian type liner in (garden centre sell these too). I would then secure an appropriate length of wood to the wall - either treated with wood preservative or painted. Then hang the wall planter from the wood using the special hooks provided with the planter. It will look very much nicer than a window box - a softer look.
Happy planting.

It might be easier and less risky regarding damp if you bought a free-standing trough.