I would not attach to the downspout itself. Attach to rebar sunk well into the ground (depth depends on soil texture, but in my soil, a foot or so works well) or attached to the side of the building if that suits your siding. I usually use the rebar since it is easy to work around when doing maintenance on my wood-sided buildings.

Thanks Babs! Will use the rebar - we have brick and aluminum siding and I don't want to attach to that. Now if the weather would warm back up that would be great!

Brick can have things attached with adhesive if you end up deciding that might work better. Avoiding attaching to the aluminum siding is a good call.

Babs or anyone :) Have you used these? Wall trellis I was thinking about getting them to use above/ to the side of a couple of trellis to train clematis around a window. Not sure if they would be sturdy enough for roses, but may give it a shot.

I have not, but I have seen reviews by others who used the similar (or identical?) kit from Lee Valley Tools. Here's a thread with a bunch of comments.