Hello and welcome. We are in the main a UK based gardening forum so probably will not be able to give you any help. Perhaps try one closer to home? Sorry! The structure looks lovely by the way!
Fact of nature I'm afraid. No grow seed will help the germination problems if any.
Just coming into flower now.
It grows like a weed in my garden. Seeds itself. I grow it beside my pond in full sun and gravel.
Who needs photos!
Do you mean white flowers?
Have you tried digging st various points along the fence. It could be that the builders have been a bit over generous with the concrete for the posts. I would have another go and even try digging out the rubble. In the ground is much better than pots.
The daisy one could be giant scabious. Is it pale yellow?
Aluminium does get pitted over time and nothing you can do about it. Common or garden dirt will come off with a scrubbing brush and hot soapy water. I would put a splash of jeyes fluid in it as well.
I think it's Roxie.