Hi there, I'm in Catalonia too, but on the other side of the mountain! I've done a few wedding flowers in my time and your idea sounds great!! You should be able to keep asters (michaelmas daisies) and with a bit of luck and a lot of shade and water, roses should be in second or ongoing flower, but in pots.....hmmm and you're a bit late to plant them in the ground and expect them to flower this year, but ... neighbours??? You could always go the grasses and corn route plus a few hops (do they grow wild near you like they do here?) and I've generally got Perovskia in flower. You could try some cosmos too - they grow like weed here, single open flowers -v. simple and loads of feathery leaves - they cut well and look great stuffed in jamjars ,but I'd avoid the dahlia thing - they can be lovely but a bit stinky close up and earwigs down your cleavage aren't a good look, now are they? You could use eucalyptus (not suggesting you grow it in a pot though) and rosemary - also some of the sage family flower late. You must have some olive trees you can rob, sorry , prune and the good old oleander off the roadside should still work.You might get love- in- a- mist (very apt) and if the flowers have gone over the seed heads are fab. Some of the sun-flower varieties are interesting, not the ones you grow for bird feed though, some of the cultivars have multi-heads that aren't necessarily the size of dinner plates. Depending where you are, have you any neighbours with bougainvillea? Makes great traily bits (but has thorns) Of course, what you choose depends on what you want to use it for- your hair, tables, walls.... Hope some of this helps, have a great day.