I have grown annual phlox and loved them but cant imagine them being useful as a filler for a large space. They seemed kind of demanding of an exact location and soil. If you get plenty of sun here I would try California poppies and maybe orange cosmos and even nasturtiums. These are annuals I have had great success with direct sowing and they require very little care once you get them going.

I have that same type of clay soil and to get seeds growing in it is sometimes difficult especially in full sun. If the mulching trick suggestion doesn't work you can always ammend your soil with maybe some topsoil or even potting soil. What I have to do is actually grow my plants in my make shift growing area that I incorporated from a few winter sowers. It consist of a pan and water bottles I cut my water bottles in half and on the bottom for vents and add soil and seeds I water by just putting water in the pan. Granted it is not direct sowing but I seem to have my best luck with either growing my seeds this way or in my afternoon shade beds then transplanting. Trying to keep up with watering a seedling in full sun is not fun and they need the moisture or they will not grow. By the way I think from your first frost date you should have plenty of time to grow and collect seeds from your plant before your frost hits.

It's not too late to direct sow annual poppies - you could do it any time now until well into March/earliest Spring.

@floral_uk z.8/9 SW UK Perhaps I am. Indeed, I know I am overcomplicating this. Apologies. I guess? While I appreciate your offer of help (or maybe, more precisely, the claim that you are offering help). . . let me just say that I feel as though, from your tone--you decidedly do not understand what it means to be on a fixed income and rent (e.g., not have any long-term commitment to the garden you're trying to improve). I don't have time; that's exactly it. Annuals just make more sense. It's unfortunate that I have some shade, but I have to make the most of it and figure out what works for me. I can't spend $400 on plants; I don't think I can spend $200 on plants, frankly. And then all the other stuff @floral_uk z.8/9 SW UK: e.g., Hall's Honeysuckle might seem to you to be ugly and "potentially invasive,"--admittedly, it is in most places--but it decidedly is not in Portland, Oregon, from every single source I've read. And trust me, I'm thorough. I just want something that will thrive and grow quickly despite my difficult soil conditions. That's why answers like those of @einportlandor are a little more helpful, you know? "Yeah, I was broke, too, I understand how you feel... planted poppies and nasturtium and it all worked out fine!" This isn't rocket science. I just want my backyard to look nice. On the super-cheap. I don't need cutting comments for no good reason guised as "help." And to address your query re the soil; argh. I have done everything within my very limited means and power to fix the soil problems and spent approximately $700 in the past year in the wrong-headed attempt to do so: I mixed in 6" of compost 2x by double digging and excavated about 50 gallons of pebbles/rocks and a miscellany of items left by previous tenants. I created a swale and taught myself how to build a rain garden to handle what the gutters can't manage; I regraded the yard, aerated the lawn; etc. etc. This year, I decided to give up on anything more than a little patch o' grass for my dog and constructed "lasagne"-like raised beds (not supported by anything; my landlord won't let me install anything permanent, like even a floating deck, but I put down wood chips everywhere else. It's the only way that I'll anything approaching meaningful drainage (on my budget) and not spoil even moisture-friendly perennials. Forgive me; just a bit frustrated by what feeling like I've been subjected to [inexplicable] derision/passive-aggression rather than been helped. I'll back out slowly now . . . I honestly don't believe you really even want to look at photos or mappings of my garden (other than to get in something that might be helpful but will definitely be officious). I don't ever do this but this nice/mean thing sucks and I just had to respond; sorry. Thanks all.