I planted spinach this past fall. It never really started to grow until late winter. When it was almost big enough to harvest, it bolted.
I'm planting more kale, put in some swiss chard and I have malabar spinach sprouting. I've never tried it, but it's a vine that grows well in the heat.
Try planting it in full shade. You already are in mid/late spring, as you compare it to My zone, 5b, and I could be direct planting right now. This is the same suggestion as planting lettuce mid summer.