Hello Geek Girl,
Welcome to the site, I am intrigued you say "Of course I HAD to dig this first time – to remove the turf and loosen up the soil"
Really you don’t! and removing turf loses fertility from your plot.
Anyway that is history. I would cover now with manure to kill more turf, see No Dig Vegetable banner at top, you may have enough manure (4-6in) to need no cardboard.
Look out for Daubenton perennial kale plants, or sow May for big plants by winter eg Thousand Head.