Struggling with Spinach — would appreciate advice

I want to be honest: I'm not getting great results with Spinach and I'm not entirely sure why. blight in warm wet summers especially on tomatoes has been a recurring problem despite my attempts to address it. I've been focusing on feeding with a high-potassium fertiliser once flowering begins based on everything I've read.

satisfaction of harvesting food you grew yourself is there in glimpses, which tells me the plant has potential in my conditions. I have it in a greenhouse or polytunnel for season extension which might not be ideal. peak harvest in mid to late summer showed some improvement. Two stars for now — not the plant's fault, but not a success yet. I'll update if things improve.