I haven't had much success with Swiss Chard in the past, in spite of it being an 'easy' vegetable. My fertilizer challenges (uh, I studied native plants, not nutrient-hungry vegetables) are evident in this regard, but I'm trying to mend my ways.
Compost, aged manure, mushroom compost, etc. as soil amendments aren't enough to maintain fertility, in continually cropped beds (eg. my main and satellite vegetable garden areas at home in the Piedmont- in the Southeastern US). So I've been mindful of the benefits of adding organic timed-release fertilizer (Espoma is one brand that provides a nice range of major and micro nutrients).
My new raised beds, in the mountains, though, have been (so far) quite supportive of leafy greens, being filled with compost and composted manure.
I've been delighted with the lush lettuce, radishes, arugula, and swiss chard that have been part of the early plantings, and have been in harvest mode recently.
This swiss chard is the nicest-looking that I've grown; it's not hugely lush, but hey, I'm quite pleased with it. And I'm sure it will taste good, too.
(But, stir-fried lettuce with sesame oil, onions, mushrooms, and garlic was on the dinner menu tonight!) And, I've warned my gardening companion that there's more lettuce to come....