who ever came up with the idea that you can grow three tomato plants in a 20l growbag needs shooting imho. and cucumbers for that matter.
i dont grow carrots in rows, i grow them in clumps, ready for pulling as bunches and i dont thin them, just grab a handful as needed, its always worked for me, and doesnt attract fly.
i grow beetroot the same.
i dotn thin parsnips either and dont sow till may,