How do I grow large brussel sprouts?

[Clkeiper]

I grew beautiful brussel sprouts last year in my high tunnel. The plants were beautiful but unfortunately the sprouts were hardly larger than marbles. What do I need to be more successful? I fertilized with a vegetable fertilizer and on occasion a watersoluable fertilizer when I watered them. I harvester 0 last fall as they were nothing. They had all winter to do something in there. I harvested someof them today as they are starting to bolt.

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