Onion sets can be purchased at most garden centers,farm type stores like Agway,places like that. Broccoli had be purchases as seeds which you can start inside,if you have lights,and then put out or you can buy the plants in the spring when it's the correct time for planting.Not sure what you mean by garden boxes though. I plant my onion sets when I plant my lettuce which is usually around April 15,sometimes later. I plant broccoli in early May because all it takes is a couple of good freezes and they're history.

I have raised garden boxes because I live near a creek and my first year the garden flooded and most of the vegies rotted. I had great success with the raised beds last year. But I got a late start on lettuce, onions broc ect and didn't get a good crop. I was just curious what the ear;iest I can start.

Right now I still have parsley, rosemary, and some onions that are still editable do to the mild winter we are having.

I am going to start strawberries and asperagus this year as well any pointers?