Why complicate life by starting onion seeds indoors then transplanting them later into the garden? It’s much easier to start with onion sets (baby onions), widely available wherever onion seeds are sold. All you have to do is plant them in the garden, then harvest them at the end of the summer when they’re mature. Sometimes life is so simple! Using onion sets is particularly recommended if it’s your first experience growing onions or if you live in an area with cool summers.
You can plant onion sets as soon as the soil can be worked and there no more risk of severe frost (-7 ° C). Just plant them at a depth of about twice their height, spacing the small bulbs about 4 to 5 inches (10 to 12 cm) apart.
Warning: if you have had problems with leek moth (an insect that attacks onion leaves) in the past, it would be wise to cover your young onions with floating row cover after planting. Here is some information on this technique.