I guess I'm lazy, but I just put 'em directly into water, and they do fine. When the weather warms (although, to be fair, I AM in Texas, and it warms in May), I'll cut the green off, then put the white bulbs right out into the garden. I get loads that way, and no fuss at all. Last year was mild, with only a few -0C days, and they came through with flying colors, and got HUGE.
While tap water will do, I recommend using filtered/mineral/spring water because it's free from chemicals. I had a mold issue before, I still manage to plant it but the green onion leaves were not so healthy. I suggest to begin with a healthy starter bunch for a great harvest! Also, as I said in the video, water needs to be changed every 2-3 days or when the water discolours. This step prevents mold issues.
