Leeks and onions do fine this way. For me 1.5" of bottom grows back usually within a month depending on the season.
Bob

Another gardenwebber posted about his experiance with planting green onions from the store.

~Rose

Here is a link that might be useful: Planting grocery store green onions

The green onion roots I planted from grocery onions are doing better than the onion transplants I put in the ground at the same time.

I planted my store bought red onion that had some shoots. Now it has long green shoots and one is longer with an onion shaped tiny top. IS that a flower? Will it indicate when a new onion will form as 2 "daughter" plants have sprouted beside the mother onion, I planted. Wondering what is growing..jsut scallions or onions to harvest later? Anyone know? thanks.