I had some onions sitting on the counter for a long time and one of them sprouted, so I planted it in a flower plot to see what would happen. At first it grew well, sprouting several long green fronds. In the last week, however, it has declined, the tips of the leaves turning yellow, then withering. Some of the fronds have started to wilt even though I keep the soil watered.
What can I do to keep the onion alive?