Q.How do I care for store-bought onions?
I purchased a white onion from the store, and it started to grow roots and leaves, so I planted it today in dirt. Is there anything special I need to do since it is store-bought, and when do they start producing seeds?
It would be best to purchase onion sets from a garden center or nursery.
A store bought onion from the produce section is likely treated for storage and would be unsuitable for planting.
Here is a link about growing onions from onion sets.
https://www.gardeningknowhow.com/edible/vegetables/onion/find-how-to-grow-onions-in-your-garden.htm