In spring 2014, I purchased bunching onion seeds from the grocery store I believed and planted in the garden. My husband and I rented a duplex and the landlord allowed me to garden. I planted the seeds behind the garage. Only one plant grew.
As we moved out in fall that year to our house, I dug the onion and replanted in my garden. I left it in the ground year round. It is a variety of Japanese bunching onion. It grows big stalks and multiplies underground into 2-3 plants. It looks more like leeks. I cooked few times with the stalks but I don’t dig the bulbs out. I only cut the stalks for cooking. I divided the plant few times. It produces seeds in summer. I let the flower heads fall back on the ground or I spread the seeds in the garden but they don’t grow I can tell They might probably got lost in the mulch. I would try to harvest the seeds and start indoor.
They are many variety of bunching onion. Some are hardier than others. Make sure you buy a variety hardy to your zone. Mine is hardy to my zone 5.
You can find other varieties at Baker Creek Heirloom Seeds.
They are a nice addition to the perennial garden as they are maintenance free and I don’t water them at all. They come back every year and they don’t die back in summer like Egyptian onion, shallot, or yellow potato onion. They stay green from spring to early winter.