The ones I have in the ground right now were planted in late summer from topsets in a double row 12" apart on a 2ft wide bed. I graded the topsets and selected the larger ones, about marble size then planted them about 1" apart. Each topset produced 2-5 scallions and during the fall I thinned them by pulling up about 3/4's and left one clump of 2-3 plants every 4-5 inches.

This produced all the scallions I needed to sell for the fall season, and the quality was very good, yet stronger than your average store-boughten green onions. Good for cooking, but I eat them. I sold them in a 10-stalk bunch for $1 and almost always sold out. The remaining plants overwintered and are now beginning to produce topset buds.

Once the topsets are fully matured in midsummer, I will dig up the plants and harvest 1" bulbs at the base of each plant and sell them like shallots, then start the whole process over like last year by replanting the topsets in late summer.

Since I was unsure about the sucess I woud have with this crop last year, I withheld from sale almost half of the bottom bulbs, but ended up not using them, and they carried over fairly well during the winter in a mesh bag hung in my unheated workshop. I have some available for trade, and am seeking garlic chives in trade

I was able to carry over the smaller grade topsets through the winter in storage, and planted them a few weeks ago and will be able to sell them for scallions this summer.

So this form of allium appears to be a sustainable source of easy-to-plant and quick-to-grow scallions and "shallots" from which you can get three harvestable crops/year, and requiring no input for seed. Who could ask for more?

If I could figure a way to sell enough locally, I would venture to say these could create a foundation for an entire business.
The guy at the link below, and everybody else, it seems, charges an outrageous price for topsets.