A large basal bulb of walking onion (allium cepa proliferum) planted in fall around here will develop two or three strong shoots by spring. Left undivided, these will get to medium size, make a lot of topset bulbils and make medium size basal bulbs again by the next fall. A better way to manage them is to thin the shoots down to one by using them for green onions in the spring. Then you'll get a bigger main shoot, bigger topsets and a bigger basal bulb which can be used like a shallot in late summer and can be stored for a few months. Large topsets can be planted out in late summer to make small scallions by late fall or early spring. Small topsets in mid-summer can be pickled or used for cooking.

I don't much experience with shallots, maybe someone else here is expert. As far as leeks, did you mean that you set out seedlings? I have never heard of 'sets' for leeks.

pnbrown, that is the most helpful info about walking onions I have gotten yet. I see that the bottoms can be used almost like regular onions, so it is good to know how to get the biggest possible ones. thank you

hepatica

I don't know about the others, but the shallots I have grown have varied wildly in the number of new bulbs. I have had between 5 and 12 of various size from one.

I am not positive about bunching onions as I am only now planting them for the first time, but from what I've read I think that you only get one plant from each seed, but that they reseed them selves quite effectively.

I grow all 3 but rarely harvest the walking onion bottom bulbs except to make room for something else or to harvest the topset bulbils. Mine are Catawissas I believe--the topsets sprout and form another set of topsets.

Shallots I usually get 3 or 4 from each planted. Smaller types I get more, or I leave them be to get mounds--shallots that divided, that divided, that divided.

For multiplying onions, I'itoi onions usually divide in 10 I believe. Potato onions depend on the bulb size planted, larger ones make 3-5 smaller ones, smaller ones make 1 or 2 larger ones if I remember correctly.

Hope this helps.