Onion tops not growing straight

Mines do the same, I just go with with. I do find when i water them more the don't fall over as much.

When I planted them they were big and fat. Two cuts later they are pencil thin. Not sure what I am doing wrong.

I buy onion tops from the grocery store, cut the tops off and plant the roots. They take off pretty good. I have about 3 bunches planted in a pot and haven't bought onion tops in a year or so from the store. I only use 4 or 5 at a time so I always have enough.

A few things can contribute to the tops falling over, from too much wind to an onion bulb planted too shallow in the soil, to insufficient light (like up against the house, so they're growing away from shade toward greater light). You might want to let the tops grow for a bit longer before harvesting--the diameter definitely increases over time.

Also could simply be the variety of onion you planted.