I'm thinking about putting some walking onions in the garden, and was wondering how fast they will populate the garden.
They aren't incredibly fast, but do spread. A single plant I put in about 5 years ago is now a solid patch about 1' by 3' long. I have done some weeding out of plants that spread where I didn't want them, but not a lot. (ETA: This is in zone 4b.)
It's a plant I think anyone who likes green onions should have. I use the green onions from early spring through June. After that, the sets start developing on the top of the plants and the greens are no longer tender. The bulbs themselves are too small to use in my opinion, but I do use them on occasion when I run out of onions.
I planted some last year and if anything the patch has shrunk. So, at least in my climate it takes some time for them to spread. They were planted into a bath being used as a raised bed into potting mix so no competition from weeds, and intercropped with carrots. I'd imagine in less favourable circumstances they take a long time.