In article , Charles Thorpe
writes
Hi
I've still got some spring onions growing which are now quite large and
looking very healthy and sturdy.

I might be a fool for thinking so, but if I leave them alone, will they
continue to grow into onions next year, or are they different plants?

Some ornamental onions (alliums) are grown as perennials for their
flowers. If you intend to eat the bulbs though it would be better to
have them out and store them before they begin to bolt.
--
Alan & Joan Gould - North Lincs.