By Cobbers
United Kingdom 
1 Having left some onion plants in the ground over winter, they seem quite healthy. Will they develop new onions in the summer
2 similarly, I have left some parsnips in the ground over winter. They are now developing very healthy green foliage will they develop into seed heads or new parsnips?
Many thanks
19 Mar, 2016
Answers
They may grow beautiful flowers but don't look for anything to eat. It's too late.
19 Mar, 2016
If the onions had good sized (5+ cm diameter) bulbs, they will probably bloom in early summer, without producing a new and larger bulb. If they had no bulbs--and aren't bunching type--they might produce larger than normal bulbs at the proper time. There is considerable variation in behavior between varieties.
20 Mar, 2016
Previous question
« Just planted some "CHINESE LANTERNS" they look very dainty, any advise...
Your onions will grow lots of foliage but no new onions, ditto the parsnips. You 'may' be able to harvest both now but I doubt it, far too late!
19 Mar, 2016