I think my overwintering onions are in need of a January detox. They are green but look very poorly with little if no growth after planting out in October.
Pepod
They will not be growing very quickly at this time of year. Mine put on a spurt when they were first planted in October and early November but since the frosts and cold weather started they have made little progress. Hopefully that is all it is and once the weather picks up, so will your onions.
Likewise - all the way down in 'sunny' W. sussex and my winter charges are looking a little sorry for themselves. So would I if I had to sit out in the winter weather but sure they will romp off.
Same can happen with lettuce. They can sit for weeks with cold temperature (-9 to +6 nights over winter in Spain) and then grow off again happily when it warms up.
Sure your onions will do likewise
Mine are dormant too, but I know they will pick up later on ...