Overwintered onions have very skinny bulbs....

I'd planted some Japanese overwintered onions in late November last year where they sat doing very little (understandably) over the winter months. This past few weeks milder weather have really set them off though, and, after having a furtle, the bulbs themselves seem very emaciated. There is good top (stalk) growth, growing about 8" this last month,  but the bulbs themselves seem very feeble. I dug in some Growmore when planting and have chucked on a bit of pelleted chicken manure (as per John's advice on here) but would some Fish, Blood and Bone help? (not that'd it do much harm  )

As Mum says, they won't be ready to harvest til July/August so let them be and feed again in 6/8 weeks. Make sure they're watered!!