Florence Fennel-growing on/feeding?

I usually give the first lot (as in the ones you have growing now) a dose of chciken pellets mid June, but they they do need to be eaten fairly soon or they will bolt  One of mine already has a long immature flower stalk visible.

Spwed the next lot 2 weeks ago --- these should have less chance of bolting and so will give bigger bulbs (I hope  )