Well normally, after cutting back hard, you'd feed with a balanced fertiliser such as Growmore - however, this assumes you've carried out the procedure before mid June and not now. Its too late to feed now and actually, its too late to have cut back so hard. The reason for that is you don't want to force new growth, either by hard pruning now, or by feeding, which won't have time to harden off properly before winter sets in. With any luck, they'll get through the winter, specially if its mild and you live in the south or west, and you can give them a good feed next spring, as growth begins.

The bad news is that Escallonia is about the worst hedging anyone can have these days, due to rampant and untreatable Escallonia Leaf Spot (https://www.rhs.org.uk/advice/profile?PID=108). I've had to take out and destroy all my once-lovely Escallonias, and am heartbroken. :((

I'm getting rid of my one bush too. It has never needed feeding though, being very vigorous without any encouragement!

Ditto. Dug up my Escallonia Iveyi hedge as I got fed up with the leaf spot, yellowing and bare lower stems. Planted a yew hedge instead which has proved trouble-free.