I would give them a good, balanced feed now, to build up the bulbs as much as possible. They may need more pampering next year, before blooming in 2019. Also check that the amount of shade hasn't increased too much.

Feed until the foliage dies back using something like half strength tomorite. They seem to be very close to the fence and you may need to lift and move them once they died down completely.

They do look as if are undernurrished, don't they. Now is the time to feed and, if you have such, something like well rotted farmyard manure would be good as the soil looks rather thin and gritty. As you probably don't have the manure then a high pottasium liquid feed like tomato fertiliser weekly until they die down and then mulch with a rich, humus based soil conditioner

Thanks all.
Tug - no increase in the amount of shade, quite the opposite as I cut back the Cotinus quite hard last year. A good feed is what they shall have!
Thank you MG, I think you are right re the fence. I'll build them up first with a view to finding them a spot elsewhere.
Bulba - I too thought they were looking a bit peely wally, which was the basis of me thinking there was a problem. The soil isn't too bad albeit a bit stoney but I do have a half bag of farmyard manure looking to be used up as it happens.
Thanks everyone.