By Demented
United Kingdom 
I have a 5 yr old, self-fertilising cherry tree which has not as yet produced flowers let alone fruit.
This year I have noticed the end leaves are curled tight. On further inspection I notice that these leaves are harbouring many small ants. Can this manifestation harm the tree and has anyone any suggestions as to how I can get the thing to flower. Tried all the usual advice; pruning, feeding etc. Am about to yank it out!!
25 Jun, 2016
Answers
The ants are feeding on aphids (or their droppings to be more accurate). Put a grease band around the tree trunk to stop the ants getting up the tree and spray the tree against the aphids for a start.
5 year old tree is a bit young to start producing fruit. You may well have to wait a few more years yet.
25 Jun, 2016
If not grease you might try Tanglefoot if it is availble in the UK. I don't know the reason why but never apply it directly to the tree bark. The directions will show you how to do it.
25 Jun, 2016
RHS advice here regarding Cherry Blackfly,including treatment
https://www.rhs.org.uk/advice/profile?PID=488
26 Jun, 2016
5 years is still a bit soon. Mine waited 8 before it flowered. Re the curled leaves see my question on the same subject a few days ago.
25 Jun, 2016