How to rotate a gradient in the node editor? How do I rotate a 90% gradient in the node editor without rotating the object
(see attached picture). Can I do this in the space properties editor or I probably need to add another node? 

All I want to do here is to keep the colours exactly the same, but 90% rotated in horizontal direction.
You use the Mapping Node, add it with Shift-A>Vector>Mapping. Don't forget to add the texture cordinate into the mapping node, it will not work otherwise.



You will then need to tweak the Y and Z values. To get 90o You will need to set the Y one to 90o

Here is it at work: