I have feeders up all year. The opinions seem to have shifted a bit, some used to say you shouldn't feed during the summer but it appears now that it's fine, these things come in and out of fashion!
I use sunflower hearts and black sunflower, the bigger finches (greenfinch/chaffinch) seem to prefer the black ones and they are cheaper! The hearts are demolished by goldfinches, I get them in flocks of a dozen to 20 at a time, lovely little things. Goldfinches also like nyger (niger/thistle) and the useful thing is that they are the only ones which can get them out of the feeders with the very small holes, so they do tend to last longer between refills.
I've noticed that the robins in my garden have "learnt" to take from the feeders, they never used to but will now.
One slight fly in the ointment is that a sparrowhawk seems to have moved in, it perches in my ash tree regularly which doesn't go down well with the little birds!
Still, they have to live aswell.
I've just ordered another load from
Brinvale , trying some different mix this time. Brinvale can be thoroughly recommended, postage is free above 10kg and when they say next day delivery they mean it, so far totally reliable.