I wouldn't put it straight onto flower border, mixed in your compost heap and leave till Winter or early Spring would be best. Then the worms will take it down for you and mix it in.
Thing is samantha, if you use it on its own its liable to just burn your plants, mixed in with other stuff it's beautiful!
I wouldn't apply now, your plants will be coming to an end soon and by feeding now you are likely to promote growth which will be soft and could die in the winter. Spring and early summer is the time to feed.
i don't feed my borders at all, only compost in the winter, I think the soil, left alone, will re generate by itself.
others don't agree with me, but there's far too much spread, trickled poured onto the soil.
tubs and baskets however get fed weekly.
I just chuck everything I have got into the compost bins, if some horse muck is available, it goes in there as well. Sometimes I buy a bag of well rotted farmyard manure to add.
In December the whole lot gets put on the beds.
Trees won't need feeding though, but spread what you have got around the perennials, the worms will take it down.