You can't -it'll grow at its own pace, according to the nutrient and water available. Too late to feed now, but you can give it a general feed in Spring with something basic like Growmore granules (do you have those there?) and just make sure you keep it well watered when its hot and dry.

Well, that ´s what I am doing, although I added biological longstanding fertilizer in May (the trademark you recommended are not available here, we have different others). Yes, I think, better lay it on nature.
Just was cuirious, as books usually says that this type I have (Etna) is fast growing, but this year it grew up only about 10 cm, although the leaves are very rich.

Well, that's interesting, a new variety - doesn't get as large as the basic one, said to grow around 6 inches a year, which is around 10 cm, so its doing okay, eventual height only about 8 feet. thanks for mentioning it, didn't know it existed, could be very useful indeed.