For each kilo of trimmings you remove around 30 grammes of nitrogen, 20 grammes of potassium and 10 grammes of phosphorous. You have to replace these nutrients. Decorative lawns need somewhat less fertiliser than lawns which are walked on or are under stress.
You normally fertilise lawns every four to five weeks from March/April, ending with a final autumn fertilisation to prepare for the winter at the start/middle of September. However, differences do exist now that long-term lawn fertilisers and special autumn fertilisers have come to the market. As we keep reiterating, you must pay close attention to the manufacturer's information on lawn fertiliser packets. This can also help to answer the question of whether you can use composite fertiliser rather than lawn fertiliser. Take a look at the mix ratio of composite fertiliser - nitrogen: phosphorous: potassium. For lawns this is ideally 10:3:3-5.