I buy bottles of white vinegar for around 30centimes a litre and put it everywhere, kills everything too and is not dangerous to animals. Keep topping up the treatment and you will see a difference and it also clears paving of moss and algae too.Only do it if no rain forecast so it can soak in neat and do not skimp on the application. Otherwise salt is also a good weedkiller especially the coarser stuff and cheap too!