Addendum after about one and a half years:
The grass has grown extremely dense and has even the heat wave survived with drought. Less well did the severe frost and lack of snow early in the year, where a large area was broken frozen. Of this, however, nothing has been seen already after the first phase of growth!
It is important, as I found out, and was confirmed to me:
1. spring fertilizing (1 x) at the beginning of the growth phase with starter fertilizer (phosphorus-heavy) to stimulate vigorous root growth
2. Summer fertilization (2 x) with Stickstofflastigem fertilizer to ensure (the beginning of June and the beginning of August) to healthy growth.
3. Herbstdündung (1 x) with potassium-based fertilizer to the lawn to make the end of September ready for the winter and to improve the frost resistance.
By "organic" fertilizer (eg horn chips, I was discouraged. This was given, among other things, a complicity in the "Frost disaster" ...
Compared to other, which is used either turf or lawn favorable places to the detriment of other areas a big difference to see ...