Use neutral humus, suggested is to take the earth of a molehill. Mix it with sand in ratio 5:1. Sand contains important minerals and leads to a warming of the soil. It leads to a better moisture and a more decompressed mixture.
The PH value should be around 6,5.
The soil hast to be fertilized with Nitrogen, there are several different kinds of Nitrogen fertilizers, one of them is Kalkammonsalpeter (NH4NO3)(KAS), a fertilizing granular. It contains 27% of Nitrogen.