Heroes 5.5 WarGame Edition - Tactical Edition.

Farms double the current growth rate because the base +10 militia per week is not very useful. Currently, farms under a Castle or Stronghold will increase the militia growth from 30 to 60.

If farms will boost unpopular units like militia, dancers, minotaurs... then it will be okay. But for popular units like beasts or Rune Priests, such a large boost is not needed. In my opinion, the optimal solution would be to make a 3rd-tier growth boost ("farms") for only the least popular unit in each Castle.