"The Silo is the place where you store your Food. A full Silo will mean you are always in the position to go into battle. Upgrade your Silo to store more Food and to be able to fight more fights."
Food can be stored in the silo, freeing storage capacity for farms. Since a farm cannot produce any more food when it's full, it makes sense to transfer its local storage to the silo.
To be able to accumulate as much gold or medals as possible, players can save up food in the silo and then in farms and then launch a series of attacks until food reserves are depleted.
The higher the silo's level, the more food can be stored. From level 5 on its capacity is the same as the four farm's capacity at the same level combined. The silo is maxed out at level 18.
Upgrading the Silo also raises the maximum level of the Farms.