G4 is a green expansion that is made up of a group of 9x9 plots for a total of 81 plots or 1,296squares which can be used to place items; It was introduced, with the release of the Story of Sakura farm, and is the fourth (4th):
Of six (6) green expansions found on the Story of Sakura farm though to the ??? farm.
These green sections do not require you to pay any cash, coins, gain consent, nor do they require you to perform any tasks before it will allow you to gain access to itself.
The Avalon farms (Wilderlands and Kingdom) both have shared storage capacity with each other; increased by 250 items to 1,500 items, on these two (2) farms only, when the Kingdom farm was released. The remaining farms, without shared storage, still have 1,250 max capacity. The Shipping license for the Wilderlands farm also gives you access to the Kingdom farm items.