Massive Planet for terrain

I want to use UE4 to make a massive earth-like planet that a space ship can fly in a out of and land on but i have no idea how to paint that much foliage it would take years any suggestions?

The easiest way would be to use an algorithm or a overlay map that can be used to define areas where the engine will place foliage. The down side if these methods is that they leave room for errors, like floating foliage or other glitches like that.