There are many answers for this kind of question and they were listed below: through seeds despersal by a process called propagation human cultivation, etc.
A plant breeder is a specific type of breeder that uses certain methods to create varieties of a single plant. E.g. tomatoes can be changed in colour, size and shape just by simple mixing of seeds....
actually you dig the hole twice as wide as the plant. here in Florida we add soil amendments. hence our saying; put a five dollar plant in a fifty dollar hole. also make sure the top of the rootball...