  We study the mechanism of formation of Bose glass (BG) phases in the spin-1
Bose Hubbard model when diagonal disorder is introduced. To this aim, we
analyze first the phase diagram in the zero-hopping limit, there disorder
induces superposition between Mott insulator (MI) phases with different filling
numbers. Then BG appears as a compressible but still insulating phase. The
phase diagram for finite hopping is also calculated with the Gutzwiller
approximation. The bosons' spin degree of freedom introduces another scattering
channel in the two-body interaction modifying the stability of MI regions with
respect to the action of disorder. This leads to some peculiar phenomena such
as the creation of BG of singlets, for very strong spin correlation, or the
disappearance of BG phase in some particular cases where fluctuations are not
able to mix different MI regions.
