Dwarf pampas grass thrives in well-draining soil that is rich in organic matter. The ideal pH level for the soil is between 6.5 and 7.5, which is slightly acidic to neutral. The soil should also be able to retain moisture, but not be too waterlogged as that can lead to root rot. Adding compost or organic matter to the soil can help improve its texture and fertility. Overall, it is important to ensure that the soil is well-draining to prevent water from accumulating around the roots of the plant.