Mimosa does not flower
 

I have an Acacia Dealbata (Mimosa) tree which is just under 2 years old. The tree itself is thriving and healthy, being planted in a single bed in S-East facing garden. However, much to my dismay, no flowers. I have asked at the nursery where I purchased the tree and was told that it needed Potash to flower, but I have my doubts this will work. Does anyone have any ideas as to why I have no flowers and how I can get it to flower (assuming it isn't a male, that is)? I have to admit to purchasing the tree for its flowers.