Questions about den spectabile

[let_it_grow]

Can someone give me an idea or a picture of how big a den spectabile needs to be to bloom? I have one that's growing fast, the grower told me when I purchased it that they can bloom at that size but usually not till they are larger. It has sent out new larger canes but as they reach maturity they don't look like they are going to bloom. Can someone tell me roughly how tall the canes need to be for it to bloom