Purple Sensastion (Allium) Flowering onion. http://aekohy.notlong.com 28 May 2008 Allium hollandicum, 'Purple Sensation', Flowering Onion. This beautiful Allium flower is one of my favouites. It is almost shaped like a purple snowball. Some seeds were allowed to drop, and there are numerous small plants forming, so I should have a large cluster next year, which should be most attractive.