3 bulbs.
 
Allium Stipitatum White Giant really is a giant.  Growing to over 1M tall with an enormous globe of a flowerhead.  Flowers June and July.  Leave spent flowerheads in place for birds and hopefully some self seeding.
 
Alliums like a sunny spot in well drained soil.  All bulbs prefer good drainage and we strongly recommend adding grit, gravel or sand to planting holes to aid drainage.