Allium question

A quick one for the experts. Alliums are new to me and I am wondering if they reliably return each year or are they better treated like tulips (might come back but better of getting new ones each year).
The reason I ask is last year I planted some large christophii that bloomed well so I added some more this year along with a few white giant and purple sensation. This year it looks like the new bulbs are fine but some of the old bulbs from last year seem to of multiplied into a clump of smaller plants (not from seed, from the bulb) and have no flowers. Just wondering if I should leave them or dig them up for the space.
Thanks

 

It sounds like they are trying to naturalise, how well they will do at that will depend on your local conditions I guess ... personally I would leave them and see how they do next year. Christophii aka Star of Persia have naturalised around here, and can be seen growing in big clumps in a local Victorian cemetery and the Commons. The flowers are not perhaps as large as the ones from big bulbs from a plant nursery, but still very attractive to my mind.

 

That is what happens with lots of Alliums. Try feeding them heavily as soon as the leaves appear. Those types are winter growers so food is needed in autumn.
We have clumps of Purple Sensation types with 6 or more flowering stems.