I leave all my Allium seedheads alone until they break away by themselves later. The seedheads provide interesting contrast to other plants & flowers. This way, I get longer lasting benefits from the bulbs, considering how expensive they are, especially Globemasters.

Thanks Pitimpinai for your input. I will leave them on next year. I thought they were like daffodils and tulips -- that you cut the flower off after it is done blooming because you don't want them to go to seed. You learn something new every day with gardening. Thanks again.

If you let the globemaster and purple sensation go to seed, will it take too much energy from the bulb that next year the bulbs will not produce as big of flowers?
I read somewhere that one of these varieties produce sterile seeds. Does anybody have information on this? Thanks. Geezer

My 'Globemaster' did not produce seeds. The ones that were well fed and not crowded by other plants came back the same size as before and produced baby bulbs.

I'm deadheading my alliums - even the sterile ones, and dug up my alliums afterwards. They are coming back each year - whitout any decrease in bulb or flower size.