This has bugged me for many years.  The leaves of all of my tall alliums turn yellow at the tips starting before they even send up a flower. This includes big and little ball varieties.  I've never had the problem w short varieties like A. moly, or A karataviense. The thin-leaved ones like A. flavum and A. pulchellum and A cernuum may yellow a little early, too, but I don't notice because they're so thin anyway.  But taller varieties like A atropupureum, A azureum, Globemaster, rosenbachianum,  w strap-like leaves always look terrible for me. A albopilosum, (aka christophii, Star of Persia) generally doesn't do this even though it is a large flowerhead perhaps because it has a fuzzy leaf.

Does anyone else experience this?  What causes it?  What can I do to prevent it?

Thanks for your assistance.

Kitty