I have a fair selection of lilies in pots that perform well every year.

However, this year about half and particularly the Asiatic hybrids are
about 1/3 the height that they would normally be. 3' ones are 1' high
and compact ones barely 6" tall. Not all of the plants are affected and
some species ones are normal height. All were treated identically so I
am wondering if some nasty virus has stunted them, lily beetle has
proved impossible to eliminate and seems to get worse each year :(

It could just be shortage of water in some pots at a crucial time but
the problem affected more than half of them so I am worried that they
are infected. No obvious signs of disease apart from being about 30% of
the height they would be in a normal year. I am a bit worried that their
diminutive size this year will mean poor flowers next year.

Anything I can do to help boost them? High potash tomato feed or other?

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Regards,
Martin Brown