Problem with Old ceramic jars

I've been collecting very old ceramic jars for years (no holes in the bottoms). They are just collecting dust on my plant shelves in the house. Some of them I'd like to put out in the garden. The problem is they fill with water and mosquitos love it. I've put them on there sides, upside down (not thrilled with that). Because of the age of some don't want to put holes in the bottoms. Any ideas?

 

Mosquito dunks??? One in each one every few weeks. They work great. Look like little donuts.

 

Thank you so much I had almost given up hope on the idea.

 

Thanks Toni