There a section of the yard between two ash trees at the border of the yard about 8 foot apart. Some day lillies grow there at the moment. They do ok there, but it's too dark so they never bloom. I was thinking about growing some Hellebore instead. The soil is alkaline 7.5 and may be clay-ish underneath the top soil.

Will Hellobore grow underneath an ash tree?

What cultivare should I grow in zone 5b?

What companion plants?