I don't have have `much' trouble with moles/voles these days but
I did at one time - they would eat my tulip bulbs and any other
bulbs I planted....got two cats and problem disappeared.
However, a friend of mine does have problems with her bearded
irises and the mole/vole critters and she started to put moth
balls around the iris...I don't know how far away from the plants.
She has a nursery in Vermont and it seems to be going okay for
her....I don't know what chemicals moth balls are made of and
this is just hearsay (since I never have done it) but I guess
it doesn't harm the iris.(?)
I do not advocate chemicals in gardening but I know some folks
on the do use them.
The smell would keep me away,
Ellen email@example.com Lancaster, NH The 3rd Zone.....