I used neem on my hostas. Just be careful to dillute it in water and don't apply it on a sunny day. One of my hostas' leaves crinkled up after I applied it, I think because the sun hit it before it dried. It never fully recovered that season.
I believe that my Neem oil had a dilution recomendation with warm water and maybe one other thing. The bottle was obtained at Revy in Canada and was 10.00 for 100ml's. I misted it on in the recomended strength and Yes I did not have them in the sun.