I am not sure how nandina will act/react in a vase. To propagate take a cutting 2-4 inches ling remove all but tip leaf. Apply 0.8% IBA (rooting hormone) stick in well drained soil & mist Takes 25-60 days to root.
if forms roots in water they (the roots) will not survive in soil. so as soon as any roots start to form must move to soil & mist till able to stand on its own (severay weeks to a month.

I have accidentally grown Nandina domestica nana in a vase - left the arrangement for a very long time...I transplanted into a soil / perlite mix and they are going well - not alot of growth but still very much alive...I'll put them into the garden this Spring and see how they go (Z5).