I tried the castor oil treatment last fall, using a hose-end sprayer as described on the nhhostas website, but I still had two to four hostas damaged by voles.
I know not to use unscented castor oil, but how can I be sure mine is unscented? Should it have a strong odor? Mine does not -- but it was advertised as being useful against voles.
Any tips for rejuvenating a hosta that has been partially decimated by voles?