I had a LOT of trouble with hairballs with my new 9 year old cat. I tried the “cat grass” from the store but it didn’t work well. Then I remembered my old cat, back when she used to go outside, used to eat crabgrass. So I dug up a clump and brought it inside. I kept it watered and over a couple weeks the hair ball issue resolved. I’ve replaced the grass a couple times when it stoped growing. He chews on the stems regularly and the system seems to be working well now.