It is also the juices of the grass that cats are interested in. It is known that grasses contain folic acid, a vitamin that is vital to cats as it helps in the production of haemoglobin. For a cat to be deficient in folic acid would stunt its growth and may cause anaemia.
If your cats have no access to a garden why don't you plant them some herbs to nibble on. You can purchase catnip and chamomiole and even alfalfa sprouts , just add some water and within a few days your cats should have a lush supply to chew on. Wishing you happy cats.