Cats need greens to provide vitamins (folic acid), aid their digestion, assist in removing fur balls and increase roughage in their diet. Cats will naturally eat grass when out on the prowl, but the grass they eat may well be tainted with chemicals or urine and faeces from other dogs and cats. When you grow your own grass you can be sure that it is clean and fresh. When the grass is about 6 to 7 cm (2.5" to 3") high, its ready for your cat to enjoy. It is also suitable for other animals such as dogs and rabbits.