Unfortunately, cat grass is kind of a "one and done" plant. The bunch you sow in this planter will grow as your cat eats it, and you may even need to trim it back a couple times, but it will only thrive for a short amount of time (three weeks to three months depending on the type of cat grass you're growing). After that, you'll need to add some more cat grass seeds to the potting soil. You can sow seeds at various times, though. You don't have to wait for your first crop to die completely before you sow more.