Don't really understand what you're expecting to show up in your sims inventory or grow? What gardening cheat? The one to improve your gardening skill? They don't just give you items. What is it exactly that you're expecting or wanting to happen? If you can explain that it'll be easier to help.
http://www.carls-sims-4-guide.com/skills/gardening/If it's the different seed packets you're after, you get new ones (available for purchase) at 10, but you still have to buy them first.