This is how I greatly profit with gardening. Works real well with Rank 5+ spells!
1.) Buy/Obtain your seeds 2.) Plant a few(5-12) 3.) Harvest as much reagents/cards/snacks/etc. as you can before elder 4.) Time it right and let them start to die before elder 5.) Revive the plants(this puts them back to their early stage) 6.) Reharvest over again!