Couch potatoes are great for mega snacks, but a bit of a pain to get the seeds for, you can farm for them in Grizzlefeim but the drop rate is pretty low. Prickly bear cactus is a good source for mega snacks for those who don't have the patience to farm couch potato seeds; you can buy them for gold and don't need to buy many as the seeds multiply, but the snacks aren't as good, they give rank 8 snacks instead of rank 9 like couch potatoes.
I also grow plants for reagents. I read a guide once that refers to Fickle Pickles as the "Swiss army knife" of reagent harvesting, they give a great variety reagents as well as some useful treasure cards. When I need black pearls I usually plant some pink dandelions, they get dropped by so many different creatures you will have plenty of pink dandelion seeds without even trying. I have been growing silver trumpet vines to try and accumulate vine and braided vine against future need. Silver Trumpet vine seeds get dropped fairly often, but if you need more you can get them by growing regular trumpet vine plants, sometimes they give the silver seeds when harvested. King Parsley is the top of the heap for reagent gathering, they occasionally drop amber, several other reagents, and a variety of good treasure cards. I haven't ever had a King Parsley seed drop. I bought one seed from the crown shop, and accumulated more as the seeds do multiply, though very slowly. I tried fish on a vine, but hate the plant, the darn things draw level 4 pests, burning more energy to get rid of than I like to spend. Besides, it creeps me out how the fish always turn towards me and start barking when I'm not paying attention.
If you have crowns to spare, Key Limes are fabulous for ranking up your gardening skill level. Otherwise, pink dandelions are a good choice as they can be planted by a level 1 gardener. If you can get couch potato seeds to drop they can be planted when you reach level 3, and give gardening experience much faster then pink dandelions.
For the looks I love moon flowers, alligator pear trees, fish on a vine, and my ultimate favorite, angel oak For the rewards I like couch potatoes (mega snacks nice treasure cards), EMP (well duh lol), cornbread fruit bushes (golden wheat bread which is a mega snack), and ummm there's probably more but I can't remeber lol.
For my lower level wizards I like Stinkweed for a virtually endless supply of Smokescreen and Poison TC. And Pink Dandelions are great for some of the rarer and more expensive reagents like Black Pearls, Black Lotus, Bronze Gears etc. And both of these drop a lot of their own seeds so you can have a constant rotation. They also use a small plot so in groups of nine (3x3) you can cover them with the medium, 8 pip spell circle in one shot.
As a grand master gardener, i dont really plant for regents, tc, pet snacks or any other drop. I garden because i love to garden, my personal favorite has to be a tie between dandelions and the moon flower, mostly because how magestic these two look, btw redecorating my red barn farm, be done soon keep an eye out for it in the house tours.