This is an Illustrated Guide to Plants.
Wizard City
Gardening Shop run by Farley Located in Golem Court

Plants He Sells:
Laugh-O-Dil-Cost 600 Gold-Rewards Rank 1-Challenge Rank 1-Like Garden Gnomes-Dislikes Stinkweed, Desparagus,White Desparagus-Requires Small Pot-Rank 2+Only-Needs Sun
Know Harvest Rewards: 2 GXP, 40-50 Gold, Shield TCs, Calm TC, Laugh-O-Dil Seed

Desparagus-Cost 600 Gold-Rewards Rank 1-Challenge Rank 1-Likes Garden Gnomes, Broken Stumps-Dislikes Stinkweed, White Laugh-O-Dil, Pink Laugh-O-Dil, Laugh-O-Dil-Requires Small Pot-Rank 1+ Only-Needs Pollination, Music
Knowed Harvest Rewards:70-80 Gold, Minion Helping Treasure Cards, Desparagus Seeds, White Desparagus Seeds

Dandelion-Cost 600 Gold-Rewards Rank 1-Challenge Rank 1-Likes Garden Gnomes, Potted Cattail, Blue Ball of Yarn-Dislikes Stinkweed-Requires Small Pot-Rank 1+ Only-Needs Pollination
Knowed Harvest Rewards: 2 (20 at Elder) GXP,20-30 Gold (70-90 at Elder), Dandelion Seed, Cat Tail Reagent, Orange Dandelion Seed, Mistwood, Ore, Bone,

Honey Sickle-Cost 1200 Gold-Rewards Rank 1-Challenge Rank 2-Likes Garden Gnomes, Weapons Rack-Dislikes Stinkweed-Requires Meduim Pot-Rank 1+ Only-Needs Pollination, Sun
Knows Harvest Rewards: Gold 30-40, Treasure Blades of all shcools, Spirit and Elemental blade, Balance Blade, At Epic gives around 80 gold and 3 random treasure blades

Boom Shroom-Cost 1200 Gold-Rewards Rank 1-Challenge Rank 2-Likes Garden Gnomes, Broken Stumps, Pet Cannon-Dislikes Stinkweed-Requires Small Pot-Rank 1+ Only-Needs Music, Water
Knowed Harvest Rewards: Gold 20-30, Spider Silk, Deep Mushroom, Mandrake, Sandstorm Treasure Card, Smokescreen Treasure Card

Stinkweed-Cost -Rewards - Challenge - Likes - Dislikes - Requires -Needs Water
Knowed Harvest Rewards: 2 GXP, 60-110 (180-190 at Elder) Gold, Smokescreen TC, Tower Shield TC, Poison TC

Helephant Ears-Cost 1200 Gold-Rewards Rank 2-Challenge Rank 3-Likes Garden Gnomes, Gong of the Oni-Dislikes Stinkweed-Requires Meduim Pot-Rank 3+Only-Needs Water
Knowed Harvest Rewards: 10 (100 at Elder) GXP, 140-170 Gold, Ore, Scrap Iron, Fire Blossom, Sunbird TC, Helephant Ears Seed

Baby Carrots-Cost 1800 Gold-Rewards rank 2-Challenge Rank 3-Likes Garden Gnomes-Dislikes Stinkweed, Silver Trumpet Vine, Trumpet Vine-Requires Meduim Plot-Rank 3+ Only-Needs Music
Knowed Harvest Rewards: (100 GXP Elder),30-40 Gold, Carrots, Evil Carrots, Flaming Carrots, Baby Carrots Seed

Evil Snow Peas-Cost 1800 Gold-Rewards Rank 2-Challenge Rank 3-Likes Garden Gnomes-Dislikes Stinkweed-Requires Meduim Pot-Rank 4+ Only-Needs Magic,Water
Knowed Harvest Rewards: 5 (50 at Elder) GXP, 20-60 Gold, Evil Snowman Treasure Card, Red Mandrake, Frostflower, Iceblade TC, Icebat TC, Evil Snow Peas

Fickle Pickle-Cost 2400 Gold-Rewards Rank 3-ChallengeRank 4-Likes Garden Gnomes-Dislikes Stinkweed- Requires Enchanted Soil, Small Pot-Rank 5+ Only
Knowed Harvest Rewards: 20 (200 at Elder) GXP, 20-30 Gold, Fries, Pearl, Diamond, 3 Pip Spells TCs, Fickle Pickle Seed

Wizard City Plant Drops:
(None Yet, Info Needed)
Plants He Sells:
Snap Dragon-Cost 600 Gold-RewardsRank 1-Challenge Rank 1-Likes Garden Gnomes, Regal Dragon Statue-Dislikes Stinkweed-Requires Large Pot-Rank 3+ Only-Needs Magic
Knowed Harvest Rewards: 2 EXP, 10-30 Gold, School Gem Reagents, Stone Blocks, Coal
Bread Fruit Bush-Cost 600 Gold-Rewards Rank 1-Challenge Rank 1-Likes Garden Gnomes-Dislikes Stinkweed-Requires Large Pot-Rank 3+ Only-Needs Magic
Knowed Harvest Rewards: 2 (20 at Elder) GXP, 30-40 (60-70 at Elder) Gold, Rank 4 Snacks
Rye Bread Fruit Bush-Cost 1200 Gold-Rewards Rank 2-Challenge Rank 2-Likes Garden Gnomes-Dislikes Stinkweed-Requires Large Pot-Rank 3+ Only-Needs Magic
Knowed Harvest Rewards: 5 GXP, 20-30 Gold, Rank 4 Snacks
Cornbread Fruit Bush-Cost 1800 Gold-Rewards Rank 3-Challenge Rank 3-Likes Garden Gnomes-Dislikes Stinkweed-Requires Large Pot-Rank 4+ Only-Needs Magic
Knowed Harvest Rewards: 10 GXP, 20-30 Gold, Rank 4 Snacks
Prickly Bear Cactus-Cost 2400-Rewards Rank 3-Challenge Rank 4-Likes Garden Gnomes, Pile of Sand-Dislikes Stinkweed-Requires Enchanted Soil, Meduim Pot-Rank 4+ Only-Needs Music, Pollination
Knowed Harvest Rewards: 20 (200 at Elder) GXP, 70-90 Gold, Rank 5 Pet Snacks, Prickly Bear Cactus Seed

Krokotopia Plant Drops:
Plants He Sells:
Pink Laugh-O-Dil-Cost 1200 Gold-Reward Rank 2-Challenge Rank 2-Likes Garden Gnomes-Dislikes Stinkweed, Desparagus, White Desparagus-Requires Small Pot-Rank 4+ Only-Needs Pollination
Knowed Harvest Rewards: 5 GXP, 40-50 Gold, Calm TC, Laugh-O-Dil Seed
Orange Dandelion-Cost 1200 Gold-Rewards Rank 2-Challenge Rank 2-Likes Garden Gnomes-Dislikes Stinkweed-Requires Small Pot-Rank 4+ Only
Knowed Harvest Rewards: 5 GXP, 60-70 Gold, Shadow Oil
Burning Snap Dragon-Cost 1800 Gold-Rewards Rank 3-Challenge Rank 3-Likes Garden Gnomes-Dislikes Stinkweed-Requires Large Pot-Rank 6+ Only
Knowed Harvest Rewards: 10 GXP, 30-40 Gold, Killer Tomato
Venus Flytrap-Cost 1800 Gold-Rewards Rank 3-Challenge Rank 3-Likes Garden Gnomes-Dislikes Stinkweed-Requires Meduim Pot-Rank 4+ Only-Needs Pollination
Knowed Harvest Rewards: 10 GXP, 90-100 (460-470 at Elder) Gold, Traps TCs, Fairy TC, Scrap Iron
Plants That are Dropped:
Deadly Ninja Fig-Dropped by Oakheart-Rewards Rank 6-Challenge Rank 6-Likes Boom Shroom-Dislikes Stinkeed-Requires Enchanted Soil, Larget Pot-Rank 7+ Only
Knowed Harvest Rewards: 50 GXP, 60-70 Gold, Skeletal Pirate TC

Dragonspyre
No Gardening Shop
Plants That are Dropped:
White Laugh-O-Dil-Dropped by Decaying Blackguard, Gurtok Piercer-Rewards Rank 6-Challenge Rank 5-Likes Garden Gnomes-Dislikes Stinkweed, Desparagus, White Desparagus-Requires Enchanted Soil, Small Pot-Rank 8+ Only
Fiery Boom Shroom-Dropped by Gurtok Piercer-Rewards Rank 6-Challenge rank 5-Likes Garden Gnomes-Dislikes Stinkweed-Requires Enchanted Soil, Small Pot-Rank 8+ Only

Celestia
Gardening Shop run by Harley Located in Celestia Base Camp

Plants He Sells:
Trumpet Vine-Cost 2400 Gold-Rewards Mega Massive-Challenge Mega Massive-Likes Garden Gnomes-Dislikes Stinkweed, Baby Carrots-Requires Enchanted Soil, Meduim Pot-Rank 6+ Only
Knowed Harvest Rewards: 20 GXP, 40-50 Gold, Humongofrog TC
White Desparagus-Cost 2400 Gold-Rewards Mega Massive-Challenge Mega Massive-Likes Garden Gnomes-Dislikes Stinkweed, White Laugh-O-Dil, Pink Laugh-O-Dil, Laugh-O-Dil-Requires Enchanted Soil, Small Pit-Rank 6+ Only
Knowed Harvest Rewards: 20 EXP, Minion TCs
Frozen Flytrap-Cost 3000 Gold-Rewards Mega Massive-Challenge Epic Mega Massive-Likes Garden Gnomes-Dislikes Stinkweed-REquires Enchanted Soil, Meduim Pot-Rank 5+ Only
Knowed Harvest Rewards: 50 GXP, 90-110 Gold, Blizzard TC, Colossus TC, Frostbite TC

Celestia Plant Drops:
Deadly Fly Trap-Dropped by Aqua Bots, Gurtok Piercer, Cuthalla-Rewards Mega Massive Epic-Challenge Mega Massive Epic-Likes Garden Gnomes-Dislikes Stinkweed-Requires Enchanted Soil, Meduim Pot-Rank 6+ Only
Knowed Harvest Rewards: 300 GXP, 130-220 Gold, Deep Mushroom, Infection TC, Scarecrow TC, Bone
Maelstrom Snap Dragon-Dropped by Hydro Mechs, Gurtok Piercer-, Oakheart-Rewards Rank 5-Challenge Rank 5-Likes Garden Gnomes-Dislikes Stinkweed-Requires Enchanted Soil-Requires Large Pot-Rank 7+ Only 
Crown Item Plants
Happy Holidaisy-Sold in Crown Shop around Christmas Time-Rewards -Challenge-Likes -Dislikes -Requires -Rank + Only-Needs Music, Water
Known Harvest Rewards: 10 GXP, 50-90 Gold, Rank 3 amd below Snacks,
Ninja Fig-Sold in Crown Shop around Christmas Time-Rewards -Challenge-Likes -Dislikes -Requires -Rank + Only-Needs Magic
Known Harvest Rewards: Evil Magma Peas-Sold in crowns shop *1250* Requires Medium Plot - Rank4 -
Rewards-TCs (Tower Shield/Triton/Poison/Polymorph Ninja Pig/Feint/Earthquake/Cleanse Charm/Pierce) Reagents- (Aether/Aquamarine/Pealr/Golden Pearl/Sandstone) Elder Harvest guarantees re-seed also a rank 9 mega snack (Captain Cantaloupe/Fancy Yogurt/Cherry Tomato/Golden Wheat Bread/
Deadly Helephant Ears-Sold in crowns shop *750* Requires Medium Plot - Rank 2- Rewards TCs (Earthquake/Humongofrog/Judgement/Minotaur/Pierce/Scarecrow/Tempest/Tower Shield/Unicorn) Reagants (Diamond/Pearl/Sandstone/Sunstone/Aquamarine) Elder Harvests guarantees re-seed also a mega snack ( Baby Carrot/Crab Apples/Cubby Broccoli/Dragonhorned Melon/Flowering Pineapple/Green Tomato/Sun Fruit/Yellow Corn)
Pink Dandelion-Dropped by Temple of Storms Mobs, Krokohamen, Aqua Bots, Nirini Sentries-Rewards Rank4-Challenge Rank 4-Likes Garden Gnomes-Dislikes Stinkweed-Requires Small Pot-Rank 1+ Only-Needs Pollination, Water
Knowed Harvest Rewards: 20 GXP, 30-70 Gold, Black Pearl, Cyrstal Vial
Silver Trumpet Vine-Dropped by Piscean Centurions, Optio Vitale, Ptolemos-Rewards Mega Massive Epic-Challenge Mega Massive Epic-Likes Garden Gnomes-Dislikes Stinkweed, Baby Carrots-Requires Meduim Pot-Rank 1+ Only
Knowed Harvest Rewards: 300 GXP, Cleanse Charm TC

King Parsely-Dropped by Gurtok Piercer-Rank 6 Rewards-Rank 6 Challenge-Likes Garden Gnomes-Dislikes Stinkweed-Meduim Pot-Rank 1+ Only-Needs Music, Sun
Knowed Harvest Rewards: 100 GXP

Couch Potatoes - Sold in crowns shop *1500* Requires Large Plot - Rank 3 - Reward TCs ( Amplify/Conviction/Empower/Fortify/Infallible/Vengeance) Reagants- (None) Snacks- (Captain Canteloupe/Fancy Yogurt/Golden Pizza/Golden Wheat Bread/Jar of Jelly Beans/Killer Tomato/Shanta Pudding/Taco Town Special) The Elder Harvest will include one of the mentioned Megas and a re-seed
Angora BunnyEars - Sold by Roger the Shrubber(2400 gold) - Drops from the Emperor's Attic Hoard Pack Requires Medium plot - Rank 4 - Reward Seeds: Baby Carrots/Fickle Pickle/Angora BunnyEars
Thank you to Deathshard who gathered and made most of this guide possible
Thanks to the following people who helped with the guide:
Jacob Taleheart, Paige Moonshade, Misthead, Evil Toast, Susume, tamlfra, TiM_FeRNo, spike491, Mythtress_Tara, Light Knight, ninjapigman, kandyj, Willowdreamer, Sorrieah, MikeStrath, MsSandy, lukin
Helpful Info about Gardening here.