Not sure what you are really asking. Gardening won't give you any experience towards getting to the next world. The experience/rank from gardening is totally separate from player levels. If you just want to garden and level up in that. I would decide on what you want to grow first. I like couch potatoes, they are low maintenence and give mega-snacks at elder. You can farm for them in Savarstaad Pass in Grizzleheim, all the mobs have a chance of dropping them. Whatever you plant, plant the same types as closely together as possible (so you can use large area needs spells to fit as many as possible). Pay attention to likes/dislikes of seeds. Do not plant dislikes in the same general area, it slows growth a LOT. Likes speed growth. Look up the plants you plant on central, it really pays off to give them as many likes as you can.
Gardening is its own thing and has its own levels similar to crafting, it doesn't count to character XP, only gardening XP. If you haven't done tutorial yet go see, Farley-or which ever brother is there- in Golem Court. Beyond that stick to the same or complimentary plants, ones that like one or each other. Plant close together, avoid dislikes and keep their needs satisfied and pest away. Also check out W101 Central for detailed info in specific plants, as depending on type and level can give great harvests beyond Gardening XP. Good luck.