Visit the gardening trainers, they are in WC, KT, MS, VL, AV, & KS. You will need to be the appropriate gardening level and have sufficient gold to purchase. When you interact with the trainer you can buy or train spells, once you have purchased all the spells that trainer sells you will only be able to buy seeds, pots, decorations from him.
how do you get spells like (sun, rain and so forth)? have not been able to find any.
Talk to the Gardeners on each world as you level up gardening, starting with the one outside Goblin Tower in Wizard City. You learn the spells with gold instead of training points.