Colorado State University has their popular Master Gardener Course online and on sale right now. The class fee is usually $654 but is currently 20% with code GARDEN2020.
Click here for an overview of the class:
https://www.online.colostate.edu/global/docs/programs/CertifiedGardener_Flyer.pdf
Registration:
https://www.online.colostate.edu/badges/certified-gardener/curriculum.dot