There are a few friends in my community who took the
local master gardener program. It was free. The only problem with it for us is that it is given at a facility close to a two hour drive away. They all said that they learned quite a bit from the program. In exchange for the free course, they had to man the phones to
answer questions for so many hours a month. I don't recall how many because i wasn't interested in driving two hours each way.
Personally I think the term Master Gardener implies a higher level of expertise than the course provides. I gather that the course is really good for people who aren't experienced, but all the graduated master gardeners here are hardly a master at
gardening. Not to belittle them, but the course isn't as expert level as the title implies.
For anyone wanting to learn about
gardening, the Master Gardener program is probably a good step to take.