Does your school provide you with an adviser? Are there requirements for your major? After taking care of requirements, I'd focus on what classes you believe will benefit you most in what you want to accomplish or learn and what topics are of most interest to you.

"Intro to Plant Science" is a great course!!! I'm already conducting scientific experiments (vegetative propagation) in my kitchen.

I'll meet with an adviser in a few weeks to discuss which course should be my next one.

Have You ever heard of that unique and useful device known by most as A LIBRARY? So many of the botanical/ horticultural courses offered by "institutions of higher learning" are pretty rinky-dink. An interested individual could learn much thru a decent library and the cost is beautiful.

It would help to know just where you want to go with your learning. That would let us know how to prioritize things.

One guess is that you are interested in working on development of community gardens and urban intensive agriculture, and need to understand enough of the basics to be able to make these projects work. And also need to be able to talk intelligently to the master gardeners et al that you will need to work with.

But I could be worlds wrong.... .

The "which courses to take" answers are wildly different, depending. If my guess is close, then there are some things that are better learned in class. A great many others are fine picked up from books or other sources, once you have a basic foundation of courses that help you understand what you're after. Is that the question? Which courses give you enough foundation?

I have graduate degrees in humanities, so it's not important that I "major" in a plant science area; I just want to learn as much useful material as I can.

Rote learning isn't going to ward off senility as well as classes in mathematically based subjects such as calculus, physics, or electrical engineering.

I have a biology degree for teaching and I also have gardened for years. I would suggest a beginning geology course. This class deals with soils, rock, minerals, etc. in which plants need. Also, a botany course which would explain how plants functions and identification of them. I found these courses helpful in my gardening. I praise you for taking taking additional courses. Good luck!

My original bachelor's degree was in the classics- Latin and Greek. I then went back for an undergraduate program in horticulture in my 30's.

I would suggest a handful of core classes that, for me, turned out to be of the most lasting and general use, regardless of your ultimate specific aim.

Soil Science
Plant pathology
Plant propagation
Woody plants
Herbaceous plants

There is a lot to be said for learning, at any age, in the programmed format of the classroom.

good luck

My undergraduate major half century ago was medical microbiology and then while working evenings at the hospital I studied horticulture.

Fast forward 50 years. I second brian_zn_5_ks' recommendations for soil science and plant propagation. To this I would add microbiology, perhaps before soil science.

You should probably want a good course in pH, buffer capacity, cation ion exchange. I don't know course covers these today, years ago they were taught in second semester chemistry. Here I got into some serious math that some above suggested.

I think that makes four course. For the fifth I would recommend mycology or perhaps better yet, genetics, where today you must surely get inundated with DNA.

Farmboy never clarified if he's after another degree or just wants to take classes. I'd strongly suggest he add an entomology class to his list.

It sounds like your real interest is in horticulture, not plant science, which are 2 completely different worlds. My Botany class had next to no horticulture information, for the first two-months we studied photosynthetic bacteria, then moved up the Kingdoms..Protista...Fungi...we only got to plants in the last two months of class lol. Spent a lot of time under the microscope! The only thing I learned how to grow was myxomycota in my closet! (The wife was not keen on the slime mold but it was too fascinating to resist!)

Sorry I had more to say in my message...just go visit the library, you will learn more about gardening in a week than 5 college courses can teach you. Plus it is much less expensive.