Answer: I don't know of any internet sites that offer courses in horticulture. Your best bet might be to contact your state's Extension Service and see if there are any Master Gardener training courses in your area. I'll give you some interesting web sites to visit, where just by browsing you can learn a lot!
National Gardening Association: http://www.garden.org
The Virtual Garden: http://vg.com
Internet Links: http://www.gardeningbc.com/links.html
Master Gardener Database: http://leviathan.tamu.edu/ls.mg
Hope this helps get you started.
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