I live in a fairly unique climate in the US (maritime, like England), and as a gardener, I'd say your planting picks are reasonable for my area.
A few general thoughts:
People have said it here already, but container gardening+++. It's how a lot of people get started gardening, and therefore is a compelling product for your market niche, inexperienced gardeners. Pick a great product and sell it, I think the 'insta-garden' pitch is likely to be a big seller for you.
I would personally recommend you resell earthboxes, they're fabulous and have good online marketing if people care to learn about them. Partner up with local organic soil and fertiliser providers, and get them to do the shipping for you if you're worried about logistics. Earthbox might cross promote you if you got in touch, your site is cute and cool.
Second, I think you should find a better source for gardening advice than google lucky searches. There are a lot of possibilities here, and eventually crowdsourcing _local_ tips would be awesome -- as you know, gardening is always a really local activity -- but you might just hire a well-'spoken' vegetable gardener to write up instructions, or look for a gardening book writer who wants to cross promote on your site.
That is all, and good luck!
Also, your site is overloaded and Heroku is complaining sometimes. Congrats.