Organic earthbox-style garden

I'm looking at setting up some organic diy earthbox-style boxes. I've got a lot of experience with raised garden beds but just want a few small container gardens this year.

I'm REALLY confused by the fertilizing suggestions. I'm used to doing a lot of side dressing and foliar fertilizing but that obviously won't work on these. What is the easiest, safest, most efficient way to fertilize a box like this organically? Thanks!

Chocolate Cherry Tomatoes, and Purple Cloudiness carrots, or plant a few conventional vegetables like eggplant and cucumbers. Furthermore, spices are consistently an incredible decision for an EarthBox