Mark, the modified mix Al recommends is a good place to start, but are you planning on covering the container and relying upon a strip of fertilizer on the surface to feed the plants? This is critical because if you will use the cover/fert strip you really need a fast wicking potting mix and this means peat and vermiculite. What I often tell people getting started with Earthboxes where a cover and fertilizer strip will be used is that the system was designed with peat based mixes and it works very well with them so give that a try for a year. It will give you a good frame of reference for tinkering in subsequent years. Assuming you do not wish to do this then: I would encourage you to make a mix and set it outside to see if it will keep the surface moist for a couple days before committing. This is if you will use the cover and fertilizer strip. If you won't use either then Al's mix (original or modified) will work fine. Keep in mind my experience is in Wisconsin, somebody in a hotter/drier/windier climate might need to modify a bit. Even with the cover on, the wind gets under it from the holes we must cut for the plants. This wind may not seem like much, but it can quickly dry the surface. You really do need to test though, that's the best approach. Just do it outside. I say this because I made the mistake of evaluating how well various materials wicked *inside* (I was going through an endless winter and wanted a gardening 'project'). How something wicks indoors is waaaay different than how it wicks outside due to temp, wind, humidity etc. Again though, you really only need to modify Al's mix with fast wickers like vermiculite or peat if you want to use the cover and fert strip. One last tip, if you find that the very surface goes and stays dry, but an inch down it's moist you can simply bury the fertilizer strip an inch under the surface. This gives more latitude in compromising between a coarse mix that drains well and one that can wick fast enough to keep that fert strip working. Happy growing.

No, seeds starting mix is finer so that roots do not get torn up when you pull seedling apart when separating community flats/pots. It is mostly vermiculite peat moss and a bit of lime/dolomite to adjust pH. Potting mix is coarser and usually contains composted materials such as pine bark and other (originally) woody materials, often with a fluffer such as perlite or styrofoam, and lime/dolomite for pH adjustment. It can be used for starting seeds if you are not planning on pulling the plants out of the mix (I use it for starting everything). Potting soil is often much denser/heavier because it contains actual soil, I have seen it advertized for things that are to be permanently grown outside in containers like shrubs in planters, but someone else might have more info on this than me. Potting mix is usually better for most things than potting soil. For all of them you would have to check the bag to see if they contain starter fertilizer.

Yes thse are the right ingredients, but the recipe is not as important as the reasoning behind it. You need fast drainage and for that you need a large particle size for the medium. The ratio of those ingredients is going to depend on the plant being grown and the environment in which it is grown. For instance a jade plant in Arizona is going to need a mix that retains more moisture than a jade plant in Florida or Louisiana. Most people underestimate how much moisture gravel can retain. I have succulents in a 3:1 mix of pea gravel:turface in Los Angeles that has very low humidity and no rain in the summer. The bark and turface are moisture retentive while the grit is not. You will probably want more grit in your mix than bark or turface. But then granite gravel (poultry grit) is very heavy. Because of that many people substitute 3/8" lava rock (scoria or cinder) for the granite. That said, if you start with equal parts of the three ingredients you have listed you will be off to a good start. They get their nutrients from either a controlled release fertilizer that gets mixed in to the planting medium or from a water soluble fertilizer that gets mixed in with the irrigation water. Make sure to get a fertilizer with micronutrients as well.. No, a mister spray bottle is not right. You want to thoroughly wet the container medium by watering until water comes pouring out the bottom of the pot. Read this link for information about container media. Here is a link that might be useful: Container media

You can *significantly* cut down on evaporation by "plasticulturing" your container. Ie: you put a plastic liner (ie: a bag) over top and plant your plants through them. Helps keep the water in the soil, not the air. Unscientific experiment (tomatoes in 5gal paint bucket, +28C out, balcony, southern view). No plastic: water every other day, container weighs very little. 1 white plastic grocery bag on top: water every 5th day. Lots of ways other than plastic film, plastic is ugly after all, but none are as thin. From the pictures I would think herbs, strawberries, etc. with small roots would be okay. Tomatoes not a chance. I was at Costco the other day and they had raised bed planters. I didn't measure, but the soil depth looked about 10-12" (tapering to a point, so perhaps as shallow as 8") One issue on a balcony: when you water the person on the 1st floor will get all the run-off splashing onto their legs when you water. Water collection keeps you a nice neighbour.