I had purchased two small concrete mixing pans to plant stuff in. Had dirt in them also which was dumped. I taped over the holes in one and use it for a mixing pan for the potting mix when I add the water saving crystals or potting mix with black cow and ironite. Five gallons of potting mix fit quite nicely in a pan.
The other pan is in the garage with holes in it. The pans are about two feet by three feet and about six inches deep. I was thinking of building a box around the pan and have the top lip of the pan rest on the sides of the box. Will put a few one by twos for a base to hold the bottom of the pan. When I am done with that I will use it for planting varieties of lettuce in it. Should be able to fit quite a few plants in it. Will space planting about every two or three weeks. A head of leafy lettuce from the store lasts me about a week. Might even plant some fresh herbs on one end.
For the space size of a container I like to use maximum production type plants. Tomatoes, peppers and squash produce quite a bit from a healthy plant. If I planted one cabbage or cauliflower in a container I would be tying up that container which costs about $25.00 for initial setup for one meal out of it from the length of time it takes from seedling to harvest. We have a two season growing season down here so that would be two harvest per year per container. Not counting crop failures .
Seeing I have peppers, tomatoes, cukes and squash doing well so far . It is time to make some vegetable chimneys. I will call them chimneys rather than cages. Cages sound like I am putting the vegetables in prison. Can not treat them to harshly you knoowww.
For the chimneys I do not like the looks of the wire hoop spacing in the store bough ones. I am going to use concrete wire and make my own chimneys with about a twelve inch diameter and to the height required for each plant. Have room to put a hand in and if necessary I can run wire diameter wise for support. Cut the wire to have legs that go in the container for support.
Another advantage to using steel wire is that it rusts. With the wire legs rusting below the potting mix the iron in the rust will leech into the mix. The rusting above the potting mix will wash down into the potting mix when it rains or by hand watering. That may solve some of the iron deficiency.