New wicking container garden: how deep is too deep?

I am building a new container garden made from 55 gallon drums.
Each will be plumbed to the next and the whole thing will receive rain water from a roof.
I plan on dedicating this container garden to annuals that my wife and kids like.
It's set up to be easy picking and self watering.

My current set of 55 gallon barrels have the top 1/2 to 1/3rd occupied with growing media, with an additional smaller column of wicking soil extending to the bottom of the barrel.

This time around I planned that each full barrel would have a half barrel of growing media sitting on top of it.
This would increase water storage but put the lip of  the half barrel at about 4.5 feet off the ground, as compared to roughly 3 feet off the ground.
That height isn't convenient to most people, so I'm second guessing my design.
I'm also wondering if water will readily wick that high.


I have other, adjacent uses for the half barrels, and I can redesign the full barrels to have soil in their top third, but I am itching to be done building and on to planting out these beds.

Please weigh in with your thoughts.
It helps to hear other points of view on a project I'm very into.

I made several of these "self-watering" containers in previous gardening adventures, but I used standard 5-gallon buckets because the top one nestled so well inside the bottom one and left a few inches for a water reservoir.
Could you do the same with the barrels you have, but cut the bottom one in half? Make the wicking tube reach the bottom of the bottom barrel and still reach an inch or two into the bottom of the top barrel. You have a few drainage holes in the bottom of the top barrel to allow water to seep into the lower water reservoir.
That would reduce the overall height by about 1/3-1/2.

I also made beds with wicking system of 55-gallon barrel, and I can say that the water does not always rise well above 30-35 cm layer of soil, especially if the ground is not very loose. When the layer is too thick, the top dries faster and the bottom may be raw, but plants do not use this. I would advise not to make a layer of soil above 1/3 barrel, otherwise it will be inconvenient to work and the moisture is distributed worse.

Another idea about that wicking soil tube/container.
Instead of using the mesh, which I think is likely to lose soil, use a PVC pipe with several 1/4" holes drilled in it.
That's what I used in all of my water reservoir containers, and they worked really well. A 2" PVC pipe fits snugly in a 2-1/2" hole.

It took me a while to find these documents I made on building a water-reservoir container.
I thought I would post them here if anyone has any interest and it might be of use to you in your modification attempts.

So I took the suggestions here and built out the barrels.

I used old pizza screens over plastic mesh from some bread trays, so my barrel beds could air prune any tap roots.
I hope to use the to start tree seedlings and perennial cuttings alongside the annual vegetables.

I think I see what you have done there.
What does the stack look like now?

Well, I'll have to take a photo of a filled container later, when I get home, but this is with one of two dishpans of peat added
This first panfull fills the 4" PVC and spills over a little, the second covers all of the mesh.
I topped it with raised bed soil that is primarily leaf mold.
I know the peat will wick, I'm not sure about the raised bed soil.
One good thing about building them this way is less soil overall, making changes easier.

Here is a finished barrel with some projects planted out in in it: