The main difference between the 18 gallon containers and the 5 gallon containers is moisture management. I can water the larger containers a lot less and therefore worry less about a complete soil dry out.
It is important to amend your container soil yearly. Tomatoes literally suck the life out of container soil mixes. There is no exact amending recipe but I show you my basic routine in the video. You want to add organic matter, some fertilizer and calcium (egg shells). Adding calcium to your soil helps prevent blossom end-rot from affecting your tomatoes.
The video covers these concepts. Enjoy!
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