I grew 5-6 foot tall bushes in 15 gallon pots last summer. Using them again this year since I was pleased with last summer's results.
Last year's Pokey Doke from AfterThought pictured here.
As you can see I placed the pots in trash can tops to retain some water for bottom feeding.
The biggest drawback I found was achieving even watering from the top of the pot. Water wanted to seep down about half way and come out the sides when started at the top. Watering the top then filling the trashcan top to the edge solved that problem.
Moss/algae on the outside never caused any negative issues that I could see.
Last year's Pokey Doke from AfterThought pictured here.
As you can see I placed the pots in trash can tops to retain some water for bottom feeding.
The biggest drawback I found was achieving even watering from the top of the pot. Water wanted to seep down about half way and come out the sides when started at the top. Watering the top then filling the trashcan top to the edge solved that problem.
Moss/algae on the outside never caused any negative issues that I could see.