I have a portable 12 volt hand drill. I use the bits you use to bore holes in wood (1/2 inch wide). I put a few holes in the bottom and some in the sides about an inch up on the sides. I figure if they don't drain well in the bottom that some of the water will drain out the sides. I use pine bark nuggets in the bottom. I fill it about 1/3 full. Someone told me that tropical milkweeds like acid. I figured that the pine bark would do the trick and also saves on soil.
With all those large plastic containers that I had planted last year, I did not have to go wrangling once for milkweed. Now, many of the places that I would have gone have been destroyed.
Herndon, VA (USA)
Take care of the small things....