Answer: Here's what works for me:
Water the plants thoroughly and then place them all together in a bathtub (so as the water evaporates from the containers, it will increase the humidity around all the plants). Then up-end a pint sized bottle of water in each pot, burying the neck of the bottle into the soil. As the potting soil begins to dry out it will wick water from the bottle. If the container is really large (3-5 gallon) you might want to use two water bottles per container.
Works for me!
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