Here is another trick...

At time of potting a plant in a container, Lace several natural fibre ropes thru the Pot and leave a pigtail hanging outside of it.

Since the rope wicks water the plants roots will attach themselves to the rope. the pot never gets over watered, and in fact only the rope needs to hang into the water.
So for vacation just leave them hanging into a pond, bathtub, pool, bucket, or even a toilet tank (automatic self watering then.

I've done this technique to good success for shrubs planted along a parking lot or driveway - the rope collects the runoff, and except for the high heat of summer, doesn't need watering.

And if you enclose the exterior pigtail in a tube the pot itself can be more than several feet away.

The problem I think with the Earth box plan is that you can't really see the water level, and if overfilled the plants roots are sitting in it. Tweet