I made a completely portable garden that is self-watering. Each container has a water reservoir in the bottom that keeps the soil moist, and there's also a hole so excess water will drain out.
Tidy Cat kitty litter container (38 lb size)
4" perforated corrugated drainage pipe
1-1/2" PVC pipe
Step 1: Create a Water Reservoir
Cut a piece of 4" perforated corrugated drainage tile to length to fit the length of the container.
Cut a square notch in one end to fit the 1-1/2" PVC pipe
Step 2: Drill Overflow Hole
Drill a hole through the side, 4" from the bottom.
Step 3: Cut the Fill Tube
Cut the 1-1/2" PVC to length
Step 4: Assembly Time
Put the parts together as shown, add dirt, start planting!
Step 5: Watering
Add water via the fill tube until water flows out the overflow hole.