Rain gardens are meant to help catch the rain and retain it on one's land rather than letting it run down driveways and into street gutters and such. Basically, slowing down the flow of water enough so that it can percolate into the ground. So yes, they can be dry between rains, particularly in arid climates.
Also, truck DOES grow in truck gardens! "Truck" is an old noun basically meaning "garden produce (usually vegetables) grown for market."
.....and there's your nerdy fact for the day!
