Do Liners at the Bottom of Raised Beds Help or Hinder?

Q. I'm setting up some raised beds for planting this spring and wondered about water evaporation from the soil. Since water retention in the soils here in Vegas is an issue due to the heat would it make sense to put a liner in the beds to help keep the moisture from draining out so quickly?

A. No, I would not do that. Water will drain to the liner and begin to puddle or “perch”. You need continuous movement of water through the soil to prevent your raised bed from staying too wet above the liner.

Raised bed under construction with cement side walls against a block wall.

            In the Las Vegas Valley, water originating from the Colorado River carries significant amounts of salt. Our soils also contain large amounts of salts. Some are good salts and some are not but regardless we must keep these salts moving through our soils.

            The best way to do this is to “overwater” our soils to flush salts through the soil. The overwatering does not have to be much, maybe 15 to 20%. But this 15 to 20% has to go somewhere.

            To keep these salts moving or eliminated from our soils we have to make sure water leaves raised beds and goes somewhere. A liner at the bottom of the bed slows down this “flushing” action.

            If you are going to put some sort of barrier at the bottom make it porous so water can move through it.