Question
I want to build raised beds in my greenhouse for organics. I need info on safe building materials that will contain compost and not leach toxins into plants. It would be nice if they lasted years as well. Thanks for any info, Bruce

Answer
You could build a small cement retaining wall, use bricks, make a stone or rock wall, a rubble/stone wall using forms, or even cinderblocks would be ok.  You could also use plastic or metal.  Anything but cedar wood, treated wood, or railroad ties would be ok, these will leach out toxins. We used old bricks in our greenhouse, and just stacked them three high on their sides and they are working well.