Hello - I have 8 4'x4' raised bed gardens running down the south side of my house. I am planning to do a lot of work out there soon, including building a frame to replace the current 2x10s with cement walls. We'll eventually paint the cement, and I'm going to lay pea gravel paths between them to keep it low maintenance. So here are my questions:

1. How thick do you think the walls should be? My brother and husband are saying they need to be at least 4" thick. The walls are going to be 12" from ground level, but we're going to dig a trench so they're actually 18" high with 6" buried. I suspect that brother and husband agreed on a random number, and I really don't want them that thick if it's not necessary, because it will eat into my space. In fact, if my measurements are correct, I'll only be able to have 7 gardens, instead of 8! :-(

2. One of our children is autistic, which is why the pea gravel paths will be so nice. I don't get hours out there, because he is a very high maintenance child. I was reading that portland cement has aluminum in it - is that correct? I am a little concerned about heavy metals leaching into the soil, particularly because we have worked so hard to get the heavy metals out of our son. Is there another alternative that does not contain lead/mercury/aluminum/copper/tin?

I'm very excited about this project, and I want to get started building the frame ASAP. I'm going to call the hardware store and see what they say about the thickness of the cement as well, but I wanted to talk to people who have actually done something like this first. I was thinking that 2" thick walls would be sufficient.

Thanks,

Miss Info