Question
Hi Frank & Vickey    I live in Southern California and want to have raised garden beds for my backyard.  I have priced wood and WOW its expensive so I started to research River Rock (I have tons of it in my yard and enough to do several 2x4x8 beds)  My question is to verify I use larger rocks on the bottom, and use small and large ones in the walls and top (mine range from football size to small beach ball size)  Will I need a foundation or can I dig a little trench and start putting them in?  Also would you suggest I use mortar? Is it toxic to my vegetables?  Or do you think stacking will be just fine? I prefer to try and stack them if possible........... If you suggest mortar can you tell me a little more about it.  I have done much research but cant find much on the mortar.  Thank you very much for your help.  Darlene

Answer
We just dig a little trench and start.  River rock is usually not real flat, so you would probably need to use cement because they would be hard to stack.  

But if they are really flat sided then you could just dry stack them. Large ones one the bottom and smaller ones toward the top. Usually we dry stack with cement/rubble behind the rocks as we go up to hold them in place, and to make an area of cement/rubble as wide as the bottom rocks or at least wide enough to make a flat top about 6-8 inches wide.  Then it looks nice and you can sit to garden.

You also could make a plywood form, (plywood rectangles), one for the length and one for the width of the beds, place the rocks flat against it on the inside front, pour in the cement/rubble mix, work your way up to the top of the form, and top off the cement with rocks on the top (when it has set up enough so they don't just sink into the cement.) Then when you take the forms off you have a wall with the rocks imbedded in it.

You can buy a pre-mixed Portland cement (it is the proper mix of sand and cement) just add water.  Cement is not toxic to plants.  You can also buy a load of cement sand and bags of Portland cement and mix it yourself. One cement to three sand.  Measure it with a "piled as high as possible on a square shovel" method and put it into a wheelbarrow. Then you add a little water and mix it until it is like really thick pea soup.  Let it set 5 minutes or so and begin using it.  This is the hardest part, the consistency, so start with a small batch until you get the idea.  A plastic wheelbarrow is best(no scraping noises, easier to clean, and lighter) and a flat garden hoe is the best mixing tool.  Just go back and forth until it is well mixed.

You can go to our website to see examples of rock wall construction at http://www.avant-gardening.com in one of the virtual tours.