Raised Bed Evolution

Living a few miles west of Austin, Tx means the soil around here merely exists to keep the limestone rocks from bumping into each other. The soil itself is sticky clay when wet and kiln fired ceramic when dry. Gardeners have few choices - gardening in pots, hydroponics, raised beds, heavy amendment of the existing soil or just faking it and going to the farmer's market every weekend. I have tried all but the hydroponics for my fresh vegetables and am currently using the raised bed and farmer's market options.

My first design decision for raised beds was what materials to use. Many online raised bed resources seemed to be from areas where you could run down to the local sawmill and pick up 1" X 12" planks of rot resistant lumber for cheap since you could sort through the "seconds" pile. Then you would need to buy $15-$25 corner brackets from their convenient website.

Of course railroad ties and treated lumber were out unless you wanted to risk growing a third eye or develop a horrible debilitating disease from the chemicals that were supposed to leach out of the wood into your soil. Since those health issues are not without scientific basis I wanted a more benign material to hold up my dirt.

Concrete blocks are also suggested as raised bed materials.The soil around here is pretty alkaline already and I wonder if that would make pH control more difficult. Anyone have some related information? To be self supporting the blocks would likely need to be the 8 x 8 x 16 blocks in a double high row. An advantage would be they could be easily rearranged for different garden bed needs.

In my case I had about an 16' x 24' garden space. The goal was to have 5 bed rows of three foot widths across the 24' direction due to sun position. A wheelbarrow needed to fit between the beds. Using the blocks each 3 foot bed was going to need 70 inches of width! Since this was not a government project I didn't want to waste almost 50% of the available space. The concrete blocks would eat an entire row, leaving me with just 4 rows.

Being a cheap frugal manufacturing engineer I had a eureka moment as I was buying some replacement pickets for my cedar privacy fence. The cedar pickets come in handy 6" widths and 6' or 8' lengths and go for around $2.20 or $3.20 respectively. My ultimate bed turned out to be a 3' x 3' square that is 12" tall. Four pickets cut in half and 4 corner pieces made of 2"x 2" rough cedar held together with coated deck screws made a very light and sturdy bed frame.

I tried bigger frames ( 3' x 8' ) the 1st year but they required reinforcement to keep the dirt from pushing them out in the middle and were much more awkward to build. I also realized that the height meant you couldn't step over them and you had to go all the way around the row to get to the other side. The 3' squares now have a stepping space in between them so access is very easy. Maintenance will also be pretty simple since I can just unscrew any damaged board on any side and replace it in situ. The oldest 3' x3' frame is on its third year with no board damage yet. The ends of the bigger frames that were butted together had noticeable damage since they stayed damp for a long time.

The photo above shows 3 iterations of the design. The top left row shows the 3' x 8' frames butted up end to end. The bottom right row shows some 3' x 4' frames. The middle row is the final 3' x 3' design. It turned out that anything over 3' would flex and require additional support. The economics of only using 6' pickets was also a factor.

The photo above is one of the 3' x 3' frames. They only weighed a few pounds made out of the cedar. The boards were hand picked from Home Depot's pallet in order to get straight pickets with few knots and splits. The material cost was $10-$11 including screws.

I'd be interested in hearing about other frame designs that folks have used for their raised beds.