Garden Box Floor:
I've been using my garden boxes for about 15 or 16 years. The original boxes were built by my nieces and nephews and were made out of hardwood that was donated by a lumber company. They were patterned after the ones that Craig hospital, which were made out of concrete and were solid top to bottom. When building mine, they copied this pattern. We had to drive all over to get rocks and stones to fill the majority of the box prior to the top soil. They were difficult to work because I always had to be sideways. I couldn't believe the speed at which the hardwood rotted. They only lasted a few years.
My son Mark and I decided to create new ones. The pattern we used can be seen on Garden Box Plans. Mark built them out of pressure-treated lumber and they had 3/4" exterior plywood floors. Almost every year we need to add top soil. After many years the floors finally began sagging and delaminating from the weight and water. Mark replaced one of the flower boxes a few years ago and put in a 2 x 4"floor, but that he feels is not strong enough because the vegetable boxes have more soil in them.
Mark, who is a structural engineer, and I talked about building completely new boxes open on all sides, but decided the time and cost made it a foolish idea. Mark believes the best option is to use two pieces of 3/4" exterior plywood changing the direction of the lamination so the grain is running opposite from each other. Plywood is made by gluing thin sheets of wood together with the gain of each sheet running in opposite directions. Because of the lamination process, plywood is incredibly strong and he feels is better than using 2" thick standard lumber.
Mark began by removing one side of the box. He and my grandson Tyler began removing the dirt from the box with shovels. The dirt filled two wheelbarrows and a plastic sled. We were all amazed at what great shape the wood was in. There was no rotting on any of the frame. When the box was empty the remaining sides were removed and the plywood bottom was taken off. In the picture below you can see Mark replacing the old piece of plywood with two new ones. The sides were put back together, placed on the plywood and screwed back together. A few drainage holes were drilled through the bottom and then Tyler and Katie shoveled dirt back into the vegetable box. The entire process was a lot easier and took place quicker than we had anticipated.
Thanks to my son and grandchildren Tyler and Katie for enabling me to continue with the lifestyle I love.