I live on a small urban lot with utility lines running underground all around. This is one of the reasons I garden in raised beds (other reasons are so that I can control the soil better, keeps invasive grasses out, and the height makes it easier as I get older).
Around the perimeter of my yard is an easement. There have been a few times over the years that utility companies have come in to dig up and replace their lines. Thus I am not able to put permanent garden beds there.
So my options are limited when it comes to garden expansion.
For the last couple years, I have used fabric grow bags, which seem to work well as long as I can keep them watered (I use solar drip irrigation -- more about that here). I set up some temporary platforms to put the bags on, since I wanted to be able to weed-eat around them. We have Bermuda grass that will take over anything it can reach, so having them up off the ground protects them from the invaders. Those temporary platforms worked well, but I wanted something a bit sturdier and nicer.
So I hit upon the idea of building low benches to set the bags on. Fairly easy to build, inexpensive, and sturdy. My kind of project!
They basically consist of 2 - 6 ft long 2x4s for the sides, and 7 - 1 ft pieces of 2x4 for the ends, legs, and a center brace. Screwed together, and topped with 3 - 6 ft cedar fence boards. I did use treated lumber for the 2x4s, but the cedar on top will keep the bags away from the chemicals. I plan to set them up on some paver stones to keep the legs away from the grass so they will last longer.
With my daughters help, we are able to cut and assemble a bench in about 45 minutes. Cost is between $25-$30 a bench. Not too bad for something that I hope will last years and be movable should I need to rearrange them or use them for other purposes.