Good, Safe Choices for Raised Beds
People often ask me what they can use to make raised beds and these galvanized troughs are the first thing that come to mind. Relatively inexpensive ($89 for a 4′ x 2′ x 2′ tank) and durable, livestock tanks make it possible for gardeners to create raised beds quickly and easily.
We got ours because we’d like to grow vegetables and herbs free from pee—and worse—and our lie that the backyard kitchen garden has an electrified fence around it no longer fools our dog, Lily. Troughs are also a great solution if you’ve got poor soil and you don’t want to have to amend a large area. Wall-to-wall cement outside your apartment? No problem. Plop a galvanized tank down, drill some holes in the bottom and you’ve got yourself a garden.
Drilling the holes is the only time-consuming part of this project, really. For a tank that’s four feet wide, two feet deep and two feet tall you’ll need to drill about 8 – 10 holes and I’d suggest removing the drain plug too. We got our tank at a place called Tractor Supply Company, but Fleet Farm and other farm supply stores carry them for reasonable prices too.
I want to say, too, that I know there has been concern over galvanized troughs leaching zinc into the soil. After doing quite a bit of research, I feel comfortable that this isn’t a serious problem. To keep zinc leaching to a minimum, though, it’s best to strive for a neutral pH level so I will test the soil each season to be sure all is well.
If you don’t like the look of cattle troughs, and I’m sure they are not loved by all, there are other good options such as: cedar, natural stone, pavers or even landscape block. What you don’t want to use is treated lumber.
Though there is no simple answer to the question of whether it is safe to use treated lumber to build raised beds for edibles. As you probably know, the Environmental Protection Agency (EPA) banned the residential use of wood treated with chromated copper arsenate (CCA) back in 2003 over concerns that arsenic could be leaching out of the wood and into the soil in harmful amounts. That arsenic-treated wood was replaced with another type of wood known as ACQ, which is named for the chemicals it is treated with—alkaline copper quat. (Quat is a fungicide used to keep soil fungus that harms the wood at bay.)
While it’s true that ACQ is free of arsenic, studies have shown that it does leach some copper. Whether or not this copper leaching is a safety issue for food crops is unknown and continually discussed. But scientists and the EPA both acknowledge that copper is toxic to aquatic life. So using ACQ anywhere near streams, ponds or storm drains that feed into waterways is not a good idea.
Does that mean it’s okay to use treated lumber if your garden is far from water? Honestly, every gardener needs to decide that for his or herself because the science is far from conclusive. Here are some things to consider. Growers of certified organic vegetables are not allowed to use treated lumber near food crops. Scientists’ opinions on ACQ are wide ranging with some dismissing copper leaching as insignificant and other asserting that, even if it is more significant, plants that take up unsafe amounts of copper would likely be long dead before we ever served them for dinner. And know this, too: Even as arsenic-treated lumber was being pulled from the residential market by the EPA after years and years of debate, some scientists were still insisting that it was safe.
I like to think I have a healthy respect for science. I appreciate research-based opinions and I often look for research to affirm what I read and hear about gardening. At the same time, I never forget that science has its flaws and shortcomings, too. I know, for example, that Monsanto employs a whole lot more scientists than, say, your average organic farmer.
As for treated lumber, I don’t feel comfortable using something around my edibles that comes with a warning label cautioning me to wear gloves when handling it. And, even if I did, the storm drains on my corner lot lead straight to Lake Harriet, so why take a chance that copper could get into the lake?