Is it me, or does it seem like all everyone is talking about right now is growing edibles in their gardens? I was out at the arboretum giving a talk on shade plants the other day and, I’m telling you, nobody cared about that topic. Oh people were polite and all, but outside the auditorium on breaks in between speakers, just about everyone who asked me a question asked about growing food.
Even on smallish urban lots, more and more people are incorporating edibles into their landscapes and, by far, the two most-asked questions were about safety. Is it safe to use water from rain barrels on edibles? And, is it OK to use treated lumber to build raised beds? Honestly, I lost count of how often I was asked both things. But that being the case, I realized I had a good column topic on my hands, so here it goes.
Using rain barrel water on edibles
As a master gardener, I’ve been taught to answer the question of whether it is safe to use water from rain barrels on edibles with a slightly squishy “no.” So far, the issue is widely debated, there isn’t much research on the topic, and there isn’t likely to be since testing is expensive and would vary so much based on location, roof type and weather conditions. Some studies have shown, though, that rain barrel water often contains runoff from roofing materials (such as asphalt), as well as chemicals found in the air, mold, fungi, bird poo and other yucky stuff.
Still, some gardeners don’t like the idea that water they’ve painstakingly collected can’t be used as efficiently as they would like. So while I don’t use rain barrel water on my edibles, if you choose to, there are some things you can do to minimize potential safety issues: (1) Water the soil around edibles without letting it come in contact with plants. (2) Rinse edibles before eating with a veggie wash as you would other produce from the store. (3) Drain your rain barrel regularly and rinse it out well if it smells murky or musty at all.
Raised beds and treated lumber
This is another hotly debated topic. And 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 OK 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? Instead, this summer, I plan to buy a couple of those oval-shaped galvanized water troughs at Fleet Farm to use as raised vegetable beds. Other options include: cedar, natural stone, pavers, even landscape block.
Meleah Maynard is a writer and Master Gardener. Email her a question or read her weekly gardening updates at her blog: everydaygardener.com.