Is It Safe to Use Pressure Treated Lumber in the Vegetable Garden?
Is it safe to use pressure-treated lumber in the vegetable garden?
This question came up last night when I was a guest on Mike the Vegetable Gardener’s Show, which will air on YouTube in about a week. Here is the link to the channel. My show will on next week. We talked about raised bed vegetable gardening in conjunction with my book, Plan and Build a Raised Bed Vegetable Garden. Of course, the topic of pressure treated lumber came up.
Here’s the latest research on why it’s probably okay to use pressure treated lumber for a raised bed vegetable garden.
Pressure Treated Lumber: Is It OK to Use in the Garden?
Pressure treated lumber sold in stores today is different from that you probably knew many years ago. In 2002, the Environmental Protection Agency worked to outlaw the use of chromate copper arsenate (CCA) from lumber for home use. CCA offered several benefits, including greater protection against insect damage, but a significant drawback: it leached arsenic into the soil.
Now, let’s talk about that for a minute. Arsenic, as you probably know, is poisonous. It does not hurt you in small amounts, and you probably have some in your body now just from eating conventional produce. It can, however, build up over time into amounts significant enough to cause health problems.
When CCA-treated lumber touches the soil and water drenches the wood, over time, the compound breaks down and leaches, or drips, into the soil. Plants take up nutrients through their root system. The water they drink through their roots contains minerals and nutrients. It may also include some of that arsenic if CCA lumber is used.
However, CCA was OUTLAWED in 2003. That means that companies can no longer use it to manufacture pressure-treated lumber. Instead, another compound, called alkaline copper quarternary (ACQ) has been used as a replacement for CCA. Is ACQ totally safe? There’s no consensus on its safety record, and aside from manufacturers’ tests, little has been done to truly ascertain its safety.
How Many Chemicals Get Into Vegetables Intended for Human Consumption?
That said…there have been some limited studies in garden plants to see how much CCA or ACQ actually does get into vegetables intended for consumption. I’ll link to the scientific research at the end of this article, but here’s the gist of the results from CCA-treated lumber (remember, it’s outlawed, but the amounts found in plants may be comparable, more or less, to ACQ. That assertion is not backed up by research but my own extrapolation of the data.)
- Arsenseninc, copper, and chromium levels found in the vegetables grown in raised beds made from pressure treated wood were the same as conventionally grown vegetables purchased from a grocery store.
- Romaine lettuce grown in pots with soil in which small amounts of compounds such as arsenic were also tested to see how much of the chemical would be absorbed by the plant. The Romaine lettuce absorbed some. In a 50 gram serving (considered a normal serving of lettuce for an adult), 0.004 mg of As was found. The estimated safe level of arsenic is 0.05. You would have to eat 1.3 pounds of the lettuce in the experiment EVERY DAY to exceed the safety limit.
- The closer vegetables are to the wood, the more chemicals they absorbed. About six inches away from any pressure treated wood, no trace of the chemicals used to treat the wood was detected.
- Root crops such as beets, turnips, carrots, and potatoes contained most of the metals they absorbed in the skin. Therefore, peeling removes most of it.
- Plant species differ greatly in the amount of metals they take up from the same soil. This is due to the difference in movement of fluids inside the plant itself. Most metals remain in the roots with the exception of leafy green vegetables. Lettuce, spinach, and mustard greens tend to move metals into the leaves.
The Bottom Line: You Can Use Treated Lumber for Raised Bed Gardens
The bottom line is that the majority of scientific evidence points to the relative safety of using pressure treated lumber in raised beds used for vegetable and food production.
Here’s how I look at it: there are risks from all of the food we consume. I think nothing of eating conventional products and packaged foods. I admit that although I love to cook from scratch and that I try to cook healthy meals, some nights I work too late, and it’s Hamburger Helper mix for us with a side of vegetables.
I don’t use pesticides or artificial fertilizers on my vegetables. If they are getting any chemicals from the ACQ treated lumber (the beds were built after 2009, well after the time frame in which the EPA required companies to phase out the use of CCA-treated lumber), the trace amounts should be so minor that it won’t make much of a difference to me.
For Those Who Choose Not to Use Pressure Treated Lumber: Alternatives
There are some loyal readers of this website and blog who say to themselves, “Well, that’s fine for you, Jeanne, but I won’t use any pressure treated wood in my garden, period!” If you really don’t want ANY chemicals from the soil, you do have options to build your raised beds for a vegetable garden.
Optional materials to build raised beds include:
- Untreated lumber. It’s going to break down faster than treated, but it’s inexpensive and easy to work with. Pine is inexpensive, easy to cut, and readily available.
- Cedar: A natural product and also wood, so it’s easy to work with. Cedar is naturally rot resistant. It can be expensive.
- Stone: You can stack landscape stones or bricks to make a raised bed.
What you should NEVER use for a raised bed:
- Old tires. I go a little crazy when I see all those Pinterest pins of recycling big truck tires into raised beds. Sure, they’re fine for flowers. Have fun with flower planters. You don’t eat flowers. But for vegetables, fruit and herbs, avoid tire gardens at all costs.
Tires pick up all sorts of crud from the road. Oil, gasoline, road salts…I’m gagging just thinking of the chemicals that are inside those tires. When you pour soil inside and water your plants, guess what? They leach out of the tires, too, and if you’re trying to grow lettuce, that Romaine lettuce is going to suck up the minerals as well as the chemicals. And you’re going to eat the lettuce and basically eat recycles oil, gasoline, and road salts (more or less). No thank you.
If you’re concerned about health and safety, save those tires for swings, pretty flower planters, or for the recycling center. They do shred them into nice materials to create pavement, horse riding ring footing, and many other items that are useful and don’t end up in the landfill.
(Shameless plug for my book)
Raised Bed Vegetable Gardening Research
I hope that this has helped clear up some of the confusion around using pressure treated lumber in a raised bed garden. Here is the research I’ve read to write this article. Feel free to link to it or to share it with friends.
- National Pesticide Information Center
- Oregon State University Extension Service
- Pennsylvania State University Research and Extension Office (PDF download)