Is It Safe to Use Treated Wood in Planter Boxes?

#EcoAdvice from our expert

Dear Dr. Donley,

I would like to put some raised planter boxes in my yard to grow vegetables and herbs. I was going to use pressure-treated lumber so they’d last a long time, but a friend told me it might be dangerous to grow food near treated lumber. Is it safe to use treated wood in planter boxes?

Signed,

Thyme to Turnip Some Answers

Lettuce Begin,

Wood treatment is simply meant to prevent the natural process of decomposition. Most lumber doesn’t last very long in the wet, outdoor environment, so builders often seek out wood pretreated with a pesticide that prevents fungi and insects from breaking down the wood fibers. This is referred to as “treated” or “pressure-treated” lumber, and it’s one reason many homes still remain attached to their foundations.

While treated wood has its uses, it’s important to know when not to use it. Until recently most treated wood was coated with chromated copper arsenate (CCA), which is just as bad as it sounds. Arsenic, a known carcinogen, makes up about one-fifth of the CCA mixture, and unfortunately it took us about 60 years to realize it may not be a good idea to have arsenic-coated wood in everything from outdoor play equipment to picnic tables.

In 2002, with a backward power dynamic on full display, the Environmental Protection Agency nicely asked the pesticide industry to phase out CCA. It agreed to do so — but just for residential uses. Sadly, this is just one of many examples of the EPA failing to impose complete bans on harmful toxins in favor of partial, “voluntary” bans from morally bankrupt industries. Nevertheless, the residential ban was a significant public-health victory, and there are now fewer children running around with arsenic on their hands after playing in the playground.

Since then, numerous wood treatments have been approved to replace CCA. The EPA has opted not to assess the dietary exposures from treated wood in picnic tables or planter boxes. However, some wood treatments, like copper naphthenate, specifically state on the pesticide label that they are not suitable for garden applications where fruit or vegetables will be grown.

So, depending on the wood treatment, it’s either unsafe to grow food in treated wood planters or the safety has not been determined. I’d say stay away from treated wood in the garden, and that includes railroad ties — those are soaked in creosote (and you don’t even want to know what’s in that).

But don’t fret, because you have plenty of other options available to you. You can use traditional lumber and accept that you’ll have to replace it in about 5–8 years. If you go to a construction-material recycling center, you’ll have access to an endless supply of affordable untreated wood looking for a second life.

Or, if you’re looking for something that will stand the test of time, rot-resistant wood like cedar or natural stone are two options — but they tend to be pricey and, unless you can gather stones near your home or find previously used cedar (which can be tough), are not the most environmentally friendly way to go.

Often people believe they need to build raised beds, when actually they’d be better off planting directly in the ground. But if planting directly in the ground isn’t an option for you, go to the local recycling depot or throw a party and collect a bunch of wine bottles. Bury the necks of the upside-down bottles in the ground and line them up in a rectangle, with the large base sticking out of the ground. That will give you about 10 inches of rise that you can fill with soil. If you need to, you can run a strap around the outside to prevent the bottles from bowing out over time. You may look like the neighborhood wino, but your repurposing cred will be unmatched.

Stay wild,

Dr. Donley