Note from Kirsten: Today’s DIY post is brought to you by Ken Charm. Ken works on the sales counter at our Everett location and recently got involved with Dunn DIY through the Northwest Flower & Garden Festival. (Find Dunn DIY at the 2018 Northwest Flower and Garden Festival by visiting booth #707. You can even watch me lead a live tutorial from the DIY stage!)
Ken and I got to talking about the pros and cons of various wood species in a garden setting, and it was clear to me that this was a topic of interest for him and something he had spent time learning about so he could share with others. Ken studied environmental science at Western Washington University and worked as an environmental consultant for 14 years, so he knows a thing or two! It'd be hard to find a better person to break down some of the differences between cedar, juniper, and pressure-treated lumber. Take it away, Ken!
I first met Kirsten at the 2017 Seattle Flower and Garden Show, and our conversation almost immediately went to discussing the Dunn DIY juniper planter box and how much I liked using juniper for raised garden beds. We discussed everything from its beautiful appearance of the wood to its wonderful smell, and I told her about the reading I’d been doing on how long-lasting juniper not only makes an attractive choice for a raised bed, but a practical one as well.
With that discussion in mind, Kirsten asked me to talk about the differences between juniper and cedar for building planter boxes. (I decided to add pressure-treated lumber to the mix because it’s something that I'm asked about at Dunn Lumber on a regular basis.) Ultimately, the material you use to build your raised bed is a personal choice, and this blog is just meant to give you a bit more information to confuse—I mean, help—you make an informed decision. The options are nearly limitless!
I know people who choose simple framing lumber because it’s inexpensive and lasts for years. They’re the first to say other choices are prettier, but the aesthetic of the bed isn’t their primary objective. I make raised beds clad in metal roofing material. Others use concrete, brick, empty wine bottles, or just mounded soil. What you use is up to you, and if you get enjoyment from it, I think it’s a wonderful choice.
Cedar is a commonly harvested softwood used mostly for exterior decks and siding. It’s readily available in various grades, and, in my opinion, is an attractive choice. Cedar is not a very dense wood, and while it’s softer than other conifers, it’s naturally more rot-resistant. The rot resistance is great for a raised bed, but the lower density works against it when it’s subjected to the rigors of heavy watering and high biological loads.
The Forest Research Laboratory at Oregon State University (OSU) has been testing different woods for use as fence posts since the late 1920s, and their 1996 Post Farm Report found that Western Red Cedar had a lifetime of 20-25 years. I wouldn’t expect a planter bed to last quite as long, but the findings from the OSU research are a good guide for comparing the relative longevity of different wood species. In summary, cedar is attractive, fairly stable, readily available, and should last a good long while.
In Eastern Washington and Eastern Oregon, juniper is sometimes referred to as a native invasive species. Because of fire controls, nature’s main method of managing juniper populations has been removed, and as a result, junipers are out-competing other native species. To help restore the ecosystem, juniper—like the kind Dunn Lumber carries—is harvested to control population growth.
Because the harvested trees are young, they aren’t that big around—the larger pieces of lumber have a combination of hard, dense, rot-resistant heartwood and an outer layer of soft sapwood. This means that juniper can be prone to twisting, but it also means it's extremely elastic and moldable and holds hardware such as nails, screws, and staples better than other species. Don't be fooled, though: it's still strong.
Juniper's a popular choice for its aesthetics—striking grains and warm tones—but it's most celebrated for its longevity and resistance to rot. The OSU research shows that juniper fence posts can last a very long time—up to 60 years or more—but the average lifespan (which is impressive) is in the 30-year range, closer to that of cedar.
Because harvesting juniper helps restore the Pacific Northwest’s ecosystem, you can feel good about choosing juniper. Compared to cedar, juniper holds hardware with ease, is just as attractive and long-lasting, is more elastic, and may be readily available depending on the market.
This leads us to pressure-treated lumber.
This is a sticky conversation, and I hope that you, dear reader, understand that I’m not suggesting you should or shouldn’t use a lumber you don’t feel safe using. That said, I personally feel safer than ever using pressure-treated lumber in planter boxes—even when growing fruits and vegetables—and I’ll do my best to explain why.
First, a bit about my background. I have a degree in environmental science from the Huxley College of Environmental Studies at Western Washington University. I spent 14 years as an environmental consultant before the recession of 2008 moved my employment status from full-time to project-based and I started a handyman business to make ends meet. I eventually landed at Dunn Lumber on the sales counter and remain amazed that companies actually treat their employees as wonderfully as Dunn treats me. My background—and 70 years of industry use and research—can vouch for the safety of lumber treated with CCA (chromatid copper arsenate) and CA-C (copper azole type C, which has two ingredients that are used as soil amendments and fungicide on food crops.)
One analysis by the Florida Department of Health, as cited in the Association for Challenge Course Technology, shows that "a child would have to eat a spoonful of dirt taken from right next to a CCA-treated play set every day for 30 years before there would be a potential health effect."
Arch Wood Protection, which supplies chemicals used in the pressure-treating process, backs the use of pressure-treated wood in raised gardens, too. Here's what they say: "Thousands of applications [of preserved wood in gardens], plus many laboratory studies, enable us to say with confidence that there is no cause for concern from harmful uptake of preservative ingredients into fruits or vegetables." Dunn Lumber's pressure-treated lumber is supplied by Exterior Wood, which uses Arch Wood Protection chemicals.
Another great study about using treated wood in a produce garden is a 2014 study in the European Journal of Wood and Wood Products. Their study used planter beds made of treated and non-treated woods along with the same soils and the same types of plants, and then compared copper accumulation between them. They found no statistical difference in copper accumulation between the two types of planter beds. That study made me feel better about using pressure-treated wood for a veggie planter. In fact, I recently built a raised bed in my backyard using pressure-treated wood—and one of my two pugs (pictured above) loves to get into the vegetables as they're growing—and I have no safety concerns whatsoever.
Cedar and juniper—as well as other materials—are fantastic for building raised beds, and if you feel safer using those, you absolutely should! Next to cedar and juniper, pressure-treated lumber is treated with safe chemicals that may make some feel uncomfortable, but it’s an affordable, readily available lumber that—with a lifetime warranty!—will last the longest of the three.
I loved delving deeper into the differences between these three types of lumber, and I hope this encourages you to dig even deeper into your planting beds (pun intended).