Raised garden beds are a popular choice for many gardeners. Raised beds can eliminate problems from poor-quality native soils, help with drainage issues and increase accessibility. The most popular choice of building material for framed raised beds is wood. It is low cost (compared to permanent building materials like concrete block) and is easily purchased at home improvement stores. However, wood is prone to decay because it is biodegradable. Raised beds often stay wet year-round due to irrigation and rain, which speeds up wood decay.
The type of wood used for raised beds makes a difference. Redwood and cedar are more expensive but resist decay, so they last longer. Pine and fir will break down more quickly but are available at a fraction of the cost. Pressure-treated wood is also an economical option for improving the life of raised garden beds. However, some gardeners have concerns about the potential for the chemicals used to preserve the wood to contaminate the soil and plants.
Treated wood is very common in construction projects like decks, fences, and retaining walls. But is it safe to use treated lumber for raised garden beds where you’ll be growing vegetables and fruits? This is a controversial topic without a simple yes or no answer. In this article, we’ll dig into the details to help you make an informed decision for your garden.
A Brief History of Treated Wood
The purpose of treating wood is to help it resist rot, fungal growth, and insect damage so it lasts much longer outdoors The wood treatment process forces chemical preservatives deep into the wood under high pressure
For decades, the standard preservative for residential treated wood was chromated copper arsenate (CCA). CCA contains arsenic, which is highly toxic Studies found that arsenic could leach from CCA treated wood into surrounding soil over time
This raised concerns about health risks, especially for gardeners growing food. Eating or touching soil and plants contaminated with arsenic can pose a danger.
So in the early 2000s, manufacturers voluntarily phased out CCA for residential uses. It was replaced by preservatives containing copper rather than arsenic. The most common are alkaline copper quaternary (ACQ) and copper azole (CA).
Today, lumber labeled as “pressure treated” no longer contains arsenic. The new copper-based preservatives are considered much safer for residential use.
However, it’s important to note that CCA treated wood does still exist in many older structures. Always check the age and treatment history before reusing wood for garden projects.
Potential Safety Issues with Treated Wood
While the newer copper-based treatments are a big improvement, some potential safety issues remain:
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Trace levels of toxic preservatives can leach out over time – Studies have detected small amounts of copper, chromium, and arsenic in surrounding soil. More research is needed on long-term leaching.
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Breathing sawdust may pose a risk – Precautions should be taken to avoid breathing dust when cutting, sanding, or constructing with treated wood. Wear a safety mask.
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Some elevated copper levels have been found in plants – But plant uptake has been minimal in most studies, and no increase in vegetables.
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May not meet organic standards – If growing food commercially for the organic market, check certifier’s guidelines. Some don’t allow treated wood.
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Can be harmful if burned – Never burn treated wood, as toxic compounds may be released. Dispose of properly.
While these aren’t reasons to completely avoid treated wood for gardens, they are important factors to be aware of. Weigh the risks and benefits for your individual situation.
Tips for Safe Use of Treated Wood
If you decide to use treated lumber for raised beds or other garden projects, here are some tips for minimizing any potential risks:
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Allow wood to weather and leach for 3-6 months before using for growing food. Keep it outdoors with a plastic cover, not in the garden.
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Use gloves and dust mask when handling, cutting, or constructing with treated wood. Avoid breathing sawdust.
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Line beds with landscape fabric or plastic sheeting to create a barrier between soil and wood.
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Mulch over soil along edges of beds to reduce dust and soil splashing onto wood.
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Wash and peel root crops and low-growing vegetables that may contact surrounding soil.
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Maintain good soil fertility and organic matter levels to help bind metals. pH between 6-7 is ideal.
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Test garden soil every few years for copper and arsenic levels. A lab can determine safe levels.
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Don’t use treated wood near ponds or waterways. Copper is toxic to fish and aquatic life.
Alternatives to Treated Lumber
For gardeners wanting to avoid treated wood entirely, what are some good alternatives that will be durable outside? Here are a few options:
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Cedar, redwood, or pine – These rot-resistant woods may last 5-10 years untreated depending on climate. Cedar is the longest lasting.
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Naturally decay-resistant hardwoods – Black locust, osage orange, chestnut and white oak are good choices. Can last 10-15 years.
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Plastic lumber – Made from recycled plastic bags and containers. Won’t rot or leach chemicals. Can be expensive.
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Steel, concrete, stone – Masonry materials won’t decay and should be safe. Heavyweight though.
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Logs or whole timbers – Using uncut logs avoids treated lumber. Affordable but will eventually rot.
No material is perfect. Untreated wood needs replacing more often. Plastic, steel and masonry cost more upfront. Overall, natural rot-resistant woods like cedar and locust provide the best balance of safety, durability and affordability in my opinion.
Gardeners must weigh the potential (but low) risks of using treated lumber against the benefits like cost, widespread availability, and longevity without rotting. My advice is to take sensible precautions and not be unnecessarily alarmed about using treated wood. Just be sure to use the newer copper-based treatments, not old CCA wood.
The tiny amounts of chemicals that may leach into soil are likely less than what’s absorbed from pressure-treated decks or fences nearby. While not zero risk, treated lumber seems relatively safe if used properly. But alternatives like cedar or plastic lumber fully eliminate the risk for maximum peace of mind.
I suggest evaluating your specific situation and comfort level with risk vs. effort and cost. An extra barrier liner provides added protection too. With sensible precautions, treated lumber is a viable option for many raised bed gardens.
OSU researchers study leaching
Many gardeners are hesitant to use pressure-treated wood for raised beds. The information available through web resources is often conflicting, and much of the information available on web pages and blogs is not supported by research.
Oregon State University researchers began conducting a study in 2021 to answer two common questions:
- Do raised beds constructed from pressure treated wood leach copper into the soil?
- If leaching does happen, do the vegetables and herbs grown in the raised bed absorb the copper?
What about arsenic warnings?
When researching this topic, you may come across warnings not to use pressure-treated wood due to the presence of arsenic. It has been over 20 years since the arsenic-containing wood preservative chromated copper arsenate was used for wood available to the general public.
Reusing or salvaging lumber that is over 20 years old may risk introducing CCA-treated lumber into your garden. While there is no evidence that the use of CCA-treated lumber increases the risk of arsenic leaching and accumulation in vegetables, manufacturers do not recommend it for this application. It is also not recommended that gardeners use old railroad ties for garden boxes. The industrial preservatives used in railroad ties are not intended for garden or residential use.
Wooden Garden Boxes: The Ultimate Guide to Choosing the Best Wood Species for Raised Bed Planters
FAQ
Can you use treated wood for garden beds?
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Older treatments are not safe:Avoid using older pressure-treated wood containing arsenic (CCA) as it can be toxic.
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Check for “ground contact” label:Ensure the treated wood you buy is specifically labeled as suitable for ground contact.
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Minimal leaching:Studies show that the amount of chemicals leaching from modern treated wood into the soil is minimal and not considered a significant health risk.
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Alternative options:If you are concerned about any potential chemical leaching, opt for naturally rot-resistant woods like cedar or redwood.
What wood should not be used in a raised garden bed?
Just about any wood is fine except black walnut as it has a toxin the suppresses plant growth.
What kind of wood should you use for a raised garden bed?
The Best Types of Wood for Raised Beds It’s best to use untreated wood to build your raised garden beds, preferably a type of wood that won’t decay quickly, such as cedar, redwood, or hemlock. Both the type of wood that you might find for sale and its affordability will vary based on where you live.
Where not to use pressure-treated wood?
Pressure-treated wood should not be used where it may come into direct or indirect contact with drinking water, except for uses involving incidental contact such as fresh water docks and bridges.
Is pressure treated lumber safe for raised bed gardens?
I would appreciate your opinion on this matter. The safety of pressure treated lumber for raised bed gardens has been examined by several researchers. From what I’ve seen, the consensus is that the chemicals do leach out of the wood into the soil and are uptaken by the plants in very small amounts.
Which Wood is best for a raised bed?
If you can find it, its hardiness makes it a good candidate for your raised beds (source). Pine is by far the easiest wood to find and one of the least expensive. Pine is strong and easy to use, which makes it a popular choice in a variety of building projects, including raised beds. However, pine is not very resistant to rot, decay, and insects.
Can you grow food in a treated wood bed?
Based on wood treatment, growing food in beds made of treated wood is unsafe as safety has not been established. Get away from treated wood in the garden, including railway sleepers, as the ones available may have been soaked in creosote, and you don’t even want to know what’s in it.
Is reclaimed wood good for garden beds?
The reclaimed wood from electricity and utility poles is another affordable option for DIY projects. However, it is also treated with a lot of harsh chemicals. This does make it last a lot longer outdoors, but it also makes it dangerous for plants. What are Some Alternative Material Options for Building Raised Garden Beds?
Can you use pressure treated lumber in a vegetable garden?
Yes. It is possible to find pressure-treated lumber that is safe for use even in a vegetable garden! Depending on your needs, budget, and growing zone, this may be a good option for you to consider. The purpose of pressure-treating lumber is to make it more resistant to rot and decay.
Can I use 2×6 lumber for a small raised bed?
I am considering using some 2×6 inch material for a small raised bed for strawberries. My first thought was to consider pressure treated lumber, but I have read conflicting articles on the the safety of this product, with the chemicals possibly reaching the plants. Others claim this doesn’t happen and the lumber is safe.