What Wood Is Not Okay For Building Garden Boxes?

Want to know the best wood for raised garden beds? Raised beds are garden containers, commonly made from wood, and the type of wood we use will determine how long-lasting, safe, and sustainable they are.

If you are looking for designs, I have free plans for building raised garden beds here .

Choosing Wood for Raised Beds

You've got perfect soil, a level yard, consistent rainfall, and everything grows beautifully, right?

Ok. No.

Every garden has challenges and raised beds can resolve many of them.

Bad soil, a sloping yard, and tree roots are all reasons to grow in raised garden boxes.

A raised growing space is also better for back and knee problems.

But what kind of wood should you use? Are some types of wood harmful for the garden?

Wood is a popular choice for building plant boxes because it's fairly inexpensive, readily available, and lasts quite a few years. But you do have to choose carefully to avoid contaminating the soil and ensure your choice is eco-friendly source, affordable, and long-lasting.

So, unless you live in termite territory, it's time to go wood shopping.

What is the Best Wood for Raised Garden Beds?
- What to Consider
  - Local & Sustainable
  - FSC Certified
  - Safety
  - Durability & Rot Resistance
Wood Options
Wood to Avoid
Wood Alternatives for Building Raised Beds
Resources

What is the Best Wood for Raised Garden Beds?

Here are the key traits to look for, then we'll explore the details.

Locally-sourced & Sustainable
Safe for soil/food crops

FSC-certified
Rot–resistant / Long-Lasting

For me, locally-sourced, FSC-certified, untreated, rot-resistant wood makes the most sense. But it is not always possible to check all these boxes.

I currently use 1″ untreated pine boards because they are readily available in my area. The wood gets a lovely, rustic barn board patina after just one season.

I also use some pressure-treated wood for various garden structures including large raised beds.

The wood that people worry about leaching 'chemicals' into the soil is CCA (Chromated copper arsenate) pressure-treated wood or old railway ties. This type of treated wood was banned years ago for household use. You can read more about it below.

Keep in mind that wood selections vary greatly by region. I admit the suggestions (below) are quite idealistic, but why not do what's best for the health of your garden and the environment if you can?

What to Consider

1 Local & Sustainable

The best choice (and often the lowest cost) is locally-sourced wood coming from sustainably-managed tree farms (as opposed to decimating old-growth forest by clear-cutting).

2 FSC Certified

If you can, use wood withFSC (Forest Stewardship Council) certification. The FSC is an international, not for-profit organization that promotes the responsible management of forests.

3 Safety Considerations

Treated Lumber

If you want to use treated lumber, do your homework first so you're certain it's safe for yourfood garden: not just fence posts and decks.

Safety standards and regulations vary by region. I notice some manufacturers now specifically mention if they consider their treated wood safe for vegetable gardens. It's up to you to do some research to decide if you trust them.

What goes in your soil goes in the water, plants, and wildlife, so it's important to be careful.

Some Current Wood Treatment Methods:

Alkaline Copper Quaternary (ACQ)
Copper Azole (CA)
Micronized Copper Quaternary (MCQ)
Sodium Borate (SBX)

TIP: To be cautious, some gardeners line their treated wood beds with aprotective layer of plastic to form a barrier between the wood and soil. Again, you will need to research the plastic to ensure it is food safe and consider the effects of condensation forming between the plastic and the wood.

CCA Wood

Do not use CCA (Chromated copper arsenate) pressure-treated wood or old railway ties. This method of preserving wood was voluntarily discontinued in the production of residential woods in the United States (2003) and Canada (2004), but it is still used for industrial purposes. The concern isarsenate leaching into the soil and uptake by plants. As thrifty gardeners, we like to repurpose wood that seems to be in good condition, but this is not an option with old, treated wood.

Read more:

Staying Safe Around Treated Wood | Government of Canada

4 Durability and Rot-Resistance

How long any wood lasts will depend entirely on the type of wood and local conditions.

My current raised beds are made from 1″ untreated pine and last approximately 10 years. But I also live somewhere where the rain is moderate and the drainage is very good.

If your raised beds will be exposed to a lot of moisture, wood like pine may only last a few years. Wood borers like termites are also a possible concern.

Other naturally rot-resistant woods (listed below) will last even longer.

Wood Options

Check before you buy to be sure the wood meets your criteria. Here's a few popular ones:

Naturally Rot-Resistant and Long-Lasting

Cedar
Juniper (rustic-looking)
Redwood
Yew
Catalpa
Chestnut
Cypress
Douglas fir
Hemlock
Pine
Spruce

Dense Woods

Black locust
Black walnut
White oak

There are more: feel free to email me with good recommendations from your area.

Wood to Avoid

Do your research first to confirm you are comfortable with the exact product you are using.

Recycled or reclaimed wood if you do not know the origin or wood that has been stained or painted. Older paints with lead are a big concern.
Older (CCA) pressure-treated wood, which is banned in several countries. ACQ (Alkaline Copper Quaternary) lumber is a better alternative.

Wood Alternatives for Building Raised Beds

As with any building materials, you must do your own research to make sure the choices you make are safe, eco-friendly, sustainable, and right for your situation.

These are ideas to explore, not recommendations.

Recycled composite plastic lumber
Composite lumber—made from recycled wood shavings.
Concrete, concrete blocks or bricks—can get quite hot in the sun, but lot of people use them with good results.
Rocks
Metal stock tanks —can rust over time.
Galvanized culvert or stock tank—may heat the soil too much.
Steel –not sure if this is food safe.
Felled logs
Old doors—cut lengthwise – be cautious with any paints or stains.
Shutters—be cautious with any paints or stains.
Straw bales

Avoid

Cinder Blocks Versus Concrete Blocks

Cinder blocks (popular many years ago) are made from fly ash and contain heavy metals. These are not considered safe for gardens.

Concrete blocks are generally considered fine but always check what the product is made from to be sure.

These all have safety concerns:

Cinder blocks
Railway ties | Creosote-soaked ones are not safe.
Tires | I know this is fairly popular but I am not convinced it is a soil-safe idea.
Paints, stains, finishes | Check with the manufacturer first.

Resources

Free Tip Sheet

My Raised Bed With Privacy Walls

Also see DIY Raised Garden Bed With Built-In Privacy Wall.

Frugal Building Tip

Design your raised bed based on available lumber sizes to minimize waste cuts.

I like to use 8-foot lengths to create easy-to-assemble 4×8-foot boxes but also keep in mind what fits your body size for easy reaching.

Free Building Plans

Free Plans for Building Raised Garden Beds
Also check your local library.

Save On Soil

Tall raised beds hold a lot of soil and that can be expensive. Use these tips for alternate ways to fill a raised bed without spending a fortune.

Recommended Book

The Raised Bed Revolution by Tara Nolan

I hope you've found this helpful.

~Melissa the Empress of Dirt ♛

Wooden raised garden beds.