How To: Toxin-Free Raised Bed Liner

Raised garden beds are excellent to grow vegetables in, however, finding inexpensive and toxin-free materials can be a real challenge. 

I’ve been experimenting with different raised bed materials for years and have finally landed on the perfect combination of durability + low cost + non-toxic materials.

In this article, I’ll share with you my easy and fairly inexpensive method for building a raised garden bed with a durable, non-toxic liner. All of these materials can be easily found at your local building supply store.

Let’s get building!

What is a Raised Garden Bed?

A raised garden bed is a loose term to categorize any form of gardening that takes place in an elevated space rather than straight in the earth. Raised bed gardens can be constructed from felled logs to cinder blocks and lumber to galvanized steel.

A raised garden bed has many advantages:

• Easier to access plants at an elevated level
• Less weed pressure
• Looser soil with less compaction
• Improved soil quality 
• Warmer soil to extend the growing season
• Better drainage

A raised garden bed has some challenges:

• Raised bed materials can be quite expensive – Just one 8 foot cedar 2”x10” board is $86 at the time of this article, and concrete blocks are even more!
• Natural materials like logs or untreated pine boards can degrade quickly, requiring replacement every few years – see photo below of untreated pine lumber after just 3 years
• Rot-resistant materials can be toxic – pressure treated, creosote railroad ties, etc
• Raised bed materials like concrete and bricks are heavy and hard to move (and expensive!)

Don’t worry! I have a solution for all of these challenges and it includes a toxin-free raised bed liner!

Do I Need a Raised Bed Liner?

It depends on your raised bed design, but the short answer is yes. If you are using treated lumber, like what I’ll be recommending below, then you definitely do. There are many advantages to adding a liner along the inside edge of your garden bed.

Non-toxic barrier

If you are using a rot-resistant material like pressure-treated wood, then I highly recommend using a raised bed liner to keep the chemicals out of your food. Pressure-treated wood is appealing because it’s inexpensive and will last up to 10 years, unlike most types of untreated wood.

Prior to 2003, arsenic was the chemical of choice for treated lumber. No thanks! Today, the most common chemical used is alkaline copper quat (ACQ). While this is a less toxic option than arsenic, it’s still not something that I want mixing with my food.

Keeps dirt in place

If you are using logs or bricks that don’t seal your garden space quite as well, adding a liner can help keep the dirt in place. This will save you money and work in the long-run by not needing to replace garden soil!

Adds stability

Added soil puts a lot of pressure on the sides of your raised bed. By adding a raised bed liner, this can add extra support and rigidity, increasing the lifespan of your raised bed. This is especially helpful if you are using thinner materials. 

Moderate temperature

A raised bed liner also helps moderate temperature fluctuations within your garden bed. Here in the upper midwest, our temperatures can vary widely, so this is definitely a plus! Plants are hardy and can handle a lot, but keeping the soil a consistent temperature certainly helps.

Common Raised Bed Liner Materials

There are several different materials out there that are commonly used as a raised bed liner. However, they all have their own shortfalls. Let’s break them down!

Plastic

Most gardening books recommend using plastic to line your raised beds, however, I’m not a big fan. It doesn’t breathe well, so the moisture will cling to your raised bed materials resulting in them breaking down faster. It’s a nightmare to work with and hard to get it to lay neatly.

Plastic also breaks down quickly and won’t last much longer than 2 years, requiring replacement. Lastly, who wants plastic surrounding their garden? I don’t.

Landscaping fabric

Using landscaping fabric seems like a simple solution, however the material is too thin to offer any benefits regarding stability or temperature moderation. Plus, landscaping fabric is a manufactured product that often contains chemicals and petroleum. 

Lastly, while landscaping fabric is meant to be a physical barrier for weeds, it’s still permeable and I would worry about pressure-treated wood chemicals leaching through it.

Cardboard

This is the least offensive option of the 3. It’s cheap, and would provide stability and temperature moderation. It’s a substantial enough barrier that it would likely prevent chemicals from leaking into your soil as well.

However, cardboard quickly decomposes and would need to be replaced year after year. I know I don’t have time for that!

What Should I Line My Raised Bed With?

Now we’ve come down to my secret weapon: cedar decking! While my favorite raised bed material is 2”x10” cedar boards because cedar is naturally rot resistant and doesn’t need a liner, these boards are VERY expensive. Just one 8 foot 2”x10” board is $86. Eek!

So, my new favorite option is utilizing cedar-tone, pressure-treated lumber and lining it with inexpensive, thin, cedar decking! This way, we are utilizing materials that have a long lifespan while keeping the toxins out of your food and without breaking the bank! What a deal!

How to Build a 4’x8’ Raised Bed with a Toxin-Free Liner

Here we go! Here’s everything you need to know to make your own raise bed with a toxin free, cedar lining!

Building materials

• Raised Bed: 3 x CedarTone Pressure Treated Lumber (2” x 10” x 8’) – $24 each
• Raised Bed Liner: 6 x Red Cedar Decking (5/4” x 5” x 8’) – $18 each
• Corner Stakes: 3 x Red Cedar Lumber (2” x 2” x 4’) – $8 each
• Screws for Raised Bed & Stakes: 1 box of 3″ Deck Screws – $7 per box
• Nails for Liner: 1 box of 2″ Galvanized Nails -$5 per box
• Compost and Top Soil: 26 cubic feet (or 1 full yard) in total

Tools

• Shovel
• Rake
• Tape Measure
• Power Drill
• Hammer
• Rubber Mallet (optional)
• Miter Saw (optional – can have lumber cut at building supply store and use a pull saw to cut the cedar decking to fit)

Step-by-step instructions

• Step#1: Lay out your materials before you start

• Step #2: Prep your materials by cutting 1 piece of CedarTone Pressure Treated Lumber in half so that you have two 4-foot long pieces. Then, cut all 3 of your 2”x2” red cedar lumber pieces in half (at a 45 degree angle) so that you have six 2-foot long pieces with a pointy end. If you don’t have a power saw, have your 2×10″ and 2×2″ boards cut at the building supply store. You can use a simple pull saw to cut the cedar decking boards to fit, later.

• Step #3: Mark the area for your raised bed. Using a shovel, remove the top layer of sod and place in a pile. Smooth the newly exposed dirt area with a rake.
• Step #4: Set your CedarTone Pressure Treated Lumber pieces into place and screw together using 5 screws per corner. You may need to pre-drill your holes to prevent the wood from cracking.

• Step #5: Assess your raised bed placement and adjust if necessary. Make sure it’s square!
• Step #6: Now we stake it down! Drive one of your angled 2”x2” Red Cedar pieces into each corner using a rubber mallet until the top flat edge is flush with the top edge of your raised bed. Make a mark in the middle of the 8’ long raised bed pieces and drive in 2 more stakes here to provide stability to these long edges. If you don’t have a rubber mallet, place a piece of scrap wood on top of the stake (to protect it), then use a standard hammer to drive it down.

• Step #7: Secure the stakes in place using 3″ deck screws screws for each piece, drilling from the outside in.

• Step #8: Time to add our cedar lining! Measure the length between each stake and cut your Red Cedar Decking materials accordingly. Since these pieces are only 5” wide, we will cut 2 pieces for each section and stack them vertically to cover the whole inner side of the treated lumber. TIP: Mark each cedar piece so you remember where they go after they’ve been cut!

• Step #9: Secure the cedar boards in place using 2″ galvanized nails.

• Step #10: Return the sod upside down to the bottom of your raised bed and break it up with your shovel.
• Step #11: Add a 1” layer of compost on top of the sod, then fill with quality topsoil and a bit more compost. Fill your raised bed until it’s 1-2” from the top of the frame.

Total Cost: $216

Yes, there are cheaper raised bed options out there, however, they lack durability and/or toxin-free materials. My design is the best option for combining long-lasting materials that won’t leach chemicals in your food. Plus, this design is also less expensive than other long-lasting, toxin-free materials like true cedar lumber, cinder blocks or bricks.

This raised bed design with a non-toxic cedar lining is built to last and will save you money and work down the road!

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Final Thoughts

Choosing what to use for raised bed materials is one of the most challenging things, in my opinion. There is no perfect material that’s inexpensive, durable and non-toxic. Often, you have to sacrifice at least 1 of those, until now!

Using my method of combining durable pressure-treated wood with a natural cedar raised bed liner, you have the best of both worlds! Plus, both materials are easily obtainable and fairly inexpensive compared to other options out there.