Pressure-treated lumber for raised beds can seem like a good idea, given its relatively low cost & durability. However, it’s NOT the best choice for where you grow food, since the preservative chemicals have safety concerns. So what are the alternatives?
There are many safer alternatives to pressure-treated lumber for raised beds, including: raw lumber (pine, douglas fir), composite timber, recycled plastics, logs, rock, brick, concrete blocks, steel, and stone. However, pressure-treated lumber is nowadays safer since arsenic-based wood treatments were outlawed in 2003.
In this article, we’ll cover:
- the problems of pressure-treated lumber,
- the various types of chemically treated wood,
- safer alternatives, and
- precautions to take if you have to keep working with pressure-treated lumber.
Is Pressure Treated Wood Safe For Raised Beds?
So, the quick answer is: For raised beds where you grow food, pressure treated wood is probably NOT safe.
First some background: Wood is a great building material since time immemorial. It’s lightweight, available, relatively inexpensive, and easy to work on with various tools.
However, wood is susceptible to rot and disintegration through decay when exposed to wet surfaces and/or is attacked by wood destroying organisms such as termites, beetles, bacteria, and fungi.
That’s a veritable army of attackers on your raised garden beds!
For those reasons, chemical treatments were developed to increase the durability & longevity of wood--not just for raised beds, but for virtually any outdoor use. So, whatever the outdoor project--fences, decks, playground structures, play forts, chicken coops, treehouses--you get the idea--treated wood came into use. Oh, and don’t forget telephone/power poles, railroad ties, seawalls, and various industrial uses.
Types of Pressure-Treated Lumber
So what exactly is pressure-treated wood?
Think of it this way: You can paint a chemical coating onto a piece of wood, but the chemical might only penetrate a fraction of a millimeter into the wood. That won’t give much protection.
So, to force the chemical to penetrate deeper into the wood, pressure treatment was developed. Basically, with pressure treatment, wood is immersed in a liquid preservative (basically a pesticide) and placed in a high-pressure chamber; the high-pressure forces the chemical into the wood fibers. The treated lumber is categorized by the type of chemical that has been used to treat it.
CCA -Chromated Copper Arsenate
CCA contains arsenic, which causes cancer in humans when ingested. Pressure-treated lumber sold before 2004 was treated this way and is therefore highly risky. The constituent chemicals would leach into the soil, and limited quantities would be taken up by the vegetables grown in these raised beds.
So, yeah, you can tell just from its name that it’s not something you’d want to use for raised garden beds--unless you want to ingest a carcinogenic cocktail of chromium, coppy, & arsenic.
ACQ – Alkaline (or Amine) Copper Quaternary
ACQ is currently the most widely used wood preservative for residential use, since it’s more ecologically-friendly than CCA. It has relatively low risks based on its constituents of copper oxide and quaternary ammonium compounds. This is less toxic, since copper replaces arsenic and is essentially non-toxic to humans, although research on the ACQ is still somewhat incomplete.
ACQ adheres to wood fibers well, allowing the wood to last for decades, even when in direct contact with the ground.
That’s great if you’re making telephone poles.But what if you’re growing garlic or tomatoes?
Well, the copper can still leach into the soil, and can be absorbed by your vegetables. Nevertheless, you can limit leaching by placing a plastic layer between the wood and the soil. Sigh...
The high levels of copper that have replaced the arsenic cause corrosion. Use stainless steel or galvanized steel connectors to avoid corrosion.
Creosote is a tar-based wood-treatment mostly used to treat railroad cross ties, utility poles, bridge timbers, and some marine structures. It’s very effective against fungi and insects. And, creosote can be sourced from plants.
Sounds pretty good, right? Not so fast.
Creosote is actually carcinogenic and, therefore, not suitable for gardening since harmful chemicals can leach into the soil and be absorbed by vegetables that you’ll subsequently consume. Sigh...
Note: As a rule of thumb, chemicals in treated wood aren’t healthy for people, animals, or the soil. If you use pressure-treated or chemically-treated wood for ANY project, use caution: wear gloves, avoid breathing sawdust by wearing a protective mask, and do NOT burn treated wood. Basically if you treat it like poison--which it kinda is--you minimize your risk.
Can You Use Pressure Treated Lumber For Raised Beds?
Um, did you read the section above? If not, I’ll give you the short answer: Pressure-treated lumber is likely NOT safe to use for raised beds--especially if you’re growing food in the raised bed.
Unless you want to roll the dice on getting cancer, avoid the chromium, copper, arsenic, & creosote cocktail that’ll leach into your soil from pressure treated wood.
Seriously, even if someone GAVE me a truckload of pressure treated lumber, I wouldn’t use it for raised beds.
What to Use Instead of Pressure-Treated Lumber for Raised Beds
OK, now that you’re sufficiently freaked out about pressure-treated wood for raised beds, what can you use instead?
Fortunately, there are a bunch of alternatives to pressure-treated lumber for raised beds:
Safer pressure-treated lumber
Well, though still pressure-treated, these use safer, ecologically-friendly chemicals that are essentially non-toxic to humans in place of the obnoxious arsenate, which is carcinogenic. For example: ACQ (for alkaline copper quaternary), wood treated with borates, and Copper borate azole (CA). I dunno about you, but I’d rather use my next favorite--raw lumber (which I KNOW is safe)--and repair/replace the raised beds more often.
It won’t last as long as pressure-treated lumber, but it’s certainly a safer option. Depending on the type of wood, it can be expensive--but unless you’re using high-grade hardwood, the cost for pine or douglas fir are reasonable.. Some natural woods like red cedar and redwood are rot-resistant, while wood from juniper, cedar, or ironwood naturally repel insects. Without the cancer-causing chemicals.
This is made up of mixing wood fiber, plastic (polypropylene), and some binding agents (i.e., glue). It can also be made from recycled materials and may have UV ray protection for added durability. This wood-plastic composite is stronger than pure wood. It needs minimal maintenance and is exceptionally durable. However, it’s got those chemicals--glues--that can leach into your soil, your veggies, and you.
A brilliant option that also manages waste is by recycling plastic. Additionally, it lasts long as the plastic is generally resistant to the elements.
What could be cheaper than assembling readily available logs to make up your raised bed? Since they’re basically raw untreated lumber, you shouldn’t expect them to last as long as composite lumber or the other durable medium. Nevertheless, they’re realistic alternatives that will get the job done and keep your raised bed together for a few years.
Brick beds are remarkably durable, giving you a permanent bed. They also give your raised garden bed a unique look.
They are inexpensive and particularly durable. You can build a raised bed super fast with cinder blocks if you decide not to use cement..
Concrete and Concrete Blocks
These make long-lasting raised beds that will most likely outlive you. Setting up concrete may require some skills and patience as they have a recommended drying time before use. But setting up will be fast and straightforward if you opt for interlocking concrete blocks.
Concrete Rubble (aka “urbanite”)
You can consider using urbanite for your garden bed, especially if they are readily available, from let’s say a demolished driveway or sidewalk. They may be unappealing but are quite cost-effective.
Raised beds made out of rocks are a beauty to behold and are essentially permanent. Setting up is what will take time as you have to use a mortar and consider the drying time. But they’ll be worth the wait given their permanence and aesthetic appeal.
Galvanized Corrugated Sheet Metal
These are budget-friendly, easy-to-set-up, and will last long as galvanizing protects the sheet metal against rust. They will also look good in your garden, even in an urban setting.
If you live in a climate with strong sun--at altitude or in the hot Southwest--using rock, concrete, brick, or sheet metal could make your soil too hot.
Precautions When Using Pressure-Treated Lumber
OK, but what if you’re ALREADY using pressure-treated lumber for your raised beds?
Should you demolish it, and replace the pressure-treated wood with a safer alternative?
Surprisingly, taking out the lumber is likely to expose you to more direct risks than keeping it in place. Disintegrating pieces and chemically-laden dust will expose you and your soil to potentially harmful chemicals.
Instead, you might just convert a raised vegetable bed to flowers--that way, you won’t be ingesting any of the chemicals, but can still have a productive raised bed.
So what are the precautions you’ll need to observe to stay safe when working with pressure-treated wood?
Pre-drill screw holes that are within an inch to the edge of the board. This minimizes the board's chances of splitting while fastening it, or later as the wood is drying up. Ensure you clean up all sawdust and dispose of well.
Collect as much sawdust as possible. You use a plastic tarp to collect the sawdust. This comes in handy, especially when working outdoors in the lawns, where it’s difficult to collect the sawdust by sweeping.
Use a dust mask and eye protection when working with pressure-treated wood as it irritates the eyes, nose, and skin.
Use appropriate rust-resistant fasteners. The newer pressure-treated woods (such as ACQ) that are copper-based are corrosive to the fastening materials such as screws or nails. It’s advised you use galvanized fasteners or a kind that’s resistant to rust.
Purchase an appropriate grade of pressure-treated lumber. Buy ground-contact grade pressure-treated lumber for raised garden beds to ensure it lasts long.
Do NOT burn pressure-treated lumber. Burning treated wood can release chemicals that are dangerous to your health. Inhaling the smoke is a health threat as some pesticides used in the woods are known to be carcinogenic. The ash produced is even more toxic.
Newer, more ecologically friendly pressure-treated woods have replaced the arsenic-based treated lumber since it was outlawed for residential use in 2003.
Besides, there are numerous practical alternatives to pressure-treated timber, some being just as durable as pressure-treated timber.
For my money, my family’s safety, and my peace of mind, I’d recommend that you use natural materials only for raised beds: raw lumber or stone.