Can You Use Pressure Treated Lumber For Raised Garden Beds

One of the biggest questions you'll have to answer when you build a deck is whether to use pressure-treated wood or cedar. Which is better? Unfortunately, the question doesn't have a straightforward answer and both can be used with excellent results, if maintained, for years.

Cedar is known for its ability to naturally resist decay, nor will it warp when exposed to moisture. It's an excellent option if you want a natural look and feel for a deck. Pressure-treated lumber is cheaper than cedar and can last a similar duration if maintained properly. Overall, cedar will require less maintenance than pressure-treated lumber, although the up-front cost can be significantly more than cedar lumber.

For many, the choice often comes down to initial cost and the materials available at your local home reno store. Whichever choice you go with, understand that there are significant long term differences between the two types of lumber. Below we'll cover everything you need to know about pressure-treated vs. cedar lumber.

Pressure Treated Wood vs Cedar

Cedar Lumber: Quick Overview

Cedar stands out in any home reno store because of the color and grain pattern: straight, evenly spaced grain that is pleasing to the eye. To a lesser extent, the smell and color are also attractive. But not all cedar is from the same species.

Depending on where you are in North America, you may have a different type of cedar. In the Northeast and Eastern Canada, the cedar at your local home reno store is more than likely eastern white cedar. The rest of the country likely has western red cedar.

They both have decay and insect-resistant properties, but the colors differ and the girth and length of the two species vary so the availability of certain dimensions may vary depending on which type of cedar species is available in your area.

In general, western red cedar has a different hue than white cedar as it has a muted red tone, whereas white cedar is pale. White cedar is also a smaller tree. This makes it less desirable than western red cedar because the heartwood – the part of the cedar most resistant to decay and insects – is smaller. Thus you have a higher likelihood of getting sapwood, and not heartwood, lumber from white cedar than from western red cedar.

Both types of cedar, however, have the general characteristics that differentiate it from other types of lumber one would use to construct a deck or other project around the house. Below we'll take a look at the specific pros and cons cedar has versus pressure-treated wood.

Advantages of Cedar Wood

Cedar is nature's own pressure-treated wood, so let's take a look at some of the advantages of using it.

Decay and Rot Resistant – The acids and oils within the cedar tree are what give it the properties to resist decay, particularly when exposed to moisture.

Warp Resistant – Cedar is extremely low density with a very straight grain pattern making it resistant to warping in moist environments. The softness of the wood makes it malleable, which will help it resist cracking and splitting that typically speeds up the decay process.

Low Maintenance – Cedar needs only regular, minimal cleaning to keep its look and integrity. Over time cedar will weather into a silver-grey and you only need to clean it annually with soap and water.

Temperature Resistant – Cedar lumber can withstand cold and hot environments equally well since the low-density wood can expand and contract without splitting the wood.

Repels Insects – Just as the cedar resists decay and rot due to the acids – or 'phenols' – in the wood, it is also able to act as a deterrent to insects due to the same compounds in the wood.

Disadvantages of Cedar Wood

Cost – The main disadvantage of a cedar deck or other types of structure is the cost. Right now, cedar costs anywhere between 25 to 35 percent more than pressure-treated lumber.

Color – While the initial cedar color is very attractive, over time it fades to a silver-grey, which is not as attractive and may be a turn-off to some homeowners.

Soft – While the low density of the cedar has its benefits, it also makes for a relatively soft surface, prone to unsightly dents and dings that could bother some deck owners.

What is Pressure Treated Wood?

Pressure-treated wood is softwood lumber that is infused – treated – with preservatives to make it last in outdoor conditions.

The term "pressure" derives from how they treat the wood. Manufacturers take standard softwood lumber, bundle it together, then place it in a huge pressure tank. The tank is then filled with wood preservative and put under an ultra-high PSI. This forces the preservative into the wood.

Pressure-treated wood is either southern yellow pine (SYP), spruce, fir, pine (SPF), Douglas, or hemlock fir. The species of wood depends on your geographic location. Whichever species of lumber for framing lumber you can acquire will also be the species for the pressure-treated lumber.

Regardless of the type of tree used to create pressure-treated lumber, the more important factor is the type of preservative used in the process. Nowadays, the most common type of treatment used has copper in it and will carry the acronym CCA or ACA. They are both relatively safe to handle – with gloves and a mask – and resist moisture extremely well. When new, they also give off a greenish tint, which goes away relatively quickly.

There is a reason most people choose to use pressure-treated wood in outdoor applications. Let's take a look below.

Advantages of Pressure Treated Wood

Low Price – By far, the most attractive aspect of pressure-treated wood is the price. As mentioned above, it can often be found up to 35% cheaper – or more – than cedar.

Durability – Pressure-treated decks, properly taken care of, will last for over 10 years and up to 20 years or more. The key is regular maintenance.

Availability – Just about every home reno store in North America will carry pressure-treated wood. That includes deck boards and dimensional lumber, which also means you should be able to find a good price at any time of the year.

Insect Resistant – The chemical treatment of the wood ensures that bugs will want to keep out of it. The copper compounds are not ideal bug habitats.

Tough – Pressure-treated lumber is harder than other cedar lumber and will resist wear and tear better over time if maintained properly.

Disadvantages of Pressure Treated Wood

Hazardous – Treated lumber must be handled with care. If you are cutting it, you'll need gloves, a mask, and protective eyewear. You don't want to be inhaling the ammonia and copper compounds.

Corrosive – The preservative doesn't react well with flashing, and it will cause it to corrode. Specific green or brown coated deck screws are also necessary for treated decks, as the treatment will corrode typical galvanized or zinc-coated screws.

High Maintenance – Treated lumber on a deck requires regular maintenance – more than cedar. This costs you not only time but also money, as you'll need buckets of stain and the tools to apply it – numerous times over the lifetime of the deck.

Cedar vs Pressure Treated Wood: Key Differences

Let's break down the critical differences between the two types of lumber most commonly found in outdoor residential locations.

Appearance

Cedar has a straight, even, and narrow grain. It will have a pinkish-red color if it is heartwood or a pale yellow color if it is sapwood. Over time it will become silvery grey.
Pressure-treated lumber will be copper in color, with a wider grain. It will age to grey.

Decay and Rot Resistance

Cedar resists rot and decay because of the chemical makeup of the heartwood. Its low density allows it to flex in temperatures, resisting cracking, which ensures less moisture penetrates. This makes the cedar last longer in wet weather.
Pressure-treated wood lasts, but with regular maintenance. Since it is more prone to cracking and splitting, it will endure more moisture damage.

Color

Depending on the cedar species, you'll have anything from a russet color to pink to pale yellow. Over time, all cedar reduces to a silvery grey.
Pressure-treated wood is copper in color. This is purely a result of the preservative used to treat the wood. Over time this type of lumber turns a dull grey.

Smell

Cedar has the cedar smell that everyone is familiar with and it comes from the same chemicals – called 'phenols' – that make cedar rot and decay-resistant. Thus, lower quality cedar featuring mostly sapwood will not have the pungent cedar aroma.
Pressure-treated lumber does not have a specific smell, although the chemical treatment may give off an initial odor that wears away quickly once installed outdoors.

Hardness and Strength

Cedar is softer than the softwoods used for treated lumber. This is because it is less dense, giving it a flexibility treated lumber does not have. As such, cedar is very easy to cut and manipulate. The density does not take away from cedar's strength, however, although it is still slightly less than pine species and much less than fir and hemlock.
Pressure-treated lumber is denser than cedar, thus is less prone to dings and dents that cedar will experience at the surface. Pine is not strong as hemlock and fir species used in pressure-treated applications, but all are still stronger than cedar.

Durability

Cedar is extremely durable when it comes to weather. The expansion and contraction that comes with hot and cold temperatures do not necessarily affect cedar as it is not as dense as other softwoods, making it more malleable.
Pressure-treated wood is durable because of the treatment. However, once it splits and cracks, you'll need stains or paints to protect the wood further. Otherwise, water will penetrate the wood interior and you'll experience rot and decay. Even in treated wood.

Lifespan

Expect a cedar deck, with annual cleaning, to last at least 20 years without any rot or decay issues. After that, expect some of your boards to decay simply from water penetrating cracks from wear and tear.
A pressure-treated deck can last at least a decade – 10 years – before problems can set in. Weather extremes can affect treated wood, and ten years will see the cracks and splits in deck boards turn into decay and rot.

Cost

A 12' 5/4 cedar deck board at 6" wide will cost about $19, on average. An 8' 2×6 cedar board is about $14. The total cost for deck boards on a 10×10 deck would be $280.
For treated lumber, the same length of deck board will cost around $13. An 8' 2×6 of treated lumber is about $9. The cost difference is, therefore, around 30% cheaper for treated wood versus cedar. Treated deck boards for a 10×10 deck would cost $200.

Availability

Cedar deck boards of all dimensions are available throughout North America, although may not be as available in the Southeast, as there are no nearby geographic suppliers of that type of lumber.
Pressure-treated lumber is widely available in all locations in North America.

Installation

Installation of cedar is straightforward, without any special handling protection necessary. Cedar will accept standard deck fasteners of any type rated for exterior use.
Pressure-treated wood requires gloves, a mask, and eye protection when cutting. Cut ends should be treated to ensure ends don't rot. This lumber requires special, vinyl-coated screws as standard coated screws will corrode due to the chemicals in the preservative.

Maintenance

Cedar requires an annual cleaning, at a minimum. Applying a sealer is also recommended to ensure longevity. Other coatings, such as stains, are not required but can be applied to enhance durability.
Pressure-treated lumber requires an annual cleaning and a sealant or stain. Paint often does not work on treated wood as it will peel. Regular application and reapplication of semi-transparent or opaque stain are ideal.

Environmental Concerns

Cedar is an environmentally friendly product, as long as the lumber has been sourced from a sustainably managed forest, which the label will indicate.
Pressure-treated wood must be handled with care. When disposing of it, you must bring it to a special treated wood disposal site. You cannot burn treated wood.

Cedar and Pressure Treated Wood Best Uses

Besides simply building a deck, you can use cedar or pressure-treated wood in various outdoor applications. Let's take a look:

Fencing

A cedar fence is gorgeous, but unfortunately, when the cedar experiences ground contact, it can rot fairly quickly, even with its natural decay resistance. Using raised fence brackets to keep the cedar fence post off the ground is an option but may not achieve the look you want. Dimensional cedar lumber will almost always have sapwood, which is less decay and rot-resistant.

On the other hand, pressure-treated wood offers wood that is treated specifically for ground contact. Treated wood has different treatment levels. Wood with .25 preservative saturation is for above ground application, but you can buy treated wood rated for ground contact that contains .40 preservative per cubic foot. These are ideal for burying fence posts in the ground and will last 10 years in ideal conditions.

You can even buy treated wood with treatment levels of .60 at lumber yards, for extreme weather conditions, similar to railroad ties.

Outdoor Furniture

Building outdoor furniture with treated wood is not recommended for the simple reason that you shouldn't let exposed skin touch treated wood. The copper compounds on the wood can irritate skin and be harmful to inhale, so using the wood for furniture is not a good idea.

Cedar, on the other hand, is an excellent material for outdoor furniture, such as a minibar, table, or recessed planter. Since it is so light and easy to cut, creating furniture is a highly achievable project for any weekend warrior.

Pergolas

A pergola can use pressure treated or cedar lumber. The difference here is purely aesthetic. Since the structure is above ground, the same principles apply to the lumber for the pergola as they would for a deck.

Since a pergola won't endure the wear and tear that, say, a deck board would, then you might consider splurging on the more expensive cedar lumber simply because a pergola is more visible than a purely functional deck.

Saunas

Saunas should only be constructed out of cedar for several reasons. First, saunas are meant for extreme heat and moisture. Only cedar can withstand that type of environment without being damaged. Second, saunas are meant for people to sit inside and relax. People will be making skin to wood contact in a sauna, so you cannot use pressure-treated wood.

Even if you intended to use pressure-treated wood on just the floor and walls of a sauna, the heat combined with the treatment in the wood is not a good combination and should be avoided at all costs.

Cedar vs. Pressure Treated for Garden

Some people take pause when it comes to creating a pressure treated raised garden bed or box. However, modern treatments in the wood are highly unlikely to leach into the soil unless the wood is damaged and disintegrates. Therefore, treated wood is safe for gardens.

If you have a vegetable garden, it would be advisable to either have a barrier or move plants away from the edges to avoid having produce come in contact with the wood itself.

Cedar is a better option for garden beds and boxes, although once in contact with the ground, it may not last as long as pressure-treated wood.

Conclusion

When it comes to cedar vs. pressure-treated wood, think long term. While you may save several hundred or even several thousand dollars up front, you may lose out in the long term with increased maintenance costs and time spent taking care of a decking type you never wanted in the first place.

Remember that both cedar and pressure-treated wood can last a long time if properly maintained. Whichever type of wood you choose, be sure to take care of it regularly to ensure your investment.