Planning some garden construction projects for next year? Are you wondering which is the best lumber to use, that will last a long time and look great?
There are many structures in the garden that use lumber of one type or another. Raised vegetable beds, compost bins, fences, pergolas, arbours, greenhouses, planters, decks and even chairs and tables.
Wood has usually been a go-to material for these types of structures as it is readily available, easy to work with the right tools and feels warm and inviting to the touch.
Since these structures are outside, exposed to the weather, they need to stand up to adverse elements and last. Otherwise, you will end up having to replace them on a regular basis and that gets to be very expensive!
So what is the best lumber to use to avoid having it rot into the ground? And since your goal is to create a tranquil garden, that is pleasing to your eyes, what lumber is visually appealing without much effort?
Note: Not a Do-It-Yourselfer (DIY)? This information is still valuable if you are hiring someone to build the structures for you. It is always a good idea to be informed, so that you know when someone is telling the truth versus trying to cut corners.
Non-treated Pine, Spruce, Fir, etc.
These softwoods are usually the cheapest lumber you can buy at least in temperate regions where these evergreen trees grow. This is the main reason why it is the most common lumber that novice gardeners use, especially when on a tight budget.
Generally, these are not recommended for use in the garden if left exposed to sun, rain wind and cold temperatures. Especially if they are touching the ground. I originally had made my raised vegetable beds with untreated fir boards. They lasted only a few years before rotting into the ground.
If you do decide to use these softwoods, you need to protect them with a stain, paint or another preservative. And do not use them for ground contact. Always try to elevate them on bricks or stone to keep them from being in direct contact with standing water and wet dirt.
Aesthetically these can look nice if stained or painted. Keep in mind though that paint will flake off if exposed to direct sunlight and battered by rain and wind. Stain is a bit more durable as it sinks partially into the wood, but eventually, it too will wear off. So it will require regular maintenance at least every few years.
Pressure Treated (PT)
This lumber generally is pine, spruce or fir that has had a preservative forced into the pores of the wood under extreme pressure. This lumber comes in various appearance grades, ratings for ground exposure and different preservatives. This page has a good overview of the different kinds (US-centric though).
For fence posts or other permanent structures where you need to have lumber buried in the ground, PT lumber makes sense. There are other techniques to use to ensure that even the PT lumber doesn’t start rotting pre-maturely but that is for another article.
However, for ground contact around food you are growing such as for raised beds, planters and even compost bins, I would not recommend PT lumber. PT lumber used to be treated with CCA (chromated copper arsenate), which was discontinued because of health risks of long-term exposure to arsenic. PT lumber now is preserved with either CBA (copper boron azole) and ACQ (alkaline copper quaternary).
There is a lot of debate whether or not these new preservatives are safer around food crops. I am not going to take any chance with my family’s health, so I have decided not to use it. If you do decide to use it for raised beds or planters, at least consider lining the inside with plastic sheeting. It’s a good idea regardless of what wood you use, as it will also keep the wood from rotting where it is in constant contact with wet soil.
Cedar and Redwood
Usually, when you see photos of beautiful decks and other structures in magazines and online, these are built from either cedar or redwood. These two softwoods are very rot-resistant, insect-resistant and durable.
Both kinds of wood have been and are still used by indigenous people in North America to build their houses, canoes and totem poles. While they will rot away eventually, they fare better than the other softwoods mentioned above.
I use cedar exclusively in my garden. It is readily available on the west coast of Canada, so the price is relatively inexpensive compared to some of the hardwood lumber mentioned below. It machines well, smells great and comes in many different sizes. So I consider it the best lumber to use for garden projects.
Cedar and redwood both weather if unprotected to a silvery gray colour. I personally do not like seeing this as I believe if you are spending the money for these beautiful woods, they should be protected to keep their natural reddish brown colour. I use a low VOC (volatile organic compounds) sealer that has UV (ultra-violet) protection.
If you have cedar or redwood that has aged, you can bring it back close to its original colour with some simple cleaning techniques, which I’ll share in a future Quick Tips post.
You will see exotic hardwoods used for high-end decking projects, mainly because of their resilence to moisture and their unique grain patterns and colours. The most common ones used are ipe, cumaru, tigerwood, teak and garapa. Cost can vary, but they all are much more expensive than the above softwoods. And they can be hard to source – you likely won’t find them at your local home centre or lumberyard.
The other two issues with using these exotics are workability and environmental impact. Hardwoods, in general, require very sharp and powerful saws to cut, which the average homeowner might not have. Some are also very abrasive to cutting tools, so you may find you need to sharpen or replace cutting edges more frequently if you cut a lot of exotic hardwoods.
The environmental impact is also a consideration. In the past, some of these hardwoods were cut to clear land for cattle and contributed to the decimation of the rainforests. Now you can find hardwoods that are more sustainably harvested, but it requires a bit of research to find the right suppliers and sustainably harvested hardwoods will likely be even more expensive.
If you live in the Americas, Europe or Asia, oak is usually readily available. It is more expensive that softwoods but less expensive than the exotic hardwoods. For outdoor use it is very durable and insect-resistant. Wagonwrights used oak for building wagons that withstood hard conditions.
Typically you can find both red and white oak. It is a very heavy, dense wood so, as with the exotic hardwoods, it will require very sharp cutting tools.
This is a relative newcomer on the market and can be worked with regular woodworking tools. It is mainly used for deck boards as one downside is that it has less structural integrity than real lumber. So it needs to be adequately supported and can’t be used for structural purposes such as deck framing.
There are various different manufacturers and just as many manufacturing techniques. Best to check what is locally available as this can vary and affect the price.
Composite lumber is more expensive but it is marketed as being more durable and rot-resistant. Plus some composites are made from recycled materials such as sawdust and plastic bottles. It does require maintenance, usually some form of cleaning that doesn’t damage it. Some lower quality composites are affected by sunlight and will fade over time, so make sure the lumber has UV blockers all the way through the material.
As you can see there are lots of choices for lumber. Picking the right lumber for the right application is crucial for a successful construction project. Future articles will expand on this post and provide information on how to construct with lumber in order to minimize the common places where rot occurs first. And how to maintain and restore your wood structures to maximize their life and appearance.
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Do you have a preferred lumber species you like to use? Do you have any upcoming construction projects that you need advice on? Please leave a comment to start the discussion or you can catch me on social media.