If you are thinking of building some raised beds in your garden or allotment then you may well be wondering which wood to use. There are lots of different options out there at varying price points, but what works best for raised beds? What wood should you use for raised beds?
What wood to use for raised beds?
When building raised beds it is important to use treated wood or hardwood that will last for many years. Normal untreated wood will quickly rot down when used for a raised bed. This is because the soil will make the wood constantly damp and if you have ever worked with wood before you will know that damp wood rots.
Because of this, you must use pressure treated wood or hardwood. Hardwoods degrade at a much slower rate than softwood and even an untreated oak sleeper can last 30 or 40 years in the soil.
Pressure treated decking boards make great raised beds, in fact, I have a guide here on how to make a simple raised bed out of decking boards.
They aren’t the cheapest method, but they are also far from the most expensive and are probably the most popular way of building raised beds from wood.
Gravel boards are very similar to decking boards in that they are pressure treated boards made to be used outside. They work really well for raised beds and are actually what I used to build the raised beds in my new greenhouse.
Sleepers make for probably the most attractive and sturdy raised beds but come at a cost. While not prohibitively expensive in themselves, once you start adding up the cost of building a raised bed out of sleepers it can start to get expensive, especially if you plan on using hardwood sleepers.
In terms of sleepers, hardwood sleepers, usually made from oak, are the creme de la creme. They will last for decades with no treatment at all. Oak sleepers can last 30-40 years without needing any sort of preservative. But they come at a cost, and that cost is the impact on your wallet. Hardwood sleepers are not cheap.
The cheaper alternative to hardwood sleepers, but that doesn’t mean they are cheap. They will still be the second most expensive method of building a raised bed out of the options I have listed above.
What you will get though is a really substantial raised bed that will last for 10-20 years or longer if regular preservative treatments are applied.
What wood you don’t want to use for raised beds!
So you know what wood to use, but what woods should you avoid when building your raised beds? Well to start with, anything that isn’t treated shouldn’t be used if possible.
Untreated wood will be cheaper, but it won’t last long when used for building a raised bed. You could paint on treatment to the wood to make it last longer. But it won’t be as good as the commercial pressure treated wood where the preservative is forced into the heart of the wood at high pressures.
You also want to avoid reclaimed railway sleepers. While these things will last forever they are not suitable for growing plants in, particularly if you plan on growing fruit or veg in them.
That is because they were treated with some pretty nasty chemicals, which is why they lasted so long. These chemicals will leech into your soil and therefore into your plants. And if you are then eating what you grow in this soil it will inevitably end up in you. Stuff like arsenic was a regular treatment on old railway sleepers, so yeah, best avoided!