When you are building a raised garden bed, material is often the first consideration. The easiest thing to do, by far, is to use whatever you have on hand. Almost every homeowner has a scrap wood pile laying around. So, would it be safe to use plywood for your raised beds? Well, that depends. Let’s take a deeper look.
1. What is Plywood?
The first thing we have to consider is what, exactly plywood is. Did you know that not all plywood is created equal? There are actually varying grades of plywood and, as it turns out, this can make all the difference in the world.
Knowing what type of plywood you have will tell you a lot about whether you should use it in your garden. Let’s take a look at some of the common types of plywood.
Plywood is comprised of thin layers of wood, called veneers, sandwiched together to form a rigid board. More layers give you a thicker piece of plywood.
Aside from that, there are various types of wood that can be used in plywood as well as different “grades” of lumber.
For our purposes of using raised beds, there are two things we need to consider, the type of wood and the bonding method.
Let’s have a look at the two most important factors to consider when deciding whether to use plywood for your raised garden bed. First, we’ll start with the wood type.
2. Plywood Type
|Plywood Type||Common Wood Types||Suitable for Raised Garden Beds|
|Softwood||Pine, Cedar, Redwood||Yes|
|Hardwood||Birch, Oak, Walnut, Maple||Yes|
|Fiberboard (MDF)||Hardwood Outer Layer, Fiberboard Internal Layer||No|
|Particle Board||Wood slivers glued together.||No|
The biggest thing to consider with choosing the type of plywood is that your garden beds are going to be exposed not only to the elements, but hopefully also to healthy, moist soil.
Now, granted, you could use a liner. That will certainly protect the inside of the wood from moisture but, unless your raised beds are fully covered, the outside of the wood will have rain and sun exposure as well.
You want to make sure your plywood can withstand being outside in the elements. Now, if your scrap wood pile IS outside, and your plywood looks OK and sturdy even having been left out, then it is probably a fine enough quality wood to use for your raised beds.
3. Plywood Construction
As I mentioned, plywood is merely thin layers of wood sandwiched together. But, how do they “stay” that way? The answer to that is simple, glue.
This video from the Home Depot is an excellent 2 minute clip and super educational!
Glue is where another concern can come into play. If you know the wood you have on hand is PureBond plywood, you don’t have to worry about there being any harmful chemicals in the glue.
PureBond plywood is made using a soy based, formaldehyde free glue. But, not all plywood companies are the same. It is very important to research the type of plywood you are using.
Learning what types of glues were used in the manufacturing process is important for peace of mind that you can safely eat the vegetables growing in your raised garden beds.
Wood is natural, soil is natural and the whole process of gardening is pretty natural. The thing you have to take into consideration in any situation is decomposition.
Anytime you expose untreated wood to moisture, decomposition starts taking effect. Eventually, over time, a bed made out of wood will start to decompose and degrade.
Depending on the type of wood used, you could get 3 years out of your bed or 30. With plywood, you are likely to see decomposition happen much faster than using solid wood.
Instead of one hard, solid piece of wood, you are using thin layers sandwiched together. Over time, the glue will weaken the bond between those layers and they will individually start to decompose rather than the one piece of wood as a hole.
Most of us have seen this happen to old plywood boards left out. They tend to curl up at the edges and start to separate.
Again, this is a process that can take years, depending on the conditions, so it isn’t something you need necessarily worry about now but you should consider it when choosing materials.
5. Using a Liner
If you aren’t sure what type of adhesive was used in your plywood, or how it was manufactured, you should just use a liner.
There are many types available but, most commonly, a heavy plastic liner should provide a good barrier between the plywood and the garden soil. (source)
Be sure, though, that you don’t punch any holes in the liner when tending to your garden. This would allow soil and water out, but also any harmful chemicals in.
6. Economical Alternatives
The other thing you have to consider is, are there economical alternatives. Using scrap lumber, that you have on hand is about as cheap as it gets. I mean, you can’t beat free right.
If this bed is just for flowers, you are probably good to just build it and let it be. It’s using the bed to grow food when you want to be much more cautious.
Consider using any of a wide variety of economical alternatives. If your scrap pile includes any of the following, they would be excellent alternatives to plywood:
- Leftover cedar fence pickets
- Galvanized metal roofing
- Leftover sheet metal
- Leftover landscaping rocks / blocks.
The final thing to consider is how long you want or need this bed to last realistically. If you are just using the bed for a couple of seasons, throw together what you have, pop a liner in and move on with your day.
If you plan on these beds sticking around for a long time, be a bit more judicious about what materials you use. If you do go with plywood, choose a hardwood and a glue that is generally considered safe.
Remember, even if you do use a liner, you don’t want to worry about “did the liner puncture”, “does this zucchini taste funny”, etc.