The top question asked on Suburban Hobby Farmer is what’s the best material for raised garden beds?
That’s because, for a concerned organic gardener, picking the best material to build a raised bed is a challenge. This is especially true if you are concerned about leaching of chemicals into the food you eat.
When it comes to the best materials for raised garden beds, backyard gardeners want:
- It to be attractive because who likes an ugly garden.
- It to last because building can be costly and time consuming.
- It to keep the varmints out so you’ll have vegetables when all is said and done.
- It to be easy because who has time to be both a gardener and a carpenter?
They want some other things, too:
- It should drain well.
- It should warm the soil more quickly.
- It should raise the dirt up, so that it’s easier on your knees
Some types of raised garden beds allow you to add fencing or covers to keep pests out or to trap warmth and extend the growing season.
Related: Mulching Raised Garden Beds
But the main reason for a raised garden bed is to keep the dirt inside separate from the rest.
So, with these ideas in mind, I looked at the different options for materials for raised garden beds, including:
- Pressure Treated Wood
- Composite Wood
- Cement Blocks or Bricks
- Fabric or cloth
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People are astonished when I tell them that fabric is the best material for raised garden beds. They ask me what are you talking about?
Cloth or fabric raised beds are essentially big pots made out synthetic, flexible materials. The makers of fabric raised beds stitch together the materials to make big bags that you fill with soil.
These big bags hold soil like any other raised bed and come in a wide variety of shapes and sizes. Although they take some getting used to, people love them!
Why people love fabric raised beds
They love them because they are:
- Easy and fast. Just unfold and fill with soil. There’s nothing to build.
- Not expensive. They cost less than the materials for other types of raised beds.
- Easy to make level. This is important for watering and planting.
- Not bottomless. The bottom layer of fabric seems to prevent voles and mice from tunneling into your soil.
- They drain well, but are still pots. The soil you use should be light, just like the soil for a pot.
- Good conductors of air, which is great for roots and beneficial creepy crawlies and microbes.
- Less likely to leach chemicals, which is much better than other materials. Many are BPA free.
Voles and mice could probably chew their way into a fabric pot. But they seem to avoid it. Maybe this is because they don’t like the smell (I can’t smell anything).
I mix my own soil for raised beds. I use garden soil, compost or manure, a little peat moss and perlite. You can go a little heavier on the garden soil than for regular pots, if you want, because fabric raised beds conduct air and drain well.
The downside of fabric raised beds
No question, fabric raised beds bulge more than ridged materials. People have trouble getting used to this.
But you can change this by strategically placing rocks or other weighted materials in strategic locations next to the bed.
Other characteristics that people don’t like:
- They have a bottom. Some people want worms & other beneficial creatures to come and go from the raised bed.
- The soil at the edges dries out, and it is difficult to get water to the edges.
- Fabric raised beds have a limited life. Usually they last about 4 years. Your results may vary. Emptying and storing them before cold weather extends their life.
- You can’t attach fencing or season extending covers to them.
- Shoveling dirt out can be difficult. It’s easy to damage the bed with a shovel.
If you pierce the bed on bottom with a shovel, you could probably still use it. But a rip on the side would end the life of the bed.
Untreated wood is the most common raised bed material. It’s common because it’s relatively easy and inexpensive.
Typically, you use some kind of joining device, e.g., brackets and screws, to make the rectangle.
Wood raised garden beds have many advantages.
There are many types of wood you could use to make beds. The general rule is the softer the wood, the shorter the life span of the material.
Something like pine typically will only last four years. Cedar, on the other hand, may last as much as twenty years or more. Unfortunately, wood that lasts tends to be very expensive. Alternatively, softer woods cost much less.
Raised bed kits are typically made from wood. The really nice ones are cedar. They last a long time and look great but cost a lot. Still, a cedar raised bed is probably a good investment because of the long life span. You may never need to buy anything else.
Why people like untreated wood raised garden beds
Wood is a very popular raised bed material. With good reason. People like it because:
- It’s inexpensive and easy
- You can make it as high or low as you want. People who have trouble kneeling can make them very high.
- You can attach a fence or season extending cover.
- It’s completely non-toxic. In fact, worms will feed on the wood and love it.
Why people don’t like wood
The biggest downside to wood is its short life. To extend the life of wood, you can use an organic wood preservative, e.g., Eco Wood Treatment.
If you want wood, Eco Wood Treatment is a good solution.
Other problems with wood include:
- You must have some simple carpentry skills.
- It’s inflexible, making it difficult to create round beds.
- You need a joiner of some type.
- It will attract termites. Wood, half buried in the ground and watered frequently, is their favorite food.
Pressure treated wood
All I’m going to say about pressure treated wood is don’t use it to grow food. In fact, don’t use it if at all possible.
Even the newer versions like alkaline copper quat (ACQ), which is better than chromium copper arsenate CCA), are bad for your health.
A fun fact about pressure treated wood is that it is called “pressure treated” because the wood is placed in a depressurized holding tank that removes air and replaces it with poison.
Composite lumber is made from a combination of wood fiber and plastic. It’s held together with a binding agent to make the boards.
You probably know that a lot of decks are made from composite lumber because it doesn’t break down as quickly as untreated wood, but isn’t as toxic as pressure treated wood.
Why people like composite lumber
Sounds like a pretty good solution … right? A lot of people like composite because:
- It lasts, even when directly in the soil.
- It’s more flexible than untreated wood. So you can bend it a little.
- It has a very “finished” look because it looks like stained wood.
- You can easily attach fencing or a season extending cover.
Why it’s disliked
There are, however, reasons why composite wood is not the top choice:
- Termites will eat it, although it’s less likely than untreated wood.
- Between the adhesive and the plastic, there’s a good chance there is some toxic chemical leaching.
- It’s expensive, but not as much as cedar.
Plastic raised garden beds
Plastic is both durable and some people think it’s attractive. Plus, it’s inexpensive.
So it’s got some good things going for it.
But even the good plastics, e.g., HDPE plastics, have leaching issues. Scientists have shown that chemical contamination of soil does occur.
Your best bet is to use food safe plastics when growing food. But good luck finding a raised bed kit that is made of food safe plastic.
It probably would break down very quickly in the sun anyway.
Cement blocks or bricks
Cement building materials and bricks last for a long time. Plus, they make it easy to create raised beds.
Since they are discrete units, you can gradually bend a wall and create uniquely shaped raised beds.
They also have the advantage of not being very expensive. In fact, because of their long life, you will often have access to them for free.
But the problem with cement and other building materials is that you don’t know where the raw materials were sourced and what went into them. More than likely, the materials in cement blocks are the cheapest possible.
At best, cement will increase the pH of the soil as it breaks down. At worst, it will contaminate the soil because the materials used to make the blocks were hazardous.
One more point about cement blocks or bricks: It’s nearly impossible to SECURELY attach fencing or season extending covers to it.
Stone raised beds
For many, stones are the least expensive raised bed building material. You may already have them on your property.
But their irregular shape makes them inconvenient. This is because irregular shapes mean it will be time consuming to create a stone raised bed of any height because you must put the stones together like a puzzle.
Steel or metal raised beds
Metal raised garden beds have the advantage of lasting for about 10 years. This is a real advantage over other materials.
They also are attractive and easy to assemble.
The two main problems have to do with:
- Leaching of chemicals and metals into the soil
- They are sometimes expensive.
All metal raised beds will contribute metal to the soil overtime, so I would avoid growing food in them.
Fabric raised beds have some really strong advantages over the alternatives for creating raised beds. They are pretty inexpensive, fast to set up and you can put them nearly everywhere.
If you know of a better alternative for constructing raised beds, let us know by commenting in the comment field below.
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