Raised gardens can be bought as a kit or constructed completely as a DIY project. Regardless of how you get your raised garden, they can be a wonderful way to grow veggies. However, they do have one downside. If made of wood, they will eventually rot. Decomposition is inevitable. But, there are ways to construct a raised bed that will lengthen the life and the looks. Because I wanted to do both, I decided to construct a DIY composite raised garden.
One thing that I was concerned with, before choosing my materials, was safety. I wanted something that would last and look good for a long time, low maintenance, etc. But, I did not want to sacrifice safety.
I immediately decided against pressure treated lumber. I know that the newer stuff is supposed to not contain high levels of arsenic, as the pre – 2000 lumber did, but I do not feel confident in using any wood that has been drenched in chemicals. I know that there are many who use it and just line it with a protective membrane. However, I still feel concern for the leaching that will occur in the surrounding soil. I am mostly concerned with the fact that the roots of my plants will eventually penetrate any membrane and mingle with the surrounding soil.
So, that leaves me with a rot resistant wood (such as cedar) or a composite material. Since, I wanted something that will look nice, I checked on the composite wood. I discovered that it is made from a combination of wood fibers and recycled plastics. (This is the important part).The plastics that are used in the majority of composite wood is high density polyethylene. (HDPE) HDPE is the same plastic from which milk jugs are made. It is suppose to be safe for raised beds and is not suppose to leach chemicals into the soil. So, I decided to give it a go. (I am including a link below to a site that lists the different brands of composite wood and their properties).
Now, I know that everyone will have their own opinions on which material is better, safer, more efficient, more economical, etc. And I concede that composite may not be the best for every situation. This is just my preference. You have to decide for yourself which material is best for you. But regardless of what you choose, this layout can work for any material.
This is the raised bed that I built 3 years ago. Glad that I had the foresight to take, at least, a few photos.
DIY COmposite Raised Garden – Materials
The materials that I used are :
- (11) 1″ x 6″ x 8′ composite boards. ( If not adding a top, only 7 boards are needed).
- (6) 4″ x 4″ cedar posts cut to 12″ lengths.
- Composite screws
- Galvanized steel wire mesh fencing with 1″ x 1″ openings (optional)
Steps for DIY Composite Raised Garden
1.Prep the location for the raised bed. I measured my spot for a 4′ x 8′ section, plus additional space to add a brick border.
- Next, remove all sod from the area. I found it easiest to score the lawn in 12″ strips. This gave me a perfect area to push and roll up the sod with my shovel.
Now onto the assembly. Cut (3) of the composite boards in half. (Be precise – especially if using mitered cuts). You should end up with sections that are just 1/8″ under 4 feet.
- Attach the bottom boards (3 cut board sections and 2 uncut boards) to the cedar posts, making sure that the short end boards are placed to the inside of the longer 8′ boards.
If using the wire mesh (use this if you think that you might have an issue with voles or moles), this is a good time to attach it. What I did was flip the bed over and staple the mesh to the bottom of the bed using my pneumatic staple gun. However you choose to attach the mesh, just make sure that the attachments are spaced no more than every 2″. Otherwise, a mole/vole may be able to work its way through.
4. Next, attach the second level of boards. (Note: although the sketch doesn’t show screws on the middle (dividing) boards, I attached these to the cedar posts from the inside. Then attached the 8′ boards to the center cedar posts from the outside. These center boards serve two purposes. (1) They provide support to the composite boards and will keep them from bowing out from the weight of the soil. (2) They provide a separation so that I basically have 2 side-by-side beds).
- Next, if adding a top, carefully miter the corners. The 8′ boards will need to have the miter cut so that it falls right at the corner. If you do not want to miter the ends , you can always just butt them to each other. But if mitering, measure twice. Then, measure twice more before cutting.
Then, add a layer of cardboard. I placed a layer of newspaper under the bed and cardboard on top of the mesh. In the image above you can see the mesh showing on the far side, with the newspaper beneath. This does 2 things. (1) It serves as a temporary weed barrier, just in case there are any sod roots left behind. (2) It provides food for the worms.
As you can see in the image above, I am putting a border around the bed with some leftover house bricks. In case you are wondering about the landscaping fabric, I am just using it for the brick edge. (Still need to tamp the bricks down level).
I occasionally get questions about what I used to fill the bed. I don’t have an image of my mix, but I do something similar to the above image. In a wheel barrel, I mix equal parts of the following:
- peat moss
- worm castings
- mushroom compost
- manure compost
- cotton compost
I used a 5 gallon bucket to measure equal amounts of each into my barrel. Then, I mixed the batch and dumped it into the bed. Repeat, repeat, repeat, until the bed is full. I don’t recall the exact number of bags that I initially needed. I believe it was somewhere around 4 of each compost/casting. One large cube of peat moss and a huge bad of vermiculite. (I mean huge!)
Each year since, I have added 2 bags of worm castings (1 to each side) and a little bit of a fertilizer called “Chickety Doo Doo.”
I plan to add a bit of the other items as I feel they are needed. The peat moss will likely be added every 4-5 years.
Total cost for this DIY composite raised garden was around $200. I know that the initial cost for my DIY composite raised bed was more expensive that a lot of other DIY beds. But, I feel confident that I will not need to do any maintenance for many years. When it does require maintenance, it should only be to replace the cedar posts. But right now, it is still looking good and holding strong.
These are a few images of my first year veggies.
First baby salads of the year. I use one side of the bed to grow baby salad throughout the spring.
First year red potatoes. I did not leave these to grow until the late fall, because I had an issue with flea beetles. I pulled these up in September. But, I was happy with the outcome. I just planted a small bag of eyes.
First year summer haul. This was my first haul for the summer. I had a 1 Roma tomato plant, 1 bush tomato plant, 1 baby bell pepper, 1 baby (can’t remember but they were yellow) pepper, 1 jalapeño pepper and a bush variety of cantaloupe. I also had a few carrots and green onions, but they didn’t make it in this haul. :-)
As promised, here is the link to check the content of the different composite brands. What you are looking for is a combination of wood and HDPE. http://www.deckspecialists.com/composite_deckmaterials.htm