Gardening with Kids: Building A Raised Garden Bed

I’m here with another article on gardening with kids. My gardening is mostly done in raised garden beds.  I’ve put together a total of 5, though the last two were to replace the first two I built. I like  the raised garden bed because it is a lot easier to work in since it requires less bending. That means you can reach into the middle of a bed without the risk of falling in. Plus, it keeps kids and dogs out without too much effort. They also look nice in the backyard, even in the spring and fall when nothing is growing. You almost look like you know what you’re doing.

Prepare the landing site

All of my raised garden beds are 4’x8′. I would convert that to metric, but I’m reading a lot of conflicting stuff on how lumber/timber is sold outside North America. In metric, it would be about 1.2m x 2.4m. Anyway, the 4′ is rather important, as most people can’t reach into the middle of a bed that’s much wider. If you have to go smaller or want to go larger, you make the raised garden bed shorter or longer. It could be a 4’x4′ square, or 12′ or longer. Multiples of 4′ are nice, since most lumber/timber is sold that way. Length doesn’t matter though, as long as you stay 4′ wide. That will help your kids as well.

To prep the site, I enlisted a few friends, rolled up the sod/turf (which was the easy part), then got to digging a hole that was slightly larger than the dimensions of the box. That was the hard part (and explained why the turf came up so easily). If your yard is less like concrete, you might not have as many problems. We dug down around 12″, exactly because the existing ground was so terrible. We dug up river rock (landscaping material), chucks of wood, and what I could only guess were the remains of prior buildings. But we did it.

If you have older kids, they can help with the digging if the dirt is soft enough. If not, they can always play gofer and grab water, tools, and other things. I have fond memories of working with my dad to dig out the pond he built in the backyard of my childhood home. I was 10 at that point, but you know your kids. Younger kids (like mine) probably will have to watch from the window, or be supervised by someone else.

Shopping list

Important note – Always buy untreated wood for a raised garden bed. Treated wood, like pressure treated or green treated, is preserved with copper and arsenic compounds. These are great for framing a shed in a damp location, but terrible for food. The heavy metals can leach into the soil and picked up by the plants. Instead, buy naturally rot-resistant woods such as cedar or white oak. They are more expensive than treated white pin or Douglas fir, but it’s worth it. If you are concerned about the sustainability of wood stocks, you can look around for stores that sell FSC-certified wood products.

Since I built 4’x8′ raised garden beds, I was able to take advantage of the fact the lumber/timber comes in lengths of multiples of 4. So I picked up 2 12′ boards and cut them down to 4′ and 8′ lengths. If you have a car that can’t handle 12′ boards (e.g most people without a minivan or sedan/estate car), 8′ boards will work. And if you have concerns about cutting the boards, most home improvement stores can cut to order.

In addition to the boards, I needed posts. These went into the corner of the raised garden bed to provide a little more rigidity and resistance to warping. Dirt is heavy, and even more so after a good soaking. The posts provide strength and something for the screws to bite into. For mine, I picked up 4×4 posts and cut them to 30″ (75cm). That used up a single 10′ piece with no leftovers. One thing I should point out is that my raised garden beds are 24″ (60cm) tall. If you are only going half that or less, the posts don’t have to be nearly as long. I think a good rule-of-thumb is to have about 6-10″ of post to come out the bottom.

To put it all together, I used deck screws, rated for the type of wood I was using. The screws themselves were 3″ (7.5cm) long to make sure they made it a good inch into the post. Each board was attached using 3 screws per side, for a total of 48 screws. If you are not using 2×12 boards like I did, you probably can get away with 2 per side.

Other than the supplies, I used regular tools like an , , (required if working alone), and a .

To summarize the shopping list for a single 4×8 raised garden bed that’s 24″ high

• 24′ of 2×12 cedar timber/lumber
• 10′ of 4×4 cedar post
• 1 lb of 3″ deck screws, designed for wood-to-wood fastening

You might notice some white posts attached to the sides in the photo above. Those are optional, and I explain more below.

Here’s a short video of my current raised garden bed setup:

Build that raised garden bed

For me, building the raised garden bed was the easy part. I put together the first raised garden bed entirely on my own. I estimate it took about 4 hours to build the raised garden bed by myself, and I’m by no means an experienced carpenter. Jenny was still in her first trimester with the boys and wasn’t having a lot of fun, but she did help fill the raised garden bed once it was in place. For the second raised garden bed, I enlisted the help of Rachel and her husband; that time it only took an hour or so.

Assemble the entire thing upside-down, with the posts sticking up towards the sky. I did this in my garage, but any flat, relatively level surface will do. I’ve never tried to assemble at the site, but I suppose it would be possible. It might just take a lot more work to make sure everything is level. A key note: If you are building it on your own, wood clamps are required. They will hold the wood to the posts and leave your hands free for leveling, drilling, and fastening the boards.

Rather than trying to describe in detail how I did it, I’ll just link to the instructions I used. Over at the magazine Sunset, there is a step-by-step guide to building a raised garden bed. It’s the general instructions I followed, with modifications. My modifications were with the second level of boards, longer posts, and no hardware cloth. I’ve never had a problem with burrowing animals, so it didn’t seem necessary. But if you have moles, voles, or other critters, there’s nothing wrong with using it. As for the rebar and PVC pipes, they are used to mount a floating row cover or bird netting.  On the first raised garden bed I added it, but it wasn’t used the first two years, so I skipped it for the second raised garden bed.

Once you get it completed, you just need get the raised garden bed to the site. I stupidly did this the first time by putting it on its side, put padding on my shoulder, then hoisted it up at the midpoint.  It was uncomfortable, took a long time, and not recommended. Assuming the shipping weights I found online are right, the entire raised garden bed weighs around 120 lbs, but it’s 8′ wide and 4′ tall.

Anyway, at the site flip it posts are down and level it out. This takes some time, and it doesn’t have to be perfectly level. In fact, I’m pretty sure my raised garden beds aren’t level anymore due to frost heave. But they are still close, and so should yours. Close to level makes it easier to level the soil, which means you won’t have low spots in the raised garden bed for water to pool in. Just make sure to pack in any leftover dirt under the posts to make it stable.

Fill ‘er up!

The last step is to get your soil of choice in there. This part takes the longest, since hand-wheeling and filling this box takes forever. I think, in my hazy memory, it was something like 30+ wheelbarrows full of dirt. The first time I did this, I was stupid and had the dirt delivered to the front yard. That meant a 100 yard round trip. Needless to say, it took me a couple evenings after work to get it done. The next time I was much smarter and had it delivered to the side yard. Make sure to fill it to the top, as once it gets wet, the soil mix will settle and you might find yourself with another 3-6″ of raised garden bed to fill.

For the soil itself, I used the internet to find a local provider. Most places around me require a 3 cubic yard minimum, which is find since it will take at least that to fill up the box. The place I went with had a mix that was made up of screened and pulverized black dirt, peat moss, and compost. If your provider doesn’t have a mix, you can try doing on that is about a third each of those materials. The black dirt is just dirt… it’s mostly filler. The peat moss helps with water retention and keeps the soil from getting to compact. And the compost is there to provide nutrients and minerals for the plants. All are necessary to start off with. As time goes on, you’ll likely top-dress with compost and other materials. I’ll cover that in a future post.

Just to address a possible controversy, let’s pause on peat moss. Peat moss is dead plant material that hasn’t really broken down. It forms over thousands of years, and it’s not really a renewable resource. Here in North America, much of it comes from Canadian peat bogs. Besides disturbing a natural area, peat bogs are huge carbon sinks. From burning fuel and natural or accidental fires, it’s estimated that about 5% of the total carbon output each year comes from peat moss. If I could find a local alternative that had the water retention and anti-compaction properties, I would go with that. Many can be found at hardware stores, like coconut fiber, rice hulls, and worm casings. And when I need to refresh the raised garden beds, that’s what I’ll use. But for the initial fill, you need a very thorough mix, and you won’t be able to do with a few bags from the hardware store.

After it’s filled up, I suggest a slow, long soak… for both you and the raised garden bed. The soil will settle out and compact a bit, which is why you want to go slow. If you go too fast, it will just sit on the top and not really trickle down. If I were to do it over, I might do the soak after every 6″ or so of dirt, just to make sure all the layers get wet. Peat moss doesn’t absorb water very quickly, especially when it’s dry. This is just another reason to slowly soak it, ideally for an hour, then do it again the next day. Obviously if you get a steady rain before planting, things will be fine. And if it settles too much, just add more of the fill.

Next steps

Now that the raised garden bed is built and filled, you can start thinking about plant selection. Our next article in the series will be about planning what you’ll grow, things to consider, and how to include your kids in the process.