How To Build Elevated Cinder Block Garden Beds

Do you have lousy soil but want to start a garden? Got cinder blocks? Build a concrete block raised bed garden!

The advantages to raised bed gardening are many:

They're easier to weed (less bending over).
There's no tilling required (less compaction from stepping on the soil).
They're easier to work (again, less bending over).
You can build your own soil.
The soil warms earlier in the spring.

The disadvantages to raised bed gardens, particularly concrete block raised bed gardens, are that they require extra labor and cost to construct. They also tend to require more watering. People build their raised bed gardens in a variety of ways. If money is no object, you can use red cedar or stone. Some use pressure treated lumber while others refuse on toxicity grounds. It's largely a personal choice. The lowest-cost option to build raised beds is actually free, you just pile the dirt into mounds. I prefer concrete blocks!

Why concrete block raised bed gardening?

Concrete blocks are easy to salvage from random places: vacant lots, behind barns, and wherever else.
They provide a nice, wide platform that you can sit on to plant, weed and water.
No drilling or screwing required, just drop into place.
Easily adaptable to form hoop houses, screen plants, etc.
I think they look kinda cool.

I began construction of the first bed in the late summer so it'd be ready for spring planting. That also gave weeds a chance to grow, which I then killed, reducing the next year's total weed count.

This is how it looked at the first phase:

What may not be apparent in the photo is that I actually dug out dirt for the first row of concrete blocks so they'd sit below ground. I thought this would help stabilize the bed a bit from frost. The bed is loose fit (no mortar), and I didn't want to find the bed heaved all over the place with the spring thaw. I'm not sure if it was necessary or not, but the bed still had nice, level lines after winter. You could save some work (and materials) if you made the bed one row shorter.

In the background of the above picture you'll see four piles of dirt. The one on the far left is aged horse manure. In the center at the far back is screened loam. The smaller, darker pile to the right of that is homemade compost. And the pile in at the right, with the shovel sticking out of it, is the crap, clay-like soil I dug out of the ground.

I mixed the aged horse manure, screened loam, and compost together in the wheelbarrow (1/3 of each). Check the action:

Note that it appears two blocks high here (one row buried).

You can see I had to fence the raised bed because of the deer. You can also see that I capped the walls with additional flat blocks. I already had some on hand and it gave a nice, finished look that doubled as convenient seating for weeding.

Optional Construction Ideas

Concrete blocks may wick some of your water. You can line the inside walls with plastic sheeting if you want to prevent this; and in retrospect, I should have done this. The plastic can be tucked under the upper flat to hold it in place. Cut the plastic off at the base of the walls before back-filling the bed with soil. Never run plastic under the bottom of the bed. You need the drainage.
For super duper stability, you can drive rebar inside the block holes and back fill it with gravel. That was my original intent, but then the "overkill" voice was ringing in my head. I didn't deem it necessary. Besides, if blocks do move, they're easily re-aligned. Because the soil doesn't compact, it's simple to shovel dirt away from the wall and re-set any blocks. The soil stays nice 'n fluffy.

Here are additional pictures:

Raised Beds are Ideal for Square Foot Gardening

Pictured here is some eggplant, peppers, and broccoli. Already harvested from the raised bed was radishes, carrots, two types of lettuce, and spinach.

I coupled the raised bed with the square foot gardening technique. If you're new to gardening, it's a great way to get a grip on planting and spacing. It's a technique that's similar to the long-used French intensive gardening approach. From Wiki:

French intensive gardening, also known as biodynamic, raised bed, wide bed, or French market gardening, is a method of gardening in which plants are grown within a smaller space and with higher yields than other traditional gardening methods. The main principles for success are often listed as soil improvement, raised beds, close spacing, companion planting, succession planting and crop rotation. Originating in France, the practice is popular among urban gardeners and small for profit farming operations.

If you're new to gardening, and in particular, square foot gardening, you'll want a copy of Mel Bartholomew's best-selling book All New Square Foot Gardening.

Building a Plastic Tunnel Cold Frame

You can extend your growing season on the early and the late end by building a plastic tunnel over your bed to protect your plants from colder temps. While I didn't do it over my concrete block raised bed, it is easily accomplished. You can essentially build this setup right on top of it.

Instead of screwing the flexible Pex tubing into boards, you can insert that tubing directly into the holes of the cinder blocks (without the flat concrete cap stones on top, of course). Run some rigid PVC tubing (available at your local home improvement store) lengthwise across the flexible tubing just like in the picture. Cinch the PVC to the Pex tubing with zip ties. Run vinyl gauge fence over the frame (just like in the picture) and cinch it with the same zip ties. You can buy the garden fencing here or at your local garden store.

Then cover it all with plastic, something like DeWitt Supreme Plant Frost Protection Blanket. When the cold period has passed, keep your frame in place and then use insect netting over the frame to protect the plants from destructive bugs.

Related Raised Bed Garden Supplies

A roll of twine is great for square foot gardening.

Inside the bed in the picture above you'll see strips of scrap lumber I zipped off to measure square foot grids. What also works to mark your measurements is a simple roll of inexpensive, biodegradable twine. Using a concrete block bed like the one in this post, you can hold the lengths of twine in place by simply inserting the ends under the flat blocks capping the walls.

Then, when you've inevitably produced way more vegetables than you can eat in a season (a common beginner's mistake), you should buy a copy of the USDA's Complete Guide to Home Canning. It's the go-to source on canning, and it's inexpensive. You can get a pressure/canner cooker to accompany canning supplies and Mason jars that run from the high-end All American 930 to the more reasonably-priced Presto 8-Quart cooker.

What's your experience with raised beds and square foot gardening? Help others learn by adding to the comments below. Garden on!

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