Concrete blocks for garden beds

[David Hare-Scott]

I am planning to build raised vegetable garden beds. One option is to use manufactured hollow concrete blocks. The beds will be 1.4 m (4 ft) by 10 m (30 ft). the standard blocks are nominally 200mm (8 ") high so I need two courses high. This will be built on a site that has a gentle slope, the area for the beds will be levelled beforehand. Drains will be built to prevent ground water from coursing through the vege garden. We don't have earthquakes, snow, floods, tornados or hurricanes.

The soil is dark and fertile but rather heavy with quite a high proportion of clay. The inside of the beds will be filled with this soil amended with compost etc. The blocks come in nominal 100mm (4")

150mm (6") and 200mm (8") widths. The price of the blocks is roughly proportionate to the width.

My question is what kind of construction do I need to make these beds stable while not spending time and money over-engineering them? I don't mind the odd small crack here or there but the walls must not fall over.

As I see it the walls would be stretcher bond but could be:

1) laid dry 2) mortared 3) reinforced 4) mortared and reinforced

Obviously the cheapest will be 100mm blocks laid dry but I wonder if they will be stable. Mortared and reinforced 200mm will be very strong but also rather expensive. What is by best compromise that is stable under these conditions for the least cost?

David

[Tsu Dho Nimh]

Lay up the courses and pound 3/8" rebar "hairpins" or "candy canes" through the holes into the dirt every couple of feet. Pass the ends of the rebar over the intersection of two blocks, through the holes and into the dirt.

This will make it stable enough to keep the vegetables from escaping, but if you want to enlarge or remove, you just yank out the rebar and unstack the blocks.

Tsu

-- To doubt everything or to believe everything are two equally convenient solutions; both dispense with the necessity of reflection.

- Jules Henri Poincaré

[V_coerulea]

[Rick Samuel]

Dry stack, pound in 5/8 rebar down flush or lower then top, fill all holes w/ dirt. To make more stable, mix in 10% cement / the dirt. But just soil is good for two courses.

[Steve Coyle]

Howdy folks, On the production side of the garden bed, run some weed cloth down the inside of the block to prevent some of your weeds like Bermuda grass that propagate underground from taking up residence under the blocks or in the cavities or else you'll be fighting them forever. On the outside of the walls holding a garden bed, run some weed cloth flat, and cover with a heavy mulch to keep the weeds away from the wall, and save on trimmer string. This is more of a gardening tip than a construction tip but you do want to do it when you build the wall so it is a consideration during construction.

Steve Coyle

[AF]

[vincent p. norris]

I made a raised bed at least five years ago with two courses of blocks. I merely leveled the ground they would rest on, as well as I could.

I used no mortar, rebar, or anything else.

I've had no trouble with them.

vince norris