We’re building raised flower beds and fitting to the industrial raw look of our house we want to use concrete blocks.
Concrete blocks are flexible to use, inviting to play Giant Lego, so we might even turn some of the top row on the side, functioniong as additional planters.
Our garden is square, surrounded by boundary walls. The idea is for the flower beds to run along two of the walls, in an L-shape.
All we need to do for that is build a parallel smaller wall next to the two higher boundary walls. Doing a proper job, we need a concrete foundation for this wall.
So we have concrete blocks and a fresh concrete foundation holding up the raised flower beds in which we want to grow our vegetables. The question is:
Is concrete bad for your garden?
Concrete is the mixture of sand, gravel, cement and water.
Premanufactured concrete such as concrete blocks can contain fly ash, which is toxic.
Cement contains a variety of materials, such as limestone, shells, chalk, shale, clay, slate, blast furnace slag, silica sand, iron ore, some of which are harmful.
Even when the cement is dry, lime leaches into the soil which raises its pH levels. Plants usually like a slightly acidic to neutral soil, in the 6.0 to 7.0 pH range.
Protect soil from the effects of adjacent concrete
If you’re concerned unwanted substances might be leaching from concrete into soil, you can protect your soil:
– Seal concrete blocks with concrete sealant and polymer paint.
– Line the concrete blocks with plastic sheeting.
If you just want to deal with the altered pH level, you can treat your soil:
– Use sulphur to lower the soil’s pH level.
– Any acidic substance can help reduce the pH level, as long as it’s not too much acid for the plants. Funny enough, dog wee could be beneficial.
– As a quick fix, water affected plants with a white vinegar solution.
– Plant greens that prefer a more alkaline soil, for example Clematis, Asparagus, Ferns.