I have been planning and spearheading a school garden at my children's elementary school in Golden Co for the last year and a half. As a Learning Garden committee we decided that using concrete blocks as a raised bed material would be more sustainable than using any treated wood which would possibly expose our soil to chemicals.
We received an amazing grant from our local Lowe's and they are building our raised beds for us. After the first weekend of work a teacher came into school and saw that the raised beds were made of cinder blocks and said that they are potentially dangerous as well!! Oy!! We had never heard of this and after some internet research and speaking with an expert we have learned the problem is when these bricks are made with Fly Ash (which ours are - an 8% concentration) which is a by-product of coal - they can leach things such as radium and arsenic. Seems like this may not happen unless the bricks are actually fractured but since the potential is there and we have caught it early we want to do something about it.
Does anyone out there know anything about this? The solutions seem to be sealing the bricks - which would be using some sort of chemical product which we would prefer to avoid. Or lining the sides of the beds with a heavy plastic to avoid the soil contacting the bricks.
I would love any insight or tips that anyone has.....I'm sort of freaking out as we hope to fill our beds with soil this weekend.
Many many thanks in advance!
Liz Bravman
Glad to hear that you are introducing gardening to your child's school! So much can be learned through gardening.
In the research that I did for your question the main thing that I found was that the blocks will (over time) leach lime which alters the soil's pH. Because of the fly ash there is the possibility of some leaching of other compounds, however I did not find any conclusive research that deemed them dangerous to use for your application. There is a lot of anecdotal information online from various sources, but again, I didn't find any science based research. In fact most of the Extension sources I found from universities around the country still recommend using them for raised bed gardens. There are studies that show that using treated wood is not okay.
Since I'm not able to provide conclusive evidence, if you feel more comfortable, you can always line the blocks with a thick (6 mil) plastic. Don't line the bottom however, because you want the soil to be able to drain rather than create a pond. Or, you can use another material like untreated wood planks.
Good luck. I hope your garden is a success!
Many thanks Deryn! Your expertise combined with knowledge from our local extension and local health department has made our committee feel at ease. Its frightening what unscientific information you can come across on the internet! Unfortunately we could not find any BPA-free plastic so we opted to put in no liner and will ask students to plant 12" (the recommendation for treated wood) from the sides of the bed.
Thank you again for your assistance!
Best,
Liz
Sounds like a good plan. Hope you have a great garden!
FAQs
Cinder blocks haven't been mass produced with fly ash in the U.S. for 50 years, though. The cinder blocks that you buy in the store today are actually concrete blocks and totally safe. Unless you're using antique cinder blocks, there should be no reason to worry, especially when cinder block gardening for vegetables.
Can you use cinder blocks for a garden? ›
The quick-and-dirty way of building a raised cinder block garden is to arrange the blocks, fill in the perimeter with dirt, and start planting. But there's a little more to it if you want it to thrive and look beautiful, too. Here, we'll walk you through how to create a four-by-eight-foot cinder block garden bed.
Can I use concrete blocks for raised beds? ›
This raised bed is made from concrete blocks and topped off with timber sleepers to provide extra seating space, invaluable in a small garden. With basic DIY skills, plus a couple of spare weekends, you'll soon have a 2.2m x 1.4m raised bed that will provide space for ornamental and edible plants for years to come.
What is the safest material for raised garden beds? ›
Build your raised bed with a decay-resistant type of wood, such as cedar, black cherry, oak (bur, chestnut, post, white), black locust, Osage orange, or redwood. (Source: USDA Forest Products Lab) Use a non-wood material such as stones, concrete blocks, bricks, or synthetic lumber.
Does concrete leach chemicals into soil? ›
The bottom line is that the cement in your soil or planter can be deadly for your cherished plants. So, it's better to take preventive steps than to find a cure after the damage has been done. Because the harmful properties present in cement will definitely destroy your plants' survival rate.
How long do cinder block garden beds last? ›
Although it costs more to create these concrete raised beds, they are pretty permanent. We plan to use ours for over 20 years, so our pro-rated cost per bed over time (for both soil and blocks) is under $18 per year.
What are the cons of cinder block? ›
Five Concrete Block Home Disadvantages
- Concrete blocks are less expensive than bricks. ...
- Concrete block homes can lack curb appeal. ...
- This material may not be suitable for specific regional preferences. ...
- Some blocks may need to be removed to reach the utilities or make any changes.
20 blocks will give an interior bed area of 4′ x 8′. Leave a side open to bring in the soil until the new bed is filled. No mortar or special installation is necessary unless you desire a bed which is higher than 8″ raised over the surrounding area.
What is the difference between cinder block and cement block? ›
Cinder block is made of- concrete and coal cinders. Concrete block is produced from steel, wood, and cement. Cinder blocks are lighter than concrete blocks.
What do I put on the bottom of a raised garden bed on concrete? ›
When setting up a raised garden bed on concrete, drainage and root health are key concerns. Start with a layer of landscape fabric to prevent soil from washing out. Above this, a layer of gravel or small stones can aid in drainage. Then, fill the bed with a mix of topsoil, compost, and other organic matter.
Safe for All
ProWood MCA-treated wood products may be used in or around plants and produce gardens. Copper is a safe biocide used internationally to protect crops from disease.
Do cinder blocks leach chemicals? ›
Most studies have found that the chemicals do not leach from concrete, they are tied up in the cement matrix. This includes fly ash (which has mercury and other heavy metals). Concrete, even with fly ash or blast furnace slag, has been deemed safe enough to use in the pipes for drinking water.
Are cinder blocks safe for vegetable gardens? ›
Stay away from old-fashioned cinder blocks, which may contain heavy metals—not a good thing for food gardens. Second, a concrete block bed can affect your soil's pH, making it more alkaline, so it's not good for growing acid-loving plants like blueberries.
How to build a non-toxic raised garden bed? ›
You don't have to build the frame out of wood for your raised bed garden to be truly organic. Other options are bricks, flagstone, or even large river rocks. (Add a non-toxic garden bed liner to hold the soil in place.) Steer clear of concrete; it may leach into your soil and alter soil acidity.
Did cinder blocks contain asbestos? ›
Yes, asbestos was used in cement formulations of all kinds from the 1930s to the 1980s. Cinder blocks manufactured during this time period were no exception.
Is cinder block dust toxic? ›
Concrete dust can be very harmful. Even the slightest amount of exposure can cause irritation to the eyes, nose, and throat. Prolonged exposure can lead to lung cancer and other respiratory problems.
Are cinder blocks toxic in water? ›
Basic concrete blocks aren't manufactured with any ingredients or materials that are particularly hazardous to the water or fish. If anything was added to the outside of the block while it was used for another purpose, something hazardous could leach out.
