Using Concrete Blocks for a raised bed - unsafe?

Hi,

On our community allotment plot we have inherited some old concrete blocks - it's been suggested to use them for a raised bed but one person in our group is concerned that they can leach dangerous chemicals into the soil. Others seem to think it's nothing to worry about.

Can anyone confirm if they are safe for food growing or not? There seems to be conflicting advice on various internet sites, and most of the info I can find is American, so I'm not sure if what they call 'cinder blocks' are made up in the same way as UK concrete blocks.

Thanks,

Andy

 

As far back as I can remember they always used power station waste ash in them

Pulverised fuel ash - Wikipedia

And if you're thinking it'll change after UK coal fire power stations are phased out Where Have all the Blocks Gone? | Homebuilding & Renovating

 

I would err on the side of caution and not use concrete blocks for edible crops.

Chemical additives are some times used in the concrete mix to alter its working characteristics and it is these that I am most concerned about.

 

@AndyS If well weathered then most things will have leached out of them. Also if used in raised beds anything leaching out will tend to move down more than sideways and leaving a 6" gap will alleviate most problems. You could also line the inner side of the raised beds with split compost bags which would prevent contact with the blocks.

 

Oh god, and I've got a concrete path
And it is in contact with the soil.

I'm still alive, well almost.

 

Others might have concrete blockwork used in their house/garage foundations, but if so, I don't think it's a good idea to dig deep trenches down to the bottom of the concrete footings all around your property and line your foundations with old plastic compost bags.

 

I'd have thought that the only problems that might arise are if you want to grow ericaceous-loving plants in them...e.g. blackcurrants, blueberries. Shouldn't be a problem with brassicas as they prefer a bit of lime in the soil. If the blocks have old mortar residues, they could alter the ph of the soil a bit, but as NigelJ says, lining the inside of the beds with plastic sacks would stop leaching. What the plastic leaches into the soil is another story If you do go down that route, keep an eye open for colonies of snails...they love hollow spaces to lurk in!

 

Googling will find as many reports of plastic toxins as it will find reports about concrete blockwork toxins

Plastic flower pots, seeds trays, compost bags, etc. are all supposed to leach toxins and contaminate your soil/plants as none of them are food safe. Non foodsafe hosepipes should not be used according to some reports. Follow their advice and you'd only grow stuff in plastic coffee cups and margarine/icecream tubs.

And as Sunflowers are supposed to take contaminants from the soil, when growing in suspect ground should they have their flowers removed to prevent poisoning of bees and birds, then be binned rather than composted?