By Connie Oswald Stofko
Is it safe to use cinder blocks in a raised bed, or might chemicals from the concrete blocks leach out of the blocks to contaminate your soil and food plants you grow there?
Can you use pressure treated lumber?
Can you grow food plants in the hellstrip, the area between the street and sidewalk?
John Farfaglia, extension educator with Cornell Cooperative Extension in Niagara County, responded to my questions on soil safety.
Cinder blocks in raised vegetable bed
I have seen warnings on the Internet that cinder blocks or concrete blocks used in a garden might leach harmful chemicals into the soil and ultimately into your food plants.
After doing some research, Farfaglia’s short answer was: “I doubt whether there is any issue to worry about.”
He found universities recommending the use of concrete blocks in container gardens or raised beds.
The concern cited in many warnings is specifically fly ash, the residue you get from burning coal, that might have been used in older cinder blocks, but he doubts whether that is commonly used anymore.
However, one thing you should take into consideration when using old bricks, old concrete blocks or other recycled material is where those materials came from, he said. The materials may have been resting in soil that was contaminated with chemicals. If you’re going to use bricks for pathways, pressure washing the materials should be sufficient. If you’re using materials for a vegetable garden, you would want to be more cautious.
If you’re unsure of the source of used materials, he recommends using new material.
Pressure treated lumber in raised vegetable bed
Farfaglia said people often ask about using treated lumber for raised beds. At one time, arsenic was used in treated lumber, but isn’t any longer, he said. The risk of using new treated lumber is low, but he still recommends using natural wood such as cedar to be safe.
Line a raised bed to protect against potential leaching
As added protection, when growing food in a raised bed, you can line the bed with plastic to act as a barrier from any chemicals that might leach into the soil from the building materials. Use a thick gauge plastic, like 6 mil, Farfaglia said.
Hellstrip not best option for food plants
I asked Farfaglia about it, and he cautions against it.
“In a lot of cases the risk is not high, but as a general practice, save that strip for ornamental plants, ” he said.
That area can contain residues from salt and other chemicals used on the road, and there may be a higher concentration of lead still there from auto exhaust.
You should also be wary of beds near the foundation of an older home that may be contaminated with lead from paint that flaked off and accumulated in the soil, he noted.
If your soil is contaminated, rinsing your herbs or vegetables might not be enough to get rid of the contamination. How big the risk is depends on many factors, including how high the concentration of the contaminant is, how often you eat the food and how you cook it.
