The last few years have been a perfect storm for the resurgence of home vegetable (and fruit) gardens. Grapevines are trellised along sidewalks, herbs replace the grass in parking strips, and tiny gardens of carrots and lettuce are shoehorned into any available spot. It’s all good – but we need to be particularly careful about what those plant roots might be taking up along with nutrients and water.
1) Contaminated soil. Many urban (and suburban, and even rural) soils are contaminated with heavy metals, pesticides, and/or industrial wastes. Lead is commonly found in soils near roads (from the old leaded gasoline we used to use) or from old lead-based paint chipping away from houses. Arsenic is a very real problem in North Tacoma soils, for instance, thanks to the smelter that operated there for decades. Overuse and incorrect use of home pesticides will leave residues in the soil for years.
2) Contaminated compost and soil mixes. Many of the same contaminants mentioned above can be found in unregulated composts and soil mixes. (More on this topic here.)
3) Treated lumber. The old treated lumber (CCA = copper, chromium and arsenic) is no longer being sold, but it’s out there. These timbers should not be used around vegetable gardens, as they will leach their heavy metals into the soil. Vegetables vary in their ability to take up and store these metals. (More on this topic here.) Likewise, rubber mulches may leach unwanted chemicals into the soil and should not be used around food plants. (More on this topic here.)
What can you do to avoid these problems? A few things are quick, easy and cheap:
1) Have your soils tested. I’ve mentioned this in an earlier blog on urban soils. It’s the best way to find out exactly what you have in your gardens – the good and the bad.
2) Use only certified composts and soil mixes.
3) Plant in containers if your soils aren’t safe for food. This is especially easy to do with perennial herbs, which can be kept like any other container plant on your deck or porch for years.
4) You can also replace the soil in your vegetable garden. This isn’t quick, easy, or cheap, but is a solution for some people.
I was helping the community garden in my town with a likely lead arsenate problem. The land had formerly been an orchard, and all that pesticide residue is still hanging around. All I can say is, ugh, it's a real mess. I worry that new home gardeners are not getting their soil tested.
Exactly, Shira! When people don't know the history of how garden soil has been treated, there can be serious consequences. I know that in North Tacoma several of my parents' friends (who lived there while the arsenic-spewing smelter was in operation) died from a variety of rare cancers. Exposure to these chemicals is something we can control in our homegrown produce – and I hope people do.
Wow, this is certainly going to scare a lot of urban gardeners into a soil test. Maybe you can give some tips on where to get a soil test done and how to collect a sample? I'd be interested!
I'm going to go tweet this now. Good article.
After the flooding here in NOLA, I had a lot of volunteer Thai basil come up in and around my yard (we had almost 4 feet of water here, and about 4 blocks away was a car repair shop and an embalming facility where the water was between 6-8 feet). The plants stank! I let them get to maturity and before seeding I'd pull them up and put them in the trash. When I first returned, my first attempt at working on my plants – really pulling them up to throw them away – sent me to the doctor's for an antibiotic shot as my throat was swelling shut, and a course of antibiotics. I've no allergies nor am I sickly, but something was in that soil. Now, four years later I still have volunteer basil plants but no more stink. I do think I'll do that test though. Found you from GardenRant – like your site.
Thanks for the kind words, Genevieve and Naomi! I actually have a link on my earlier blog on soils to the University of Massachusetts at Amherst Soil Testing Lab. It's an easily used website with clear instructions and reasonable prices. I can't do a hot link in the comments box, but the address is http://www.umass.edu/plsoils/soiltest/. I don't like scaring people, but after seeing the results of some people's soil test I think this is a serious food safety issue. And Naomi, the issue with flooding and contaminating soil hadn't even occurred to me. Thank you for telling your story.
I have had one soil test (a composite from eight locations around a 50×100 lot) by the University of Maine, and the soil report informed me that lead levels were so high that if soil were removed and trucked off-site, a hazardous waste permit would be required. Later I found that our 80-year-old house had been built on a former tannery site, and between that and leaded gasoline and paint, I may never veg garden.
Interestingly, there have been some projects in the city to see whether certain crops will take up the lead and remove it, decontaminating the soil. I tried contacting the researchers but never got a response.
The thing with lead is it doesn't go away — those crops can't be composted or burned, because it just recycles the lead — so I really wanted to know what was being done with the crops after the fact.
What a terrifying story! I'll do some digging around to see if there are some lead-eating plants that have been identified. I do know that a particular fern will take up arsenic, and many wetland trees and shrubs will take up heavy metals (and ideally they are taken to a hazardous waste site before they die and release all those metals back into the soil). Thanks for post!
Thanks for this great post. Heavy metals and other contaminants in garden soils seem to get attention every few years, but with so many people taking up veg. gardening now it seems even more important to urge soil testing.