Soil Pollution: 4 Things Every Edibles Gardener Needs to Know
#1 Don't Panic.
Soil pollution is a hurdle, but not a full stop barrier. There are things to learn, and examples exist of who is already succeeding using the methods recommended here.
When Lynchburg Grows, a non-profit in central Virginia, decided to start an urban farm on the site of an old warehouse with chemically laden soils (an old industrial rose farm!), everybody thought they were nuts. Until they found out about the raised garden beds. Now Lynchburg Grows provides workforce development and job training opportunities for individuals struggling with disabilities and/or other disadvantages and adds a lot of vegetables to the local food banks.
In Philadelphia, Greensgrow uses hydroponics set ups on their inner-city urban farm plots to grow lettuce on former brownfield (industrial) lots. Now they make a decent living while bringing beauty and fresh foods to the underserved Kensington neighborhood.
If you are going to garden food and have an inkling that your soil might be dubious, here’s what you need to consider:
-know your local history, especially uphill and upstream,
-understand why certain crops are categorically more problematic, and
-learn your options. This is not a full stop, but it might be a delay.
#2 Do Know Your Local History?
Especially uphill and upstream?
Every urban gardener needs to assume they have lead in their soil, and they can test their soil to lead how much. But major industrial operations have gone on in small towns across the country. While everything out there can be tested for, you can’t test for everything. When you send in your soil sample you’ll need to be able to ask “I think there used to be a shoe factory upstream from me. What are the pollutants we should test for?”
#3 Which Crops Are the Safest to Grow in Marginal Soils?
Plants “uptake” soil pollution through their roots. If the contamination is shallow, then deep rooted corn would have a hard time even being exposed, but shallow rooted lettuce will be exposed non-stop. While I’ve seen few studies of soil pollution uptake by root vegetable crops, logic tells us that they’re soaking in it.
Plants generally store pollution in their leaves, another big strike against lettuce, but rarely pass it through to their fruits, another bonus for corn. Also, pollution has to travel through the plant to the storage site. Lettuce? That’s, what, 4 inches? But tomato vine? Could be 6 or 8 feet!
So here’s the rule of thumb: fruits are usually okay, but roots and leafy crops are not a good idea without some intervention. Which leads us naturally to...
#4 What Can Be Done?
Lynchburg Grows and Greensgrow have the gist of it: container gardens or hydroponics. There is another option known as soil remediation. It’s fascinating and complex and I’ll come back to it in a minute.
A raised bed garden is basically a giant container garden. You are building a large pot and then adding fresh soil to it. Mimic nature: add sandier soils at the bottom and soils with higher compost levels at the top. Do not let there be hard defined layers to the soil or the soils won’t share water with each other.
Hydroponics is a whole ‘nother animal. I’m in it for the dirt, but there is a lot of good information out there on how to set up home-scale hydroponics if you want it, but it'll never be pretty.
Soil Remediation is a catch all term for growing something or adding something to the soil to remove the remediation or to temporarily de-activate it. The particulars all depend on the pollution you are trying to pull out: how much and what exactly?
Adding something: if the scientists are telling you to add something to the soil, it’s a fair chance they are telling you to tip your soil pH to be more alkaline. I recommend planting one of the color changing hydrangeas (Hydrangea macrophylla) . They change color along pH lines, so if your hydrangeas start changing color (probably shifting from pink flowers to blue ones), then you’ll know it’s time to do that thing again.
Growing something: This could be phytoremediation (growing plants) or mycoremediation (growing mushrooms or other fungi). It could take 3 years or it could take 100, and what’s going on over that stretch of time varies. One option involves the soil pollution being drawn out of the soil into the plants, in which case you have to yank out the plant periodically, put them in the trash not the compost and grow fresh ones.
Another option is that those plants create good habitat for the particular soil critters who can stabilize or transform the soil pollution. In this case, you can leave those plants to grow, add a few wildflowers, and have yourself an oddly (if invisibly) productive meadow edge.
